Lithium-ion batteries are the fastest-growing secondary batteries after nickel-cadmium and nickel-hydrogen batteries. Its high-energy properties make its future look bright. However, lithium-ion batteries are not perfect, and their biggest problem is the stability of their charge-discharge cycles. This paper summarizes and analyzes the possible reasons for the capacity fading of Li-ion batteries, including overcharge, electrolyte decomposition and self-discharge.

Lithium-ion batteries have different intercalation energies when intercalation reactions occur between the two electrodes, and in order to obtain the best performance of the battery, the capacity ratio of the two host electrodes should maintain a balanced value.

In lithium-ion batteries, the capacity balance is expressed as the mass ratio of the positive electrode to the negative electrode,

Izvi zvinoreva: γ=m+/m-=ΔxC-/ΔyC+

In the above formula, C refers to the theoretical coulombic capacity of the electrode, and Δx and Δy refer to the stoichiometric number of lithium ions embedded in the negative electrode and the positive electrode, respectively. It can be seen from the above formula that the required mass ratio of the two poles depends on the corresponding Coulomb capacity of the two poles and the number of their respective reversible lithium ions.

mufananidzo

Kazhinji kutaura, diki diki reshiyo inotungamira kune isina kukwana kushandiswa kwezvinhu zvisina kunaka electrode; chiyero chikuru chehuwandu chinogona kukonzera njodzi yekuchengetedza nekuda kwekuwedzerwa kweiyo yakaipa electrode. Muchidimbu, pachiyero chakagadziriswa misara, kuita kwebhatiri ndiko kwakanyanya kunaka.

Kune yakanakira Li-ion bhatiri system, chiyero chesimba hachichinje panguva yekutenderera kwayo, uye yekutanga kugona mune imwe neimwe kutenderera kune imwe kukosha, asi iyo chaiyo mamiriro akanyanya kuoma. Chero maitiro epadivi anogona kugadzira kana kushandisa lithium ions kana maerekitironi zvinogona kutungamira kukuchinja kwebhatiri renji. Kana huwandu hwebhatiri hwachinja, shanduko iyi haidzokerike uye inogona kuunganidzwa kuburikidza neakawanda, zvichikonzera kushanda kwebhatiri. Serious impact. Mumabhatiri e-lithium-ion, kuwedzera kune maitiro e-redox anoitika kana lithium ion ikadzivirirwa, kunewo nhamba huru yemaitiro emativi, akadai se electrolyte decomposition, active material dissolution, uye metallic lithium deposition.

Chikonzero 1: Kuwandisa

1. Overcharge reaction yegraphite negative electrode:

Kana bhatiri rawandisa, lithium ions inodzikiswa zviri nyore uye kuiswa pamusoro peiyo negative electrode:

mufananidzo

Iyo yakaiswa lithium inopfeka iyo yakaipa electrode pamusoro, ichivharira kupindirana kwe lithium. Izvi zvinoguma nekudzikiswa kwekuburitsa uye kurasikirwa kwesimba nekuda kwe:

①Deredzai huwandu hweinogona kushandiswazve lithium;

②Iyo yakaiswa simbi lithium inopindirana ne solvent kana inotsigira electrolyte kuumba Li2CO3, LiF kana zvimwe zvigadzirwa;

③ Metal lithium inowanzoumbwa pakati pe electrode yakaipa uye separator, iyo inogona kuvhara pores yemuparadzi uye kuwedzera kupikisa kwemukati kwebheteri;

④ Nekuda kweiyo inoshanda hunhu hwe lithium, zviri nyore kuita ne electrolyte uye kushandisa iyo electrolyte, zvichikonzera kuderedzwa kwekubuda zvakanaka uye kurasikirwa kwesimba.

Kuchaja nekukurumidza, density iripo yakakura kwazvo, iyo negative electrode inopolarized zvakanyanya, uye kuiswa kwelithium kuchave kuri pachena. Izvi zvingangoitika kana iyo yakanaka electrode inoshanda zvinhu yakawandisa maererano neiyo negative electrode inoshanda zvinhu. Nekudaro, kana iri iyo yakakwira yekuchaja mwero, deposition yesimbi lithium inogona kuitika kunyangwe chiyero chezvakanaka uye zvisina kunaka zvinhu zvinoshanda zvakajairika.

2. Positive electrode overcharge reaction

When the ratio of positive electrode active material to negative electrode active material is too low, positive electrode overcharge is likely to occur.

Kurasikirwa kwesimba kunokonzerwa nekuwedzeredza kweiyo yakanaka electrode kunonyanya kukonzerwa nekugadzirwa kwezvinhu zvine electrochemically inert (senge Co3O4, Mn2O3, nezvimwewo), izvo zvinoparadza chiyero chesimba pakati pemagetsi, uye kurasikirwa kwesimba hakuchinjiki.

(1) LiyCoO2

LiyCoO2→(1-y)/3[Co3O4＋O2(g)]＋yLiCoO2 y<0.4

Panguva imwecheteyo, iyo okisijeni inogadzirwa nekuparara kweiyo yakanaka electrode zvinhu muyakavharwa lithium-ion bhatiri inounganidza panguva imwe chete nekuti hapana recombination reaction (yakadai sechizvarwa cheH2O) uye gasi rinopisa rinogadzirwa nekuparara. ye electrolyte, uye mhedzisiro yacho ichave isingafungidzike.

(2) λ-MnO2

Iyo lithium-manganese reaction inoitika kana iyo lithium-manganese oxide yakasvibiswa zvachose: λ-MnO2→Mn2O3+O2(g)

3. Iyo electrolyte inoiswa oxidized kana yakawandisa

Kana dzvinyiriro yakakwira kupfuura 4.5V, iyo electrolyte inozoiswa oxidized kugadzira zvisinganyungudika (seLi2Co3) nemagasi. Aya ma-insolubles anovhara ma micropores e electrode uye anotadzisa kutama kwe lithium ions, zvichikonzera kurasikirwa kwesimba panguva yebhasikoro.

Zvinhu zvinokanganisa chiyero che oxidation:

The surface area of ​​the positive electrode material

Ikozvino muunganidzi zvinhu

Added conductive agent (carbon black, etc.)

The type and surface area of ​​carbon black

Pakati peanowanzo shandiswa maelectrolyte, EC/DMC inoonekwa seine yakanyanya oxidation kuramba. Iyo electrochemical oxidation process yemhinduro inowanzo ratidzwa se: mhinduro → oxidation chigadzirwa (gasi, mhinduro uye yakasimba nyaya)+ne-

Iko oxidation yechero solvent ino wedzera chiyero che electrolyte, kuderedza kugadzikana kwe electrolyte, uye pakupedzisira kukanganisa kugona kwebhatiri. Tichifunga kuti ishoma ye electrolyte inopedzwa pese painochajwa, electrolyte yakawanda inodiwa panguva yekubatanidza bhatiri. Kune chigadziko chinogara chiripo, izvi zvinoreva kuti chidimbu chidiki chechinhu chinoshanda chinotakurwa, izvo zvinoguma nekuderera kwesimba rekutanga. Mukuwedzera, kana chigadzirwa chakasimba chikagadzirwa, firimu rekufambisa richaumbwa pamusoro pe electrode, iyo inowedzera polarization yebhatiri uye kuderedza kubuda kwebhatiri.

Chikonzero 2: Electrolyte decomposition (kuderedza)

Ndinoora pa electrode

1. The electrolyte is decomposed on the positive electrode:

Iyo electrolyte ine solvent uye electrolyte inotsigira. Mushure mokunge cathode yakaora, zvigadzirwa zvisingasviki zvakadai seLi2Co3 neLiF zvinowanzogadzirwa, izvo zvinoderedza simba rebhatiri nekuvhara pores ye electrode. Iyo electrolyte yekudzikisa maitiro ichava nemhedzisiro yakaipa pakukwanisa uye kutenderera hupenyu hwebhatiri. Iyo gasi inogadzirwa nekudzikisa inogona kuwedzera kudzvinyirira kwemukati kwebhatiri, izvo zvinogona kutungamirira kumatambudziko ekuchengetedza.

Iyo yakanaka electrode decomposition voltage inowanzopfuura 4.5V (vs. Li / Li +), saka haigoni kuora nyore pane electrode yakanaka. Pane zvinopesana, iyo electrolyte inoora nyore nyore pane iyo yakaipa electrode.

2. The electrolyte is decomposed on the negative electrode:

Iyo electrolyte haina kugadzikana pane graphite uye imwe lithium-yakaiswa kabhoni anode, uye zviri nyore kuita kuti igadzire isingachinjiki simba. Panguva yekutanga kuchaja uye kubuda, kuparara kwe electrolyte kuchaita firimu rekufambisa pamusoro pe electrode, uye passivation firimu inogona kuparadzanisa electrolyte kubva kucarbon negative electrode kudzivirira kuwedzera kuparara kwe electrolyte. Nokudaro, kugadzikana kwemaitiro e carbon anode kunochengetwa. Pasi pemamiriro ezvinhu akanaka, kuderedzwa kwe electrolyte kunogumira kune passivation firimu yekugadzira nhanho, uye iyi nzira haiitike kana kutenderera kwakagadzikana.

Kugadzirwa kwefirimu yepassivation

Kuderedzwa kwemunyu we electrolyte kunotora chikamu mukuumbwa kwefirimu yepassivation, iyo inobatsira pakudzikamisa kwefirimu rekupfuura, asi.

(1) The insoluble matter produced by the reduction will have an adverse effect on the solvent reduction product;

(2) Kusanganiswa kwe electrolyte kunoderera apo munyu we electrolyte wakaderera, izvo zvinozoguma zvichiita kuti kurasikirwa kwebhatiri simba (LiPF6 yakaderedzwa kuita LiF, LixPF5-x, PF3O uye PF3);

(3) Kuumbwa kwefirimu rekufambisa kunoshandisa lithium ions, izvo zvichaita kuti kusaenzana kwesimba pakati pema electrode maviri kuderedza huwandu hwebhatiri rose.

(4) Kana pane kuputika pafirimu yekufambisa, mamorekuru anonyungudutsa anogona kupinda uye kuomesa firimu rekufambisa, iro risingangopei lithium yakawanda, asiwo rinogona kuvhara ma micropores pa carbon surface, zvichiita kuti kusakwanisa kwe lithiamu kuiswa uye extracted. , zvichikonzera kurasikirwa kwesimba kusingadzoreki. Kuwedzera mamwe madhipatimendi ekuwedzera kune electrolyte, senge CO2, N2O, CO, SO2, nezvimwewo, inogona kukurumidza kuumbwa kweiyo passivation firimu uye inhibisa kubatanidzwa uye kuparara kweiyo solvent. Kuwedzerwa kwekorona ether organic additives kunewo maitiro akafanana. 12 korona uye 4 ethers ndiyo yakanakisisa.

Zvinhu zvekurasikirwa kwehuwandu hwefirimu:

(1) Rudzi rwekabhoni inoshandiswa mukuita;

(2) Electrolyte kuumbwa;

(3) Additives in electrodes or electrolytes.

Blyr anotenda kuti iyo ion inotsinhanisa maitiro inofambira mberi kubva pamusoro peiyo inoshanda chinhu chimedu kusvika pakati payo, nhanho nyowani inoumbwa inoviga iyo yekutanga inoshanda zvinhu, uye firimu rinopfuura rine yakaderera ionic uye yemagetsi conductivity inoumbwa pamusoro pechinhu, saka. iyo spinel mushure mekuchengetedza Greater polarization kupfuura isati yachengetwa.

Zhang akawana kuti kushorwa kwepasi passivation layer kwakawedzera uye iyo interfacial capacitance yakadzikira nekuwedzera kwenhamba yekutenderera. Zvinotaridza kuti ukobvu hwepassivation layer hunowedzera nehuwandu hwema cycles. Kunyungudika kwemanganese uye kuparara kweelectrolyte kunotungamirira mukuumbwa kwemafirimu ekufambisa, uye mamiriro ekushisa kwepamusoro anowedzera kufambira mberi kwemaitiro aya. Izvi zvichawedzera kusangana kwekupokana pakati peanoshanda zvinhu zvimedu uye Li + migration kuramba, nekudaro zvichiwedzera polarization yebhatiri, isina kukwana kuchaja uye kuburitsa, uye kuderedzwa kugona.

II Kuderedza Mechanism yeElectrolyte

Iyo electrolyte inowanzova neokisijeni, mvura, kabhoni dhaibhorosi uye kumwe kusvibiswa, uye maitiro eredox anoitika panguva yekuchaja nekuburitsa bhatiri.

Nzira yekudzikisa ye electrolyte inosanganisira zvinhu zvitatu: kuderedza solvent, kuderedza electrolyte uye kuderedza kusachena:

1. Kuderedza kunyungudutsa

Kudzikiswa kwePC neEC kunosanganisira one-electron reaction uye maviri-electron reaction process, uye maviri-electron reaction mafomu Li2CO3:

Fong et al. believed that during the first discharge process, when the electrode potential was close to 0.8V (vs. Li/Li+), the electrochemical reaction of PC/EC occurred on graphite to generate CH=CHCH3(g)/CH2=CH2( g) and LiCO3(s), leading to irreversible capacity loss on graphite electrodes.

Aurbach et al. conducted extensive research on the reduction mechanism and products of various electrolytes on lithium metal electrodes and carbon-based electrodes, and found that the one-electron reaction mechanism of PC produces ROCO2Li and propylene. ROCO2Li is very sensitive to trace water. The main products are Li2CO3 and propylene in the presence of trace water, but no Li2CO3 is produced under dry conditions.

Kudzorerwa kweDEC:

Ein-Eli Y yakashuma kuti electrolyte yakasanganiswa nediethyl carbonate (DEC) uye dimethyl carbonate (DMC) ichaita shanduko mubhatiri kuti ibudise ethyl methyl carbonate (EMC), iyo inokonzera kurasikirwa kwesimba. zvimwe pesvedzero.

2. Electrolyte kuderedza

The reduction reaction of the electrolyte is generally considered to be involved in the formation of the carbon electrode surface film, so its type and concentration will affect the performance of the carbon electrode. In some cases, the reduction of the electrolyte contributes to the stabilization of the carbon surface, which can form the desired passivation layer.

Zvinowanzotendwa kuti inotsigira electrolyte iri nyore kudzikisira pane inonyungudutsa, uye chigadzirwa chekudzikisa chinosanganiswa muinegetive electrode deposition firimu uye inokanganisa kugona kwebhatiri. Mazhinji maitiro ekuderedza maitiro ekutsigira electrolyte ndeaya anotevera:

3. Kuderedza kusachena

(1) Kana mvura iri mu electrolyte yakanyanyisa, LiOH (s) uye Li2O deposits ichaumbwa, izvo zvisingakodzeri kuiswa kwe lithium ions, zvichiita kuti simba rirege kudzoka shure:

H2O＋e→OH-＋1/2H2

OH-＋Li+→LiOH(s)

LiOH+Li++e-→Li2O(s)+1/2H2

Iyo LiOH (s) inogadzirwa inoiswa pamusoro pe electrode, ichiita firimu repamusoro rine kupikisa kwakanyanya, izvo zvinotadzisa Li + kupindirana mu graphite electrode, zvichikonzera kurasikirwa kwesimba kusingadzoreki. Mvura shoma shoma (100-300 × 10-6) musolvent haina simba pakushanda kwe graphite electrode.

(2) Iyo CO2 mune solvent inogona kuderedzwa pane iyo yakaipa electrode kuti iite CO uye LiCO3 (s):

2CO2+2e-+2Li+→Li2CO3+CO

CO will increase the internal pressure of the battery, and Li2CO3(s) will increase the internal resistance of the battery and affect the battery performance.

(3) Kuvapo kweokisijeni mune inonyungudutsa ichaitawo Li2O

1/2O2+2e-+2Li+→Li2O

Nekuda kwekuti mutsauko unokwanisa pakati pesimbi lithium uye yakanyatsopindirana kabhoni idiki, kudzikiswa kwe electrolyte pacarbon kwakafanana nekudzikiswa kwelithium.

Chikonzero 3: Kuzvibvisa wega

Kuzviburitsa (self discharge) zvinoreva chiitiko chekuti bhatiri rinorasikirwa nekugona kwaro kana risiri kushandiswa. Li-ion bhatiri yekuzviburitsa inotungamira mukurasikirwa kwehuwandu muzviitiko zviviri:

Imwe ndeyekudzoserwa kugona kurasikirwa;

Chechipiri kurasikirwa kwesimba risingadzoreki.

Kudzoreredzwa kurasikirwa kwesimba kunoreva kuti iyo yakarasika simba inogona kudzoserwa panguva yekuchaja, nepo isingadzokerike kurasikirwa kwesimba kwakapesana. Maelectrodes akanaka uye asina kunaka anogona kuita se microbattery ine electrolyte munzvimbo yakachajiswa, zvichiita kuti lithium ion intercalation uye deintercalation, uye intercalation uye deintercalation yakanaka uye yakaipa electrodes. Iyo yakamisikidzwa lithium ion inongobatana chete neiyo lithium ions ye electrolyte, saka kugona kweiyo yakanaka uye yakaipa electrode haina kuenzana, uye ichi chikamu chekurasikirwa kwesimba hachigone kudzoserwa panguva yekuchaja. Zvakaita se:

Lithium manganese oxide positive electrode uye solvent inokonzeresa micro-battery mhedzisiro uye kuzviburitsa, zvichikonzera kurasikirwa kwesimba kusingadzoreki:

LiyMn2O4+xLi++xe-→Liy+xMn2O4

Solvent mamorekuru (akadai sePC) anoiswa oxidized pamusoro peiyo conductive zvinhu kabhoni dema kana yazvino muunganidzi se microbattery anode:

xPC→xPC-zvakanyanya+xe-

Saizvozvo, iyo yakaipa inoshanda zvinhu inogona kudyidzana ne electrolyte kukonzeresa kuzviburitsa uye kukonzeresa kurasikirwa kwesimba, uye iyo electrolyte (senge LiPF6) inoderedzwa pane conductive zvinhu:

PF5+xe-→PF5-x

Lithium carbide iri munzvimbo yakachajwa inoiswa oxidized nekubvisa lithium ions seyakaipa electrode yemicrobattery:

LiyC6→Liy-xC6+xLi+++xe-

Factors affecting self-discharge: the manufacturing process of the positive electrode material, the manufacturing process of the battery, the properties of the electrolyte, temperature, and time.