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Basic knowledge of lithium battery

Basic knowledge of lithium battery

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  • Time of issue:2020-07-17
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(Summary description)BasicknowledgeoflithiumbatteryInanideallithiumionbattery,apartfromtheinsertionandextractionoflithiumionsbetweenthepositiveandnegativeelectrodes,noothersidereactionsoccur,andnoirreversibleconsumptionoflithiumionsoccurs.Theactuallithium-ionbatteryhassidereactionsandirreversibleconsumptionatalltimes,suchaselectrolytedecomposition,activematerialdissolution,metallithiumdeposition,etc.,butthedegreeisdifferent.Inactualbatterysystems,anysidereactionthatcanproduceorconsumelithiumionsorelectronsineachcyclemaycausechangesinbatterycapacitybalance.Oncethebatterycapacitybalancechanges,thischangeisirreversible,andcanbeaccumulatedthroughmultiplecycles,whichwillhaveaseriousimpactonbatteryperformance.(1)DissolutionofcathodematerialThedissolutionofMninspinelLiMn2O4isthemainreasonforthereversiblecapacitydegradationofLiMn204.TherearegenerallytwoexplanationsforthedissolutionmechanismofMn:redoxmechanismandionexchangemechanism. TheredoxmechanismreferstothehighconcentrationofMn3+attheendofthedischarge.TheMn+onthesurfaceofLiMn2O4willundergoadisproportionationreaction:2Mn3+(solid)Mn4+(solid)+Mn2+(liquid)Thedivalentmanganeseionsgeneratedbythedisproportionationreactiondissolveintheelectrolyte.TheionexchangemechanismreferstotheexchangeofLi+andH+onthesurfaceofthespinel,ThefinalformationofHMn204withnoelectrochemicalactivity.Xiaetal.’sresearchshowedthatthecapacitylosscausedbythedissolutionofmanganeseaccountedforthepercentageofthetotalbatterycapacitylossthatincreasedsignificantlyasthetemperatureincreased(from23%atroomtemperatureto34%at55°C)[14].(2)Phasechangeofcathodematerial[15]Therearetwotypesofphasechangesinlithium-ionbatteries:-isthephasechangeoftheelectrodematerialwhenlithiumionsarenormallyreleased;theotheristhephasechangeoftheelectrodematerialwhenoverchargeoroverdischarge.Forthefirsttypeofphasetransition,itisgenerallybelievedthatthenormaldeintercalationreactionoflithiumionsisalwaysaccompaniedbychangesinthemolarvolumeofthehoststructure,andatthesametime,stressisgeneratedinthematerial,whichcauseschangesinthehostlattice,andthesechangesreducetheparticles.Electrochemicalcontactbetweenparticlesandelectrodes.ThesecondtypeofphasetransitionistheJahn-Tellereffect.TheJahn-Tellereffectreferstotheexpansionandcontractionofthestructurecausedbytherepeatedintercalationanddeintercalationoflithiumions,whichcausestheoxygenoctahedrontodeviatefromthesphericalsymmetryandbecomeadeformedoctahedralconfiguration.TheirreversibletransformationofthespinelstructurecausedbytheJahn-TellereffectisalsooneofthemainreasonsforthecapacitydegradationofLiMn204.Duringdeepdischarge,theaveragevalenceofMnislowerthan3.5V,andthestructureofspinelchangesfromcubicphasetotetragonalphase.Thetetragonalcrystalhaslowrelativesymmetryandstrongdisorder,whichreducesthereversibilityofthedeintercalationoflithiumions,whichismanifestedastheattenuationofthereversiblecapacityofthecathodematerial. (3)Reductionofelectrolyte[15] Electrolytescommonlyusedinlithiumionbatteriesmainlyincludesolventscomposedofamixtureofvariousorganiccarbonates(suchasPC,EC,DMC,DEC,etc.)andelectrolytescomposedoflithiumsalts(suchasLiPF6,LiCIO4,LiAsF6,etc.).Underchargingconditions,theelectrolyteisunstabletothecarbon-containingelectrode,soareductionreactionwilloccur.Electrolytereductionconsumestheelectrolyteanditssolvent,whichhasanegativeimpactonbatterycapacityandcyclelife.Theresultinggaswillincreasetheinternalpressureofthebatteryandthreatenthesafetyofthesystem.(4)Volumelosscausedbyovercharge[15]Depositionofnegativeelectrodelithium:Whenovercharged,lithiumionsaredepositedonthesurfaceofthenegativeelectrodeactivematerial.Thedepositionoflithiumions-ontheonehand.Thenumberofreversiblelithiumionsisreduced.Ontheotherhand,thedepositedlithiummetalcaneasilyreactwiththesolventorsaltmoleculesintheelectrolytetogenerateLi2CO3,LiForothersubstances,whichcanblocktheelectrodeHole,eventuallyleadingtolossofcapacityandlife.Electrolyteoxidation:Theelectrolytecommonlyusedinlithium-ionbatteriesiseasilydecomposedtoforminsolubleLi2CO3andotherproductswhenovercharged,blockingthepolarporesandgeneratinggas,whichwillalsocausethelossofcapacityandcausesafetyhazards.Oxygendefectinthepositiveelectrode:ThereisatendencytoloseoxygeninthepositiveelectrodeLiMn204inthehigh-voltageregion,whichcausesoxygendefectsandleadstocapacityloss.(5)Self-dischargeMostofthecapacitylosscausedbytheself-dischargeoflithium-ionbatteriesisreversible,andonlyasmallpartisirreversible.Themainreasonsforirreversibleself-dischargeare:thelossoflithiumions(theformationofinfallibleLi2CO3andothersubstances);theelectrolyteoxidationproductblockstheelectrodemicroporesandincreasestheinternalresistance.  (6)FormationofinterfacefilmDuetotheirreversiblereactionbetweenlithiumionorelectrolyteandtheelectrode,szwillformasolidelectrolyteinterfacelayer(SEI)attheinterfacebetweenthenegativeelectrodeandtheelectrolyte.Thelossoflithiumionsduetotheformationofthispassivationfilmwillresultinachangeinthecapacitybalancebetweenthetwoelectrodes,andthecapacityofthebatterywilldecreaseinthefirstfewcycles.(7)CurrentcollectorThecur

Basic knowledge of lithium battery

(Summary description)BasicknowledgeoflithiumbatteryInanideallithiumionbattery,apartfromtheinsertionandextractionoflithiumionsbetweenthepositiveandnegativeelectrodes,noothersidereactionsoccur,andnoirreversibleconsumptionoflithiumionsoccurs.Theactuallithium-ionbatteryhassidereactionsandirreversibleconsumptionatalltimes,suchaselectrolytedecomposition,activematerialdissolution,metallithiumdeposition,etc.,butthedegreeisdifferent.Inactualbatterysystems,anysidereactionthatcanproduceorconsumelithiumionsorelectronsineachcyclemaycausechangesinbatterycapacitybalance.Oncethebatterycapacitybalancechanges,thischangeisirreversible,andcanbeaccumulatedthroughmultiplecycles,whichwillhaveaseriousimpactonbatteryperformance.(1)DissolutionofcathodematerialThedissolutionofMninspinelLiMn2O4isthemainreasonforthereversiblecapacitydegradationofLiMn204.TherearegenerallytwoexplanationsforthedissolutionmechanismofMn:redoxmechanismandionexchangemechanism. TheredoxmechanismreferstothehighconcentrationofMn3+attheendofthedischarge.TheMn+onthesurfaceofLiMn2O4willundergoadisproportionationreaction:2Mn3+(solid)Mn4+(solid)+Mn2+(liquid)Thedivalentmanganeseionsgeneratedbythedisproportionationreactiondissolveintheelectrolyte.TheionexchangemechanismreferstotheexchangeofLi+andH+onthesurfaceofthespinel,ThefinalformationofHMn204withnoelectrochemicalactivity.Xiaetal.’sresearchshowedthatthecapacitylosscausedbythedissolutionofmanganeseaccountedforthepercentageofthetotalbatterycapacitylossthatincreasedsignificantlyasthetemperatureincreased(from23%atroomtemperatureto34%at55°C)[14].(2)Phasechangeofcathodematerial[15]Therearetwotypesofphasechangesinlithium-ionbatteries:-isthephasechangeoftheelectrodematerialwhenlithiumionsarenormallyreleased;theotheristhephasechangeoftheelectrodematerialwhenoverchargeoroverdischarge.Forthefirsttypeofphasetransition,itisgenerallybelievedthatthenormaldeintercalationreactionoflithiumionsisalwaysaccompaniedbychangesinthemolarvolumeofthehoststructure,andatthesametime,stressisgeneratedinthematerial,whichcauseschangesinthehostlattice,andthesechangesreducetheparticles.Electrochemicalcontactbetweenparticlesandelectrodes.ThesecondtypeofphasetransitionistheJahn-Tellereffect.TheJahn-Tellereffectreferstotheexpansionandcontractionofthestructurecausedbytherepeatedintercalationanddeintercalationoflithiumions,whichcausestheoxygenoctahedrontodeviatefromthesphericalsymmetryandbecomeadeformedoctahedralconfiguration.TheirreversibletransformationofthespinelstructurecausedbytheJahn-TellereffectisalsooneofthemainreasonsforthecapacitydegradationofLiMn204.Duringdeepdischarge,theaveragevalenceofMnislowerthan3.5V,andthestructureofspinelchangesfromcubicphasetotetragonalphase.Thetetragonalcrystalhaslowrelativesymmetryandstrongdisorder,whichreducesthereversibilityofthedeintercalationoflithiumions,whichismanifestedastheattenuationofthereversiblecapacityofthecathodematerial. (3)Reductionofelectrolyte[15] Electrolytescommonlyusedinlithiumionbatteriesmainlyincludesolventscomposedofamixtureofvariousorganiccarbonates(suchasPC,EC,DMC,DEC,etc.)andelectrolytescomposedoflithiumsalts(suchasLiPF6,LiCIO4,LiAsF6,etc.).Underchargingconditions,theelectrolyteisunstabletothecarbon-containingelectrode,soareductionreactionwilloccur.Electrolytereductionconsumestheelectrolyteanditssolvent,whichhasanegativeimpactonbatterycapacityandcyclelife.Theresultinggaswillincreasetheinternalpressureofthebatteryandthreatenthesafetyofthesystem.(4)Volumelosscausedbyovercharge[15]Depositionofnegativeelectrodelithium:Whenovercharged,lithiumionsaredepositedonthesurfaceofthenegativeelectrodeactivematerial.Thedepositionoflithiumions-ontheonehand.Thenumberofreversiblelithiumionsisreduced.Ontheotherhand,thedepositedlithiummetalcaneasilyreactwiththesolventorsaltmoleculesintheelectrolytetogenerateLi2CO3,LiForothersubstances,whichcanblocktheelectrodeHole,eventuallyleadingtolossofcapacityandlife.Electrolyteoxidation:Theelectrolytecommonlyusedinlithium-ionbatteriesiseasilydecomposedtoforminsolubleLi2CO3andotherproductswhenovercharged,blockingthepolarporesandgeneratinggas,whichwillalsocausethelossofcapacityandcausesafetyhazards.Oxygendefectinthepositiveelectrode:ThereisatendencytoloseoxygeninthepositiveelectrodeLiMn204inthehigh-voltageregion,whichcausesoxygendefectsandleadstocapacityloss.(5)Self-dischargeMostofthecapacitylosscausedbytheself-dischargeoflithium-ionbatteriesisreversible,andonlyasmallpartisirreversible.Themainreasonsforirreversibleself-dischargeare:thelossoflithiumions(theformationofinfallibleLi2CO3andothersubstances);theelectrolyteoxidationproductblockstheelectrodemicroporesandincreasestheinternalresistance.  (6)FormationofinterfacefilmDuetotheirreversiblereactionbetweenlithiumionorelectrolyteandtheelectrode,szwillformasolidelectrolyteinterfacelayer(SEI)attheinterfacebetweenthenegativeelectrodeandtheelectrolyte.Thelossoflithiumionsduetotheformationofthispassivationfilmwillresultinachangeinthecapacitybalancebetweenthetwoelectrodes,andthecapacityofthebatterywilldecreaseinthefirstfewcycles.(7)CurrentcollectorThecur

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Basic knowledge of lithium battery
In an ideal lithium ion battery, apart from the insertion and extraction of lithium ions between the positive and negative electrodes, no other side reactions occur, and no irreversible consumption of lithium ions occurs. The actual lithium-ion battery has side reactions and irreversible consumption at all times, such as electrolyte decomposition, active material dissolution, metal lithium deposition, etc., but the degree is different. In actual battery systems, any side reaction that can produce or consume lithium ions or electrons in each cycle may cause changes in battery capacity balance. Once the battery capacity balance changes, this change is irreversible, and can be accumulated through multiple cycles, which will have a serious impact on battery performance.
(1) Dissolution of cathode material
The dissolution of Mn in spinel LiMn2O4 is the main reason for the reversible capacity degradation of LiMn204. There are generally two explanations for the dissolution mechanism of Mn: redox mechanism and ion exchange mechanism.
 
The redox mechanism refers to the high concentration of Mn3+ at the end of the discharge. The Mn+ on the surface of LiMn2O4 will undergo a disproportionation reaction: 2Mn3+ (solid) Mn4+ (solid) +Mn2+ (liquid) The divalent manganese ions generated by the disproportionation reaction dissolve in the electrolyte. The ion exchange mechanism refers to the exchange of Li+ and H+ on the surface of the spinel,
The final formation of HMn204 with no electrochemical activity. Xia et al.’s research showed that the capacity loss caused by the dissolution of manganese accounted for the percentage of the total battery capacity loss that increased significantly as the temperature increased (from 23% at room temperature to 34% at 55°C) [14].
(2) Phase change of cathode material[15]
There are two types of phase changes in lithium-ion batteries:-is the phase change of the electrode material when lithium ions are normally released; the other is the phase change of the electrode material when overcharge or overdischarge. For the first type of phase transition, it is generally believed that the normal deintercalation reaction of lithium ions is always accompanied by changes in the molar volume of the host structure, and at the same time, stress is generated in the material, which causes changes in the host lattice, and these changes reduce the particles. Electrochemical contact between particles and electrodes. The second type of phase transition is the Jahn-Teller effect. The Jahn-Teller effect refers to the expansion and contraction of the structure caused by the repeated intercalation and deintercalation of lithium ions, which causes the oxygen octahedron to deviate from the spherical symmetry and become a deformed octahedral configuration. The irreversible transformation of the spinel structure caused by the Jahn-Teller effect is also one of the main reasons for the capacity degradation of LiMn204. During deep discharge, the average valence of Mn is lower than 3.5V, and the structure of spinel changes from cubic phase to tetragonal phase. The tetragonal crystal has low relative symmetry and strong disorder, which reduces the reversibility of the deintercalation of lithium ions, which is manifested as the attenuation of the reversible capacity of the cathode material.
 
(3) Reduction of electrolyte[15]
 
Electrolytes commonly used in lithium ion batteries mainly include solvents composed of a mixture of various organic carbonates (such as PC, EC, DMC, DEC, etc.) and electrolytes composed of lithium salts (such as LiPF6, LiCIO4, LiAsF6, etc.). Under charging conditions, the electrolyte is unstable to the carbon-containing electrode, so a reduction reaction will occur. Electrolyte reduction consumes the electrolyte and its solvent, which has a negative impact on battery capacity and cycle life. The resulting gas will increase the internal pressure of the battery and threaten the safety of the system.
(4) Volume loss caused by overcharge [15]
Deposition of negative electrode lithium: When overcharged, lithium ions are deposited on the surface of the negative electrode active material. The deposition of lithium ions-on the one hand. The number of reversible lithium ions is reduced. On the other hand, the deposited lithium metal can easily react with the solvent or salt molecules in the electrolyte to generate Li2CO3, LiF or other substances, which can block the electrode Hole, eventually leading to loss of capacity and life. Electrolyte oxidation: The electrolyte commonly used in lithium-ion batteries is easily decomposed to form insoluble Li2CO3 and other products when overcharged, blocking the polar pores and generating gas, which will also cause the loss of capacity and cause safety hazards. Oxygen defect in the positive electrode: There is a tendency to lose oxygen in the positive electrode LiMn204 in the high-voltage region, which causes oxygen defects and leads to capacity loss.
(5) Self-discharge
Most of the capacity loss caused by the self-discharge of lithium-ion batteries is reversible, and only a small part is irreversible. The main reasons for irreversible self-discharge are: the loss of lithium ions (the formation of infallible Li2CO3 and other substances); the electrolyte oxidation product blocks the electrode micropores and increases the internal resistance.
 
 
(6) Formation of interface film
Due to the irreversible reaction between lithium ion or electrolyte and the electrode, sz will form a solid electrolyte interface layer (SEI) at the interface between the negative electrode and the electrolyte. The loss of lithium ions due to the formation of this passivation film will result in a change in the capacity balance between the two electrodes, and the capacity of the battery will decrease in the first few cycles.
(7) Current collector
The current collector materials in lithium-ion batteries are commonly copper and aluminum, both of which are prone to corrosion. The corrosion of the current collector will increase the internal resistance of the battery and cause a loss of capacity. Why use copper foil for the negative electrode and aluminum foil for the positive electrode
1. Both are used as current collectors because they have good electrical conductivity, soft texture (maybe it will also be good for bonding), relatively common and cheaper, and both surfaces can form one-layer oxide protection membrane.
2. The oxide layer on the copper surface is a semiconductor, and the electrons are conductive, the oxide layer is too thick, and the resistance is large; while the oxide layer on the aluminum surface is an insulator, the oxide layer cannot conduct electricity, but because it is very thin, the electron conduction is realized through the tunnel effect. If the oxide layer is thick, the conductivity of the aluminum foil is poor and even insulated. --Generally, the current collector should be cleaned on the surface before use. On the one hand, it can wash away the oil stains and at the same time remove the thick oxide layer.
3. The anode potential is high, and the thin aluminum oxide layer is very dense, which can prevent the current collector from oxidizing. The copper foil oxide layer is looser. In order to prevent its oxidation, the potential is better. At the same time, Li is difficult to form a lithium intercalation alloy with Cu at low potentials. However, if the copper surface is oxidized a lot, Li will oxidize at a slightly higher potential. Lithium intercalation occurs in copper. AL foil cannot be used as a negative electrode, and LiAl alloying will occur at low potentials.
4. The current collector must be pure in composition. The impure composition of AL will cause the surface film to be not dense and pitting corrosion, and even the destruction of the surface film leads to the formation of LiAI alloy. The copper mesh is cleaned with hydrogen sulfate and then cleaned with deionized water and then baked. The aluminum mesh is cleaned with ammonia salt and then cleaned with deionized water and then baked. The spray mesh has good conductivity.
 
Basic knowledge of lithium ion batteries
The first section of the basic knowledge of lithium-ion batteries
Generally speaking, lithium-ion batteries have three parts:
1. Lithium ion battery
2. Protection circuit (PCM)
3. The shell is the plastic shell
 
Classification of batteries
From the perspective of the cooperation of lithium-ion batteries with mobile phones, they are generally divided into external batteries and internal batteries. This name is easy to understand that external batteries are directly installed on the back of the hand, such as: MOTOROLA191, SAMSUNG series, etc.; and internal batteries After it is installed in the mobile phone, there is another shell to buckle it into the mobile phone battery, such as: MOTOROLA 998 8088, most of NOKIA models
1. External battery
There are two types of packaging for external batteries: ultrasonic welding and snapping:
1.1 Ultrasonic welding shell.
The battery shells of this type of packaging are divided into bottom shells. The material--is generally ABS+PC. The shell is generally treated with oil injection. Representative models are: MOTOROLA 191, SAMSUNG series. The original battery shell is treated with oil injection. Long-term use-generally does not fray, but some brands of batteries or parallel batteries are used. In the past few days, the casing began to fall off after spraying oil. The reason is that the casing of mobile phone batteries is cheaper.
 
The cost of oil injection treatment is generally several times that of the shell (a little better), and there are generally three processes in this treatment: spray varnish (priming), spray (form color), and spray bright oil (the order should be In this way, if I remember correctly), and some manufacturers have omitted the first and third processes in order to reduce costs, so the cost is very low.
Ultrasonic welding machine
Its role is:
The relatively good domestic ultrasonic welding machine in the industry should be produced by Shenzhen Keweixin Electromechanical Company. Welding with a good ultrasonic welding machine is not enough, whether it can be welded OK, it is also very dependent on the shell material and welding machine parameter settings. The big relationship is that the shell is mainly related to the doping of the nozzle material of the manufacturer, and the parameter setting needs to be explored by yourself. Since it involves some technical data of the company, it is inconvenient to talk more here.
1.2 Snap-in
The principle of the snap-on battery is that the bottom shell is designed to form a snap-on type. One is generally disposable. If the card is forcibly opened by the user, it cannot be restored, but this is not very difficult for the manufacturer. (After the card is closed, fold it again), its representative models are: Ericsson 788, MOTOROLA V66.
2. Built-in battery
There are also two types of sealing for the built-in battery. Ultrasonic welding and labeling (using the trademark to wrap all the batteries) Ultrasonic welding batteries mainly include: NOKIA 8210, 8250, 8310, 7210, etc. There are many labeled batteries, such as the first two MOTO998, which is very young in the year, is 8088.
 
The second section of the basic knowledge of lithium ion batteries
Lithium-ion batteries are a new type of battery energy source. They do not contain metallic lithium. During charging and discharging, only lithium ions move back and forth between the positive and negative electrodes, and the electrodes and electrolyte do not participate in the reaction. The energy capacity density of lithium ion batteries can reach 300Wh/L, and the weight capacity density can reach 125Wh/L.
1. Principle of battery
The reaction mechanism of lithium ion batteries is that as the charge and discharge progress, lithium ions are inserted and extracted between the positive and negative electrodes, and shuttle inside the battery without the presence of metal lithium, so the lithium ion batteries are more safe and stable. The reaction schematic diagram and basic reaction formula are as follows:
2, the structure of the battery
The positive electrode of the battery core is LiCoO2 plus conductive agent and binder, which is coated on aluminum foil to form a positive plate. The negative electrode is layered graphite plus conductive agent and binder coated on the copper foil base tape. At present, the more advanced negative electrode layered graphite Nano carbon has been adopted for the particles. According to the above reaction mechanism, LiCoO2, LiNiO2, LiMn2O2 are used as the positive electrode. LiCoO2 is originally a crystal type with a very stable seed layer structure, but when XLi is removed from LiCoO2, its structure may change, but whether it changes depends on X the size of. Through research, it is found that when X>0.5, the structure of Li1-XCoO2 is extremely unstable, the crystal form collapses, and its external appearance is the overwhelming end of the cell. Therefore, the X value in Li1-XCoO2 should be controlled by limiting the charging voltage during the use of the battery. Generally, the charging voltage is not greater than 4.2V and X is less than 0.5. At this time, the crystal form of Li1-XCoO2 is still stable. The negative electrode C6 has its own characteristics. After the first formation, the Li in the positive electrode LiCoO2 is charged into the negative electrode C6. When discharging, Li returns to the positive electrode LiCoO2, but a part of Li must remain in the negative electrode C6 after the formation. In order to ensure the normal insertion of Li in the next charge and discharge, otherwise the cell will be overwhelmed very short. In order to ensure that a part of Li remains in the negative electrode C6, it is generally achieved by limiting the lower limit voltage of discharge. Therefore, the upper limit voltage of safe charging of lithium batteries is ≤4.2V, and the lower limit voltage of discharge is ≥2.5V.
 
 

 

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