Misplaced Pages

#934065

130-470: An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode , an electrode of the device through which conventional current leaves the device. A common mnemonic is ACID, for "anode current into device". The direction of conventional current (the flow of positive charges) in a circuit is opposite to the direction of electron flow, so (negatively charged) electrons flow from

260-420: A cathode and a plate . The cathode is either indirectly heated or directly heated . If indirect heating is employed, a heater is included in the envelope. In operation, the cathode is heated to red heat , around 800–1,000 °C (1,470–1,830 °F). A directly heated cathode is made of tungsten wire and is heated by a current passed through it from an external voltage source. An indirectly heated cathode

390-400: A rechargeable battery when it is being charged, the roles of the electrodes as anode and cathode are reversed. Conventional current depends not only on the direction the charge carriers move, but also the carriers' electric charge . The currents outside the device are usually carried by electrons in a metal conductor. Since electrons have a negative charge, the direction of electron flow

520-499: A circuit is given by its current–voltage characteristic . The shape of the curve is determined by the transport of charge carriers through the so-called depletion layer or depletion region that exists at the p–n junction between differing semiconductors. When a p–n junction is first created, conduction-band (mobile) electrons from the N- doped region diffuse into the P- doped region where there

650-486: A current can be applied to the working electrode . The counter electrode is usually made of an inert material, such as a noble metal or graphite , to keep it from dissolving. In arc welding , an electrode is used to conduct current through a workpiece to fuse two pieces together. Depending upon the process, the electrode is either consumable, in the case of gas metal arc welding or shielded metal arc welding , or non-consumable, such as in gas tungsten arc welding . For

780-422: A current of electrons flows through the tube from cathode to plate. When the plate voltage is negative with respect to the cathode, no electrons are emitted by the plate, so no current can pass from the plate to the cathode. Point-contact diodes were developed starting in the 1930s, out of the early crystal detector technology, and are now generally used in the 3 to 30 gigahertz range. Point-contact diodes use

910-404: A definite " knee " around this threshold when viewed on a linear scale, the knee is an illusion that depends on the scale of y-axis representing current. In a semi-log plot (using a logarithmic scale for current and a linear scale for voltage), the diode's exponential curve instead appears more like a straight line. Since a diode's forward-voltage drop varies only a little with the current, and

1040-449: A direct current system, the weld rod or stick may be a cathode for a filling type weld or an anode for other welding processes. For an alternating current arc welder, the welding electrode would not be considered an anode or cathode. For electrical systems which use alternating current , the electrodes are the connections from the circuitry to the object to be acted upon by the electric current but are not designated anode or cathode because

1170-491: A direction "from East to West, or, which will strengthen this help to the memory, that in which the sun appears to move", the anode is where the current enters the electrolyte, on the East side: " ano upwards, odos a way; the way which the sun rises". The use of 'East' to mean the 'in' direction (actually 'in' → 'East' → 'sunrise' → 'up') may appear contrived. Previously, as related in the first reference cited above, Faraday had used

1300-404: A given selection of constituents of the electrode, the final efficiency is determined by the internal structure of the electrode. The important factors in the internal structure in determining the performance of the electrode are: These properties can be influenced in the production of the electrodes in a number of manners. The most important step in the manufacturing of the electrodes is creating

1430-399: A heated cathode and a plate , in which electrons can flow in only one direction, from the cathode to the plate. Among many uses, diodes are found in rectifiers to convert alternating current (AC) power to direct current (DC), demodulation in radio receivers , and can even be used for logic or as temperature sensors . A common variant of a diode is a light-emitting diode , which

SECTION 10

#1732863126935

1560-401: A high volumetric one. Furthermore, Silicon has the advantage of operating under a reasonable open circuit voltage without parasitic lithium reactions. However, silicon anodes have a major issue of volumetric expansion during lithiation of around 360%. This expansion may pulverize the anode, resulting in poor performance. To fix this problem, scientists looked into varying the dimensionality of

1690-733: A highly efficient conductive network that securely binds lithium iron phosphate particles, adding carbon nanotubes as a conductive additive at a dosage of just 0.5 wt.% helps cathodes to achieve a remarkable rate capacity of 161.5 mAh g-1 at 0.5 C and 130.2 mAh g-1 at 5 C, whole maintaining 87.4% capacity retention after 200 cycles at 2 C. The anodes used in mass-produced Li-ion batteries are either carbon based (usually graphite) or made out of spinel lithium titanate (Li 4 Ti 5 O 12 ). Graphite anodes have been successfully implemented in many modern commercially available batteries due to its cheap price, longevity and high energy density. However, it presents issues of dendrite growth, with risks of shorting

1820-411: A low work function , meaning that they more readily emit electrons than would the uncoated cathode. The plate, not being heated, does not emit electrons; but is able to absorb them. The alternating voltage to be rectified is applied between the cathode and the plate. When the plate voltage is positive with respect to the cathode, the plate electrostatically attracts the electrons from the cathode, so

1950-572: A lower cost, however there are some problems associated with using manganese. The main problem is that manganese tends to dissolve into the electrolyte over time. For this reason, cobalt is still the most common element which is used in the lithium compounds. There is much research being done into finding new materials which can be used to create cheaper and longer lasting Li-ion batteries For example, Chinese and American researchers have demonstrated that ultralong single wall carbon nanotubes significantly enhance lithium iron phosphate cathodes. By creating

2080-419: A more electrically reactive (less noble) metal attached to the vessel hull and electrically connected to form a cathodic protection circuit. A less obvious example of this type of protection is the process of galvanising iron. This process coats iron structures (such as fencing) with a coating of zinc metal. As long as the zinc remains intact, the iron is protected from the effects of corrosion. Inevitably,

2210-399: A more extensive mathematical treatment one could read the paper by Newton. An interpretation of this result and what a closer look at the physical meaning of the λ {\displaystyle \lambda } one can read the paper by Marcus. the situation at hand can be more accurately described by using the displaced harmonic oscillator model, in this model quantum tunneling

2340-415: A particular type of diode in a circuit diagram conveys the general electrical function to the reader. There are alternative symbols for some types of diodes, though the differences are minor. The triangle in the symbols points to the forward direction, i.e. in the direction of conventional current flow. There are a number of common, standard and manufacturer-driven numbering and coding schemes for diodes;

2470-492: A positively charged electroscope, but not a negatively charged electroscope. In 1880, Thomas Edison observed unidirectional current between heated and unheated elements in a bulb, later called Edison effect , and was granted a patent on application of the phenomenon for use in a DC voltmeter . About 20 years later, John Ambrose Fleming (scientific adviser to the Marconi Company and former Edison employee) realized that

2600-452: A process called rectification . As rectifiers, diodes can be used for such tasks as extracting modulation from radio signals in radio receivers . A diode's behavior is often simplified as having a forward threshold voltage or turn-on voltage or cut-in voltage , above which there is significant current and below which there is almost no current, which depends on a diode's composition: This voltage may loosely be referred to simply as

2730-490: A radio carrier wave, whose amplitude or envelope is proportional to the original audio signal. The diode rectifies the AM radio frequency signal, leaving only the positive peaks of the carrier wave. The audio is then extracted from the rectified carrier wave using a simple filter and fed into an audio amplifier or transducer , which generates sound waves via audio speaker . In microwave and millimeter wave technology, beginning in

SECTION 20

#1732863126935

2860-438: A region on one side that contains negative charge carriers (electrons), called an n-type semiconductor , and a region on the other side that contains positive charge carriers ( holes ), called a p-type semiconductor . When the n-type and p-type materials are attached together, a momentary flow of electrons occurs from the n to the p side resulting in a third region between the two where no charge carriers are present. This region

2990-409: A result of the oxidation reaction. In an electrolytic cell , the anode is the wire or plate upon which excess positive charge is imposed. As a result of this, anions will tend to move towards the anode where they will undergo oxidation. Historically, the anode of a galvanic cell was also known as the zincode because it was usually composed of zinc. The terms anode and cathode are not defined by

3120-467: A small diameter metal wire in contact with a semiconductor crystal, and are of either non-welded contact type or welded contact type. Non-welded contact construction utilizes the Schottky barrier principle. The metal side is the pointed end of a small diameter wire that is in contact with the semiconductor crystal. In the welded contact type, a small P region is formed in the otherwise N-type crystal around

3250-422: A specific task. Typical constituents are the active materials which serve as the particles which oxidate or reduct, conductive agents which improve the conductivity of the electrode and binders which are used to contain the active particles within the electrode. The efficiency of electrochemical cells is judged by a number of properties, important quantities are the self-discharge time, the discharge voltage and

3380-401: A variety of other minerals as detectors. Semiconductor principles were unknown to the developers of these early rectifiers. During the 1930s understanding of physics advanced and in the mid-1930s researchers at Bell Telephone Laboratories recognized the potential of the crystal detector for application in microwave technology. Researchers at Bell Labs , Western Electric , MIT , Purdue and in

3510-414: A zinc anode and a manganese oxide cathode in which ZnO is formed. The half-reactions are: Overall reaction: The ZnO is prone to clumping and will give less efficient discharge if recharged again. It is possible to recharge these batteries but is due to safety concerns advised against by the manufacturer. Other primary cells include zinc–carbon , zinc–chloride , and lithium iron disulfide. Contrary to

3640-469: Is manganese . The best choice of compound usually depends on the application of the battery. Advantages for cobalt-based compounds over manganese-based compounds are their high specific heat capacity, high volumetric heat capacity , low self-discharge rate, high discharge voltage and high cycle durability. There are however also drawbacks in using cobalt-based compounds such as their high cost and their low thermostability . Manganese has similar advantages and

3770-403: Is a "built-in" potential across the depletion zone. If an external voltage is placed across the diode with the same polarity as the built-in potential, the depletion zone continues to act as an insulator, preventing any significant electric current flow (unless electron–hole pairs are actively being created in the junction by, for instance, light; see photodiode ). However, if the polarity of

3900-427: Is a large population of holes (vacant places for electrons) with which the electrons "recombine". When a mobile electron recombines with a hole, both hole and electron vanish, leaving behind an immobile positively charged donor (dopant) on the N side and negatively charged acceptor (dopant) on the P side. The region around the p–n junction becomes depleted of charge carriers and thus behaves as an insulator . However,

4030-417: Is a theory originally developed by Nobel laureate Rudolph A. Marcus and explains the rate at which an electron can move from one chemical species to another, for this article this can be seen as 'jumping' from the electrode to a species in the solvent or vice versa. We can represent the problem as calculating the transfer rate for the transfer of an electron from donor to an acceptor The potential energy of

Anode - Misplaced Pages Continue

4160-491: Is a two- terminal electronic component that conducts current primarily in one direction (asymmetric conductance ). It has low (ideally zero) resistance in one direction and high (ideally infinite) resistance in the other. A semiconductor diode, the most commonly used type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. It has an exponential current–voltage characteristic . Semiconductor diodes were

4290-414: Is allowed. This is needed in order to explain why even at near-zero Kelvin there still are electron transfers, in contradiction to the classical theory. Without going into too much detail on how the derivation is done, it rests on using Fermi's golden rule from time-dependent perturbation theory with the full Hamiltonian of the system. It is possible to look at the overlap in the wavefunctions of both

4420-493: Is always based on the forward current direction. Electrode Michael Faraday coined the term " electrode " in 1833; the word recalls the Greek ἤλεκτρον ( ḗlektron , "amber") and ὁδός ( hodós , "path, way"). The electrophore , invented by Johan Wilcke in 1762, was an early version of an electrode used to study static electricity . Electrodes are an essential part of any battery . The first electrochemical battery

4550-473: Is approximately proportional to the square of the input voltage, so the response is called square law in this region. Following the end of forwarding conduction in a p–n type diode, a reverse current can flow for a short time. The device does not attain its blocking capability until the mobile charge in the junction is depleted. The effect can be significant when switching large currents very quickly. A certain amount of "reverse recovery time" t r (on

4680-401: Is being done into increasing the efficiency, safety and reducing the costs of these electrodes specifically. In Li-ion batteries, the cathode consists of a intercalated lithium compound (a layered material consisting of layers of molecules composed of lithium and other elements). A common element which makes up part of the molecules in the compound is cobalt . Another frequently used element

4810-447: Is called the depletion region because there are no charge carriers (neither electrons nor holes) in it. The diode's terminals are attached to the n-type and p-type regions. The boundary between these two regions, called a p–n junction , is where the action of the diode takes place. When a sufficiently higher electrical potential is applied to the P side (the anode ) than to the N side (the cathode ), it allows electrons to flow through

4940-413: Is electrically linked to the protected system. As a result, the metal anode partially corrodes or dissolves instead of the metal system. As an example, an iron or steel ship's hull may be protected by a zinc sacrificial anode , which will dissolve into the seawater and prevent the hull from being corroded. Sacrificial anodes are particularly needed for systems where a static charge is generated by

5070-403: Is heated by infrared radiation from a nearby heater that is formed of Nichrome wire and supplied with current provided by an external voltage source. The operating temperature of the cathode causes it to release electrons into the vacuum, a process called thermionic emission . The cathode is coated with oxides of alkaline earth metals , such as barium and strontium oxides . These have

5200-499: Is in lithium-ion batteries (Li-ion batteries). A Li-ion battery is a kind of flow battery which can be seen in the image on the right. Furthermore, a Li-ion battery is an example of a secondary cell since it is rechargeable. It can both act as a galvanic or electrolytic cell . Li-ion batteries use lithium ions as the solute in the electrolyte which are dissolved in an organic solvent . Lithium electrodes were first studied by Gilbert N. Lewis and Frederick G. Keyes in 1913. In

5330-494: Is mechanical shock, which breaks either the electrode or the system's container, leading to poor conductivity and electrolyte leakage. However, the relevance of mechanical properties of electrodes goes beyond the resistance to collisions due to its environment. During standard operation, the incorporation of ions into electrodes leads to a change in volume. This is well exemplified by Si electrodes in lithium-ion batteries expanding around 300% during lithiation. Such change may lead to

Anode - Misplaced Pages Continue

5460-545: Is more so a function of temperature, this effect can be used as a temperature sensor or as a somewhat imprecise voltage reference . A diode's high resistance to current flowing in the reverse direction suddenly drops to a low resistance when the reverse voltage across the diode reaches a value called the breakdown voltage . This effect is used to regulate voltage ( Zener diodes ) or to protect circuits from high voltage surges ( avalanche diodes ). A semiconductor diode's current–voltage characteristic can be tailored by selecting

5590-399: Is now the pre-exponential factor has now been described by more physical parameters instead of the experimental factor A {\displaystyle A} . One is once again revered to the sources as listed below for a more in-depth and rigorous mathematical derivation and interpretation. The physical properties of electrodes are mainly determined by the material of the electrode and

5720-557: Is obtained very similar to the classically derived formula, as expected. w E T = | J | 2 ℏ π λ k T exp ⁡ [ − ( Δ E + λ ) 2 4 λ k T ] {\displaystyle w_{ET}={\frac {|J|^{2}}{\hbar }}{\sqrt {\frac {\pi }{\lambda kT}}}\exp \left[{\frac {-(\Delta E+\lambda )^{2}}{4\lambda kT}}\right]} The main difference

5850-455: Is opposite to the direction of conventional current. Consequently, electrons leave the device through the anode and enter the device through the cathode. The definition of anode and cathode is different for electrical devices such as diodes and vacuum tubes where the electrode naming is fixed and does not depend on the actual charge flow (current). These devices usually allow substantial current flow in one direction but negligible current in

5980-454: Is the positively charged electron collector. In a tube, the anode is a charged positive plate that collects the electrons emitted by the cathode through electric attraction. It also accelerates the flow of these electrons. [REDACTED] In a semiconductor diode , the anode is the P-doped layer which initially supplies holes to the junction. In the junction region, the holes supplied by

6110-653: Is the reorganisation energy. Filling this result in the classically derived Arrhenius equation k = A exp ⁡ ( − Δ G † k T ) , {\displaystyle k=A\,\exp \left({\frac {-\Delta G^{\dagger }}{kT}}\right),} leads to k = A exp ⁡ [ − ( Δ G 0 + λ ) 2 4 λ k T ] {\displaystyle k=A\,\exp \left[{\frac {-(\Delta G^{0}+\lambda )^{2}}{4\lambda kT}}\right]} With A being

6240-417: Is used as electric lighting and status indicators on electronic devices. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking it in the opposite direction (the reverse direction). Its hydraulic analogy is a check valve . This unidirectional behavior can convert alternating current (AC) to direct current (DC),

6370-409: Is used to coat steel, when a breach of the coating occurs it actually accelerates oxidation of the iron. Another cathodic protection is used on the impressed current anode. It is made from titanium and covered with mixed metal oxide . Unlike the sacrificial anode rod, the impressed current anode does not sacrifice its structure. This technology uses an external current provided by a DC source to create

6500-546: Is useful in microwave and switching circuits. Diodes, both vacuum and semiconductor, can be used as shot-noise generators . Thermionic ( vacuum-tube ) diodes and solid-state (semiconductor) diodes were developed separately, at approximately the same time, in the early 1900s, as radio receiver detectors . Until the 1950s, vacuum diodes were used more frequently in radios because the early point-contact semiconductor diodes were less stable. In addition, most receiving sets had vacuum tubes for amplification that could easily have

6630-464: The Shockley diode equation article. In detector and mixer applications, the current can be estimated by a Taylor's series. The odd terms can be omitted because they produce frequency components that are outside the pass band of the mixer or detector. Even terms beyond the second derivative usually need not be included because they are small compared to the second order term. The desired current component

SECTION 50

#1732863126935

6760-525: The UK intensively developed point-contact diodes ( crystal rectifiers or crystal diodes ) during World War II for application in radar. After World War II, AT&T used these in its microwave towers that criss-crossed the United States, and many radar sets use them even in the 21st century. In 1946, Sylvania began offering the 1N34 crystal diode. During the early 1950s, junction diodes were developed. In 2022,

6890-486: The cycle performance . The physical properties of the electrodes play an important role in determining these quantities. Important properties of the electrodes are: the electrical resistivity , the specific heat capacity (c_p), the electrode potential and the hardness . Of course, for technological applications, the cost of the material is also an important factor. The values of these properties at room temperature (T = 293 K) for some commonly used materials are listed in

7020-651: The diode law (named after the bipolar junction transistor co-inventor William Bradford Shockley ) models the exponential current–voltage (I–V) relationship of diodes in moderate forward or reverse bias. The article Shockley diode equation provides details. At forward voltages less than the saturation voltage, the voltage versus current characteristic curve of most diodes is not a straight line. The current can be approximated by I = I S e V D / ( n V T ) {\displaystyle I=I_{\text{S}}e^{V_{\text{D}}/(nV_{\text{T}})}} as explained in

7150-499: The semiconductor materials and the doping impurities introduced into the materials during manufacture. These techniques are used to create special-purpose diodes that perform many different functions. For example, to electronically tune radio and TV receivers ( varactor diodes ), to generate radio-frequency oscillations ( tunnel diodes , Gunn diodes , IMPATT diodes ), and to produce light ( light-emitting diodes ). Tunnel, Gunn and IMPATT diodes exhibit negative resistance , which

7280-434: The "unilateral conduction" across a contact between a metal and a mineral . Indian scientist Jagadish Chandra Bose was the first to use a crystal for detecting radio waves in 1894. The crystal detector was developed into a practical device for wireless telegraphy by Greenleaf Whittier Pickard , who invented a silicon crystal detector in 1903 and received a patent for it on 20 November 1906. Other experimenters tried

7410-417: The 1930s, researchers improved and miniaturized the crystal detector. Point contact diodes ( crystal diodes ) and Schottky diodes are used in radar, microwave and millimeter wave detectors. Rectifiers are constructed from diodes, where they are used to convert alternating current (AC) electricity into direct current (DC). Automotive alternators are a common example, where the diode, which rectifies

7540-546: The AC into DC, provides better performance than the commutator or earlier, dynamo . Similarly, diodes are also used in Cockcroft–Walton voltage multipliers to convert AC into higher DC voltages. Since most electronic circuits can be damaged when the polarity of their power supply inputs are reversed, a series diode is sometimes used to protect against such situations. This concept is known by multiple naming variations that mean

7670-603: The Edison effect could be used as a radio detector . Fleming patented the first true thermionic diode, the Fleming valve , in Britain on 16 November 1904 (followed by U.S. patent 803,684 in November 1905). Throughout the vacuum tube era, valve diodes were used in almost all electronics such as radios, televisions, sound systems, and instrumentation. They slowly lost market share beginning in

7800-516: The Si. Many studies have been developed in Si nanowires , Si tubes as well as Si sheets. As a result, composite hierarchical Si anodes have become the major technology for future applications in lithium-ion batteries. In the early 2020s, technology is reaching commercial levels with factories being built for mass production of anodes in the United States. Furthermore, metallic lithium is another possible candidate for

7930-433: The action of flowing liquids, such as pipelines and watercraft. Sacrificial anodes are also generally used in tank-type water heaters. In 1824 to reduce the impact of this destructive electrolytic action on ships hulls, their fastenings and underwater equipment, the scientist-engineer Humphry Davy developed the first and still most widely used marine electrolysis protection system. Davy installed sacrificial anodes made from

SECTION 60

#1732863126935

8060-467: The added stress and, therefore changes the battery's performance. Furthermore, mechanical stresses may also impact the electrode's solid-electrolyte-interphase layer. The interface which regulates the ion and charge transfer and can be degraded by stress. Thus, more ions in the solution will be consumed to reform it, diminishing the overall efficiency of the system. In a vacuum tube or a semiconductor having polarity ( diodes , electrolytic capacitors )

8190-444: The anode (even though it is negative and therefore would be expected to attract them, this is due to electrode potential relative to the electrolyte solution being different for the anode and cathode metal/electrolyte systems); but, external to the cell in the circuit, electrons are being pushed out through the negative contact and thus through the circuit by the voltage potential as would be expected. Battery manufacturers may regard

8320-422: The anode and the other the cathode according to the roles the electrodes play when the battery is discharged. This is despite the fact that the roles are reversed when the battery is charged. When this is done, "anode" simply designates the negative terminal of the battery and "cathode" designates the positive terminal. In a diode , the anode is the terminal represented by the tail of the arrow symbol (flat side of

8450-469: The anode combine with electrons supplied from the N-doped region, creating a depleted zone. As the P-doped layer supplies holes to the depleted region, negative dopant ions are left behind in the P-doped layer ('P' for positive charge-carrier ions). This creates a base negative charge on the anode. When a positive voltage is applied to anode of the diode from the circuit, more holes are able to be transferred to

8580-408: The anode comes from the oxidation reaction that takes place next to it. The cathode is in many ways the opposite of the anode. The name (also coined by Whewell) comes from the Greek words κάτω (kato), 'downwards' and ὁδός (hodós), 'a way'. It is the positive electrode, meaning the electrons flow from the electrical circuit through the cathode into the non-metallic part of the electrochemical cell. At

8710-401: The anode is the positive (+) electrode and the cathode the negative (−). The electrons enter the device through the cathode and exit the device through the anode. Many devices have other electrodes to control operation, e.g., base, gate, control grid. In a three-electrode cell, a counter electrode, also called an auxiliary electrode , is used only to make a connection to the electrolyte so that

8840-408: The anode is the positive terminal imposed by an external source of potential difference. The current through a recharging battery is opposite to the direction of current during discharge; in other words, the electrode which was the cathode during battery discharge becomes the anode while the battery is recharging. In battery engineering, it is common to designate one electrode of a rechargeable battery

8970-400: The anode of a galvanic cell , into an outside or external circuit connected to the cell. For example, the end of a household battery marked with a "+" is the cathode (while discharging). In both a galvanic cell and an electrolytic cell , the anode is the electrode at which the oxidation reaction occurs. In a galvanic cell the anode is the wire or plate having excess negative charge as

9100-518: The anode, anions (negative ions) are forced by the electrical potential to react chemically and give off electrons (oxidation) which then flow up and into the driving circuit. Mnemonics : LEO Red Cat (Loss of Electrons is Oxidation, Reduction occurs at the Cathode), or AnOx Red Cat (Anode Oxidation, Reduction Cathode), or OIL RIG (Oxidation is Loss, Reduction is Gain of electrons), or Roman Catholic and Orthodox (Reduction – Cathode, anode – Oxidation), or LEO

9230-411: The anode. It boasts a higher specific capacity than silicon, however, does come with the drawback of working with the highly unstable metallic lithium. Similarly to graphite anodes, dendrite formation is another major limitation of metallic lithium, with the solid electrolyte interphase being a major design challenge. In the end, if stabilized, metallic lithium would be able to produce batteries that hold

9360-481: The battery and posing a safety issue. Li 4 Ti 5 O 12 has the second largest market share of anodes, due to its stability and good rate capability, but with challenges such as low capacity. During the early 2000s, silicon anode research began picking up pace, becoming one of the decade's most promising candidates for future lithium-ion battery anodes. Silicon has one of the highest gravimetric capacities when compared to graphite and Li 4 Ti 5 O 12 as well as

9490-455: The cathode, the reduction reaction takes place with the electrons arriving from the wire connected to the cathode and are absorbed by the oxidizing agent . A primary cell is a battery designed to be used once and then discarded. This is due to the electrochemical reactions taking place at the electrodes in the cell not being reversible. An example of a primary cell is the discardable alkaline battery commonly used in flashlights. Consisting of

9620-429: The cathodic protection. Impressed current anodes are used in larger structures like pipelines, boats, city water tower, water heaters and more. The opposite of an anode is a cathode . When the current through the device is reversed, the electrodes switch functions, so the anode becomes the cathode and the cathode becomes anode, as long as the reversed current is applied. The exception is diodes where electrode naming

9750-415: The chemical driving forces are usually higher in magnitude than the mechanical energies, this is not true for Li-ion batteries. A study by Dr. Larché established a direct relation between the applied stress and the chemical potential of the electrode. Though it neglects multiple variables such as the variation of elastic constraints, it subtracts from the total chemical potential the elastic energy induced by

9880-426: The deformations in the lattice and, therefore stresses in the material. The origin of stresses may be due to geometric constraints in the electrode or inhomogeneous plating of the ion. This phenomenon is very concerning as it may lead to electrode fracture and performance loss. Thus, mechanical properties are crucial to enable the development of new electrodes for long lasting batteries. A possible strategy for measuring

10010-425: The depleted region, and this causes the diode to become conductive, allowing current to flow through the circuit. The terms anode and cathode should not be applied to a Zener diode , since it allows flow in either direction, depending on the polarity of the applied potential (i.e. voltage). In cathodic protection , a metal anode that is more reactive to the corrosive environment than the metal system to be protected

10140-607: The depletion region from the N-type side to the P-type side. The junction does not allow the flow of electrons in the opposite direction when the potential is applied in reverse, creating, in a sense, an electrical check valve . Another type of junction diode, the Schottky diode , is formed from a metal–semiconductor junction rather than a p–n junction, which reduces capacitance and increases switching speed. A semiconductor diode's behavior in

10270-460: The diode but with laser light would be the optical isolator , also known as an optical diode, that allows light to only pass in one direction. It uses a Faraday rotator as the main component. The first use for the diode was the demodulation of amplitude modulated (AM) radio broadcasts. The history of this discovery is treated in depth in the crystal detector article. In summary, an AM signal consists of alternating positive and negative peaks of

10400-411: The diode's forward voltage drop or just voltage drop , since a consequence of the steepness of the exponential is that a diode's voltage drop will not significantly exceed the threshold voltage under normal forward bias operating conditions. Datasheets typically quote a typical or maximum forward voltage (V F ) for a specified current and temperature (e.g. 20 mA and 25  ° C for LEDs), so

10530-585: The direction of flow of the electrons changes periodically , usually many times per second . Chemically modified electrodes are electrodes that have their surfaces chemically modified to change the electrode's physical , chemical , electrochemical , optical , electrical , and transportive properties. These electrodes are used for advanced purposes in research and investigation. Electrodes are used to provide current through nonmetal objects to alter them in numerous ways and to measure conductivity for numerous purposes. Examples include: Diode A diode

10660-461: The electrical circuit of an electrochemical cell (battery) into the non- metallic cell. The electrons then flow to the other side of the battery. Benjamin Franklin surmised that the electrical flow moved from positive to negative. The electrons flow away from the anode and the conventional current towards it. From both can be concluded that the charge of the anode is negative. The electron entering

10790-401: The electrode slurry. As can be seen above, the important properties of the electrode all have to do with the even distribution of the components of the electrode. Therefore, it is very important that the electrode slurry be as homogeneous as possible. Multiple procedures have been developed to improve this mixing stage and current research is still being done. A modern application of electrodes

10920-415: The electronic coupling constant describing the interaction between the two states (reactants and products) and g ( t ) {\displaystyle g(t)} being the line shape function . Taking the classical limit of this expression, meaning ℏ ω ≪ k T {\displaystyle \hbar \omega \ll kT} , and making some substitution an expression

11050-433: The evacuated tube due to being heated by a filament, so electrons can only enter the device from the external circuit through the heated electrode. Therefore, this electrode is permanently named the cathode, and the electrode through which the electrons exit the tube is named the anode. The polarity of voltage on an anode with respect to an associated cathode varies depending on the device type and on its operating mode. In

11180-409: The event of a later convention change it would have become West to East, so that the East electrode would not have been the 'way in' any more. Therefore, "eisode" would have become inappropriate, whereas "anode" meaning 'East electrode' would have remained correct with respect to the unchanged direction of the actual phenomenon underlying the current, then unknown but, he thought, unambiguously defined by

11310-458: The external voltage opposes the built-in potential, recombination can once again proceed, resulting in a substantial electric current through the p–n junction (i.e. substantial numbers of electrons and holes recombine at the junction) that increases exponentially with voltage. A diode's current–voltage characteristic can be approximated by four operating regions. From lower to higher bias voltages, these are: The Shockley ideal diode equation or

11440-424: The first semiconductor electronic devices . The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Today, most diodes are made of silicon , but other semiconducting materials such as gallium arsenide and germanium are also used. The obsolete thermionic diode is a vacuum tube with two electrodes ,

11570-446: The first superconducting diode effect without an external magnetic field was realized. At the time of their invention, asymmetrical conduction devices were known as rectifiers . In 1919, the year tetrodes were invented, William Henry Eccles coined the term diode from the Greek roots di (from δί ), meaning 'two', and ode (from οδός ), meaning 'path'. The word diode however

11700-478: The following century these electrodes were used to create and study the first Li-ion batteries. Li-ion batteries are very popular due to their great performance. Applications include mobile phones and electric cars. Due to their popularity, much research is being done to reduce the cost and increase the safety of Li-ion batteries. An integral part of the Li-ion batteries are their anodes and cathodes, therefore much research

11830-407: The following examples, the anode is negative in a device that provides power, and positive in a device that consumes power: In a discharging battery or galvanic cell (diagram on left), the anode is the negative terminal: it is where conventional current flows into the cell. This inward current is carried externally by electrons moving outwards. In a recharging battery, or an electrolytic cell ,

11960-414: The future. Since the later discovery of the electron , an easier to remember and more durably correct technically although historically false, etymology has been suggested: anode, from the Greek anodos , 'way up', 'the way (up) out of the cell (or other device) for electrons'. In electrochemistry , the anode is where oxidation occurs and is the positive polarity contact in an electrolytic cell . At

12090-404: The late 1940s due to selenium rectifier technology and then to semiconductor diodes during the 1960s. Today they are still used in a few high power applications where their ability to withstand transient voltages and their robustness gives them an advantage over semiconductor devices, and in musical instrument and audiophile applications. In 1874, German scientist Karl Ferdinand Braun discovered

12220-432: The least reactive materials for anodes. Platinum erodes very slowly compared to other materials, and graphite crumbles and can produce carbon dioxide in aqueous solutions but otherwise does not participate in the reaction. In a battery or galvanic cell , the anode is the negative electrode from which electrons flow out towards the external part of the circuit. Internally the positively charged cations are flowing away from

12350-644: The lion says GER (Losing electrons is Oxidation, Gaining electrons is Reduction). This process is widely used in metals refining. For example, in copper refining, copper anodes, an intermediate product from the furnaces, are electrolysed in an appropriate solution (such as sulfuric acid ) to yield high purity (99.99%) cathodes. Copper cathodes produced using this method are also described as electrolytic copper . Historically, when non-reactive anodes were desired for electrolysis, graphite (called plumbago in Faraday's time) or platinum were chosen. They were found to be some of

12480-452: The magnetic reference. In retrospect the name change was unfortunate, not only because the Greek roots alone do not reveal the anode's function any more, but more importantly because as we now know, the Earth's magnetic field direction on which the "anode" term is based is subject to reversals whereas the current direction convention on which the "eisode" term was based has no reason to change in

12610-410: The mechanical behavior of electrodes during operation is by using nanoindentation . The method is able to analyze how the stresses evolve during the electrochemical reactions, being a valuable tool in evaluating possible pathways for coupling mechanical behavior and electrochemistry. More than just affecting the electrode's morphology, stresses are also able to impact electrochemical reactions. While

12740-412: The metal point during manufacture by momentarily passing a relatively large current through the device. Point contact diodes generally exhibit lower capacitance, higher forward resistance and greater reverse leakage than junction diodes. A p–n junction diode is made of a crystal of semiconductor , usually silicon, but germanium and gallium arsenide are also used. Impurities are added to it to create

12870-451: The more straightforward term "eisode" (the doorway where the current enters). His motivation for changing it to something meaning 'the East electrode' (other candidates had been "eastode", "oriode" and "anatolode") was to make it immune to a possible later change in the direction convention for current , whose exact nature was not known at the time. The reference he used to this effect was the Earth's magnetic field direction, which at that time

13000-413: The most charge, while being the lightest. In recent years, researchers have conducted several studies on the use of single wall carbon nanotubes (SWCNTs) as conductive additives. These SWCNTs help to preserve electron conduction, ensure stable electrochemical reactions, and maintain uniform volume changes during cycling, effectively reducing anode pulverization. A common failure mechanism of batteries

13130-400: The negative electrode as the anode, particularly in their technical literature. Though from an electrochemical viewpoint incorrect, it does resolve the problem of which electrode is the anode in a secondary (or rechargeable) cell. Using the traditional definition, the anode switches ends between charge and discharge cycles. In electronic vacuum devices such as a cathode-ray tube , the anode

13260-421: The order of tens of nanoseconds to a few microseconds) may be required to remove the reverse recovery charge Q r from the diode. During this recovery time, the diode can actually conduct in the reverse direction. This might give rise to a large current in the reverse direction for a short time while the diode is reverse biased. The magnitude of such a reverse current is determined by the operating circuit (i.e.,

13390-445: The other direction. Therefore, the electrodes are named based on the direction of this "forward" current. In a diode the anode is the terminal through which current enters and the cathode is the terminal through which current leaves, when the diode is forward biased . The names of the electrodes do not change in cases where reverse current flows through the device. Similarly, in a vacuum tube only one electrode can emit electrons into

13520-455: The overall free energy of the reaction ( Δ G 0 {\displaystyle \Delta G^{0}} ). Δ G † = 1 4 λ ( Δ G 0 + λ ) 2 {\displaystyle \Delta G^{\dagger }={\frac {1}{4\lambda }}(\Delta G^{0}+\lambda )^{2}} In which the λ {\displaystyle \lambda }

13650-479: The peak inverse voltage rating for application in high voltage rectifiers), and required a large heat sink (often an extension of the diode's metal substrate ), much larger than the later silicon diode of the same current ratings would require. The vast majority of all diodes are the p–n diodes found in CMOS integrated circuits , which include two diodes per pin and many other internal diodes. The symbol used to represent

13780-482: The point of intersection (Q x ). One important thing to note, and was noted by Marcus when he came up with the theory, the electron transfer must abide by the law of conservation of energy and the Frank-Condon principle. Doing this and then rearranging this leads to the expression of the free energy activation ( Δ G † {\displaystyle \Delta G^{\dagger }} ) in terms of

13910-422: The pre-exponential factor which is usually experimentally determined, although a semi classical derivation provides more information as will be explained below. This classically derived result qualitatively reproduced observations of a maximum electron transfer rate under the conditions Δ G † = λ {\displaystyle \Delta G^{\dagger }=\lambda } . For

14040-517: The primary cell a secondary cell can be recharged. The first was the lead–acid battery , invented in 1859 by French physicist Gaston Planté . This type of battery is still the most widely used in among others automobiles. The cathode consists of lead dioxide (PbO2) and the anode of solid lead. Other commonly used rechargeable batteries are nickel–cadmium , nickel–metal hydride , and Lithium-ion . The last of which will be explained more thoroughly in this article due to its importance. Marcus theory

14170-892: The reactants and the products (the right and the left side of the chemical reaction) and therefore when their energies are the same and allow for electron transfer. As touched on before this must happen because only then conservation of energy is abided by. Skipping over a few mathematical steps the probability of electron transfer can be calculated (albeit quite difficult) using the following formula w E T = | J | 2 ℏ 2 ∫ − ∞ + ∞ d t e − i Δ E t / ℏ − g ( t ) {\displaystyle w_{ET}={\frac {|J|^{2}}{\hbar ^{2}}}\int _{-\infty }^{+\infty }dt\,e^{-i\Delta Et/\hbar -g(t)}} With J {\displaystyle J} being

14300-520: The same thing: reverse voltage protection, reverse polarity protection, and reverse battery protection. Diodes are frequently used to conduct damaging high voltages away from sensitive electronic devices. They are usually reverse-biased (non-conducting) under normal circumstances. When the voltage rises above the normal range, the diodes become forward-biased (conducting). For example, diodes are used in ( stepper motor and H-bridge ) motor controller and relay circuits to de-energize coils rapidly without

14430-429: The series resistance) and the diode is said to be in the storage-phase. In certain real-world cases it is important to consider the losses that are incurred by this non-ideal diode effect. However, when the slew rate of the current is not so severe (e.g. Line frequency) the effect can be safely ignored. For most applications, the effect is also negligible for Schottky diodes . The reverse current ceases abruptly when

14560-507: The stored charge is depleted; this abrupt stop is exploited in step recovery diodes for the generation of extremely short pulses. Normal (p–n) diodes, which operate as described above, are usually made of doped silicon or germanium . Before the development of silicon power rectifier diodes, cuprous oxide and later selenium was used. Their low efficiency required a much higher forward voltage to be applied (typically 1.4 to 1.7 V per "cell", with multiple cells stacked so as to increase

14690-423: The stress. μ = μ o + k ⋅ T ⋅ log ⁡ ( γ ⋅ x ) + Ω ⋅ σ {\displaystyle \mu =\mu ^{o}+k\cdot T\cdot \log(\gamma \cdot x)+\Omega \cdot \sigma } In this equation, μ represents the chemical potential, with μ° being its reference value. T stands for

14820-475: The system is a function of the translational, rotational, and vibrational coordinates of the reacting species and the molecules of the surrounding medium, collectively called the reaction coordinates. The abscissa the figure to the right represents these. From the classical electron transfer theory, the expression of the reaction rate constant (probability of reaction) can be calculated, if a non-adiabatic process and parabolic potential energy are assumed, by finding

14950-418: The table below. The surface topology of the electrode plays an important role in determining the efficiency of an electrode. The efficiency of the electrode can be reduced due to contact resistance . To create an efficient electrode it is therefore important to design it such that it minimizes the contact resistance. The production of electrodes for Li-ion batteries is done in various steps as follows: For

15080-460: The temperature and k the Boltzmann constant . The term γ inside the logarithm is the activity and x is the ratio of the ion to the total composition of the electrode. The novel term Ω is the partial molar volume of the ion in the host and σ corresponds to the mean stress felt by the system. The result of this equation is that diffusion, which is dependent on chemical potential, gets impacted by

15210-463: The thermionic diodes included in the tube (for example the 12SQ7 double diode triode ), and vacuum-tube rectifiers and gas-filled rectifiers were capable of handling some high-voltage/high-current rectification tasks better than the semiconductor diodes (such as selenium rectifiers ) that were available at that time. In 1873, Frederick Guthrie observed that a grounded, white-hot metal ball brought in close proximity to an electroscope would discharge

15340-436: The topology of the electrode. The properties required depend on the application and therefore there are many kinds of electrodes in circulation. The defining property for a material to be used as an electrode is that it be conductive . Any conducting material such as metals, semiconductors , graphite or conductive polymers can therefore be used as an electrode. Often electrodes consist of a combination of materials, each with

15470-417: The triangle), where conventional current flows into the device. Note the electrode naming for diodes is always based on the direction of the forward current (that of the arrow, in which the current flows "most easily"), even for types such as Zener diodes or solar cells where the current of interest is the reverse current. In vacuum tubes or gas-filled tubes , the anode is the terminal where current enters

15600-402: The tube. The word was coined in 1834 from the Greek ἄνοδος ( anodos ), 'ascent', by William Whewell , who had been consulted by Michael Faraday over some new names needed to complete a paper on the recently discovered process of electrolysis . In that paper Faraday explained that when an electrolytic cell is oriented so that electric current traverses the "decomposing body" (electrolyte) in

15730-822: The two most common being the EIA / JEDEC standard and the European Pro Electron standard: The standardized 1N-series numbering EIA370 system was introduced in the US by EIA/JEDEC (Joint Electron Device Engineering Council) about 1960. Most diodes have a 1-prefix designation (e.g., 1N4003). Among the most popular in this series were: 1N34A/1N270 (germanium signal), 1N914/ 1N4148 (silicon signal), 1N400x (silicon 1A power rectifier), and 1N580x (silicon 3A power rectifier). The JIS semiconductor designation system has all semiconductor diode designations starting with "1S". The European Pro Electron coding system for active components

15860-496: The user has a guarantee about when a certain amount of current will kick in. At higher currents, the forward voltage drop of the diode increases. For instance, a drop of 1 V to 1.5 V is typical at full rated current for silicon power diodes. (See also: Rectifier § Rectifier voltage drop ) However, a semiconductor diode's exponential current–voltage characteristic is really more gradual than this simple on–off action. Although an exponential function may appear to have

15990-403: The voltage polarity of electrodes but the direction of current through the electrode. An anode is an electrode of a device through which conventional current (positive charge) flows into the device from an external circuit, while a cathode is an electrode through which conventional current flows out of the device. If the current through the electrodes reverses direction, as occurs for example in

16120-477: The width of the depletion region (called the depletion width ) cannot grow without limit. For each electron–hole pair recombination made, a positively charged dopant ion is left behind in the N-doped region, and a negatively charged dopant ion is created in the P-doped region. As recombination proceeds and more ions are created, an increasing electric field develops through the depletion zone that acts to slow and then finally stop recombination. At this point, there

16250-442: The zinc coating becomes breached, either by cracking or physical damage. Once this occurs, corrosive elements act as an electrolyte and the zinc/iron combination as electrodes. The resultant current ensures that the zinc coating is sacrificed but that the base iron does not corrode. Such a coating can protect an iron structure for a few decades, but once the protecting coating is consumed, the iron rapidly corrodes. If, conversely, tin

16380-430: The zinc–copper electrode combination. Since then, many more batteries have been developed using various materials. The basis of all these is still using two electrodes, anodes and cathodes . 'Anode' was coined by William Whewell at Michael Faraday 's request, derived from the Greek words ἄνο (ano), 'upwards' and ὁδός (hodós), 'a way'. The anode is the electrode through which the conventional current enters from

16510-419: Was already in use, as were triode , tetrode , pentode , hexode , as terms of multiplex telegraphy . Although all diodes rectify , "rectifier" usually applies to diodes used for power supply , to differentiate them from diodes intended for small signal circuits. A thermionic diode is a thermionic-valve device consisting of a sealed, evacuated glass or metal envelope containing two electrodes :

16640-412: Was believed to be invariant. He fundamentally defined his arbitrary orientation for the cell as being that in which the internal current would run parallel to and in the same direction as a hypothetical magnetizing current loop around the local line of latitude which would induce a magnetic dipole field oriented like the Earth's. This made the internal current East to West as previously mentioned, but in

16770-502: Was devised by Alessandro Volta and was aptly named the Voltaic cell . This battery consisted of a stack of copper and zinc electrodes separated by brine -soaked paper disks. Due to fluctuation in the voltage provided by the voltaic cell, it was not very practical. The first practical battery was invented in 1839 and named the Daniell cell after John Frederic Daniell . It still made use of

16900-502: Was introduced in 1966 and comprises two letters followed by the part code. The first letter represents the semiconductor material used for the component (A = germanium and B = silicon) and the second letter represents the general function of the part (for diodes, A = low-power/signal, B = variable capacitance, X = multiplier, Y = rectifier and Z = voltage reference); for example: Other common numbering/coding systems (generally manufacturer-driven) include: In optics, an equivalent device for

#934065