Chii chinonzi Battery reaction mechanism?

Chii chinonzi Battery reaction mechanism?

Parizvino, hapana kwakaringana uye kunoenderana nekunzwisisa kwe electrochemical reaction mechanism yeLiFePO₄ muindasitiri. Kushandiswa kwecomposite anion (PO₄)³⁻ kunoita kuti iron-igadziriswe makombonis emhando yelithium-ion battery cathodes. Zvakadaro, chimiro chekristaro cheLiFePO₄ chinodzikamisa conductivity yayo uye lithium-ion diffusion performance, zvichikonzera kudzikira kwekuita kwemagetsi emagetsi. Kusiyana nemidziyo yakaturikidzana, kuchaja-kubuditsa kweLiMPO₄ kunowanzoita nzvimbo yakati sandara, inova chimiro chezvikamu zviviri-zvinoitika, zvichireva kuti chikamu chekuchinja pakati peLiMPO₄ neMPO₄ chinoitika panguva yelithium{8}}ion intercalation/deintercalation.

LiFePO4 inoitwa maviri-phase reaction mechanism panguva yekuchaja uye kubuda mubhatiri, kureva.

Reaction mechanism model

Panguva yekuchaja, Li⁺ inotama kubva kuFeO₆ layer, inopfuura nepakati pe electrolyte, uye inopinda mune iyo yakaipa electrode. Fe²⁺ inoiswa oxidized kuenda kuFe³⁺, ukuwo maerekitironi achifamba kubva kudunhu rekunze kuenda kune negative electrode kuburikidza neanobata conductive agent uye muunganidzi aripo. The discharge process is the reverse.

Kutsanangura maitiro ezvikamu zviviri izvi, Padhi naGoodenough et al. akatanga aronga "core-shell model," iyo inoratidza kuti lithium-ion intercalation/deintercalation process inoitika paLiFePO₄/FePO₄ two-phase interface, sezvaratidzwa mumufananidzo 4-3a.

Panguva yekuchaja, iyo LiFePO₄/FePO₄ interface inoramba ichifamba kubva pamusoro ichienda pakati, ichisundira yakananga kupakati. Li⁺ inoramba ichifamba ichienda kunze, uye yekunze LiFePO₄ inoramba ichichinja kuita FePO₄. Lithium ions nema electrons anoramba achipfuura nepakati pezvichangobva kuumbwa zviviri-pase interface kuti irambe ichishanda, asi lithium-ion diffusion rate inongoramba iripo mune mamwe mamiriro. Sezvo kuwirirana pakati pezvikamu zviviri izvi kunoderera, kupararira kwe lithium ions kunozopedzisira kusina kukwana kuchengetedza ikozvino inoshanda. Iyo LiFePO₄ muchikamu chepakati haizoshandiswe zvizere, zvichikonzera kurasikirwa kwehukuru. Mushure mekuchaja kwapera, LiFePO₄ isina kushandiswa icharamba iri pakati pechikamu.

Tichifunga kuti lithium ions inogona panguva imwe chete kupindirana uye kupindirana munzvimbo dzakawanda, Andersson et al. akakurudzira mufananidzo wemosaic kuti utsanangure kurasikirwa kwesimba kwekutanga, sezvakaratidzwa mumufananidzo 4-3b. Iyo mosaic modhi inotsigira kuti kunyangwe iyo lithium ion intercalation uye deintercalation process iri paLiFePO₄/FePO₄ maviri-phase interface, maitiro anogona kuitika chero nzvimbo mukati mechikamu. Panguva yekuchaja, dunhu reFePO₄ rinowedzera panzvimbo dzakasiyana pachikamu, uye mipendero yenzvimbo idzi inoyambuka, ichigadzira nzvimbo zhinji dzakafa dzisingaite, nekudaro zvichikonzera kurasikirwa kwehunyanzvi. Panguva yekuburitsa, reverse reaction inoitika, ne lithium ions inopindirana muchikamu cheFePO₄. Chikamu chiri pamusimboti apo lithium ions isina kupindirana inoguma mukurasikirwa kwehukuru.

Figure 4-3 Lithium-ion intercalation/deintercalation model of lithium iron phosphate battery

Mamodheru maviri edzidziso akagadzirwa panguva imwe chete, asi musimboti-muenzanisi wegoko unogamuchirwa zvakanyanya nevatsvakurudzi, kunyange zvazvo zvinhu zvegoko nepakati zvichiramba zvichinetsa. Zvichienderana nemhando mbiri idzi, zvinogona kugumiswa kuti diffusion kinetics ye lithium ions uye kubhadharisa ndizvo zvinogadzirisa zvekushandisa kunoshanda kwese electrode zvinhu. Mukugadzirira kwe lithium iron phosphate cathode zvinhu, kuedza kunoitwa kuwana zvidimbu zvine diki uye yunifomu particle size (nanoscale kana microporous), uchishandisa kabhoni coating (nanocarbon firimu) uye ion doping kuvandudza conductivity uye lithium ion diffusion.

Nekunzwisisa kwakadzama kwezvinhu zveLiMPO, zvakaonekwa kuti mhando mbiri idzi dzakaregeredza maitiro anisotropic ekutakura kwelithium ion muLiMPO zvinhu. Laffont akaronga "New Core-shell Model" kugadzirisa kukanganisa kwe"core-shell model." Achivakira pane izvi, Delmas akadzidza LiFePO zvimedu munzvimbo dzakasiyana dzekupera uye akaronga "Domino-cascade Model," inotsanangura zvinobudirira kumhanyisa kuchaja uye kuburitsa kuita kwenanoscale particles, sezvakaratidzwa muFigure 4-4.

Zvisinei nekusiyana kwakakura pakati pemamodheru ambotaurwa, nyaya huru iri mukufembera uye maratidziro ezvikamu zviviri-zvinoratidzwa. Sezvo kinetics ye lithium kuisa / kubviswa uye kushanduka kwechikamu kunonyanya kuenderana nehukuru hwechidimbu, morphology, uye physicochemical zvinhu zvemashoko, hurukuro dziri pamusoro (kusanganisira kukakavara pakati pemienzaniso) inogona kunge yakakonzerwa nemamiriro asina kukwana ekuedza.

Nekuvandudzwa kwemicroscopy uye spectroscopy, mhinduro yakasimba yemhinduro uye zvikamu zvepakati zvakaonekwa uye zvakaonekwa panguva yekuchinja kwechikamu cheLiMPO4 zvinhu, zvichiratidza kuti imwe nzira yekushandura chikamu inogona kuvapo muLiMPO4 zvinhu. Mune yakajairwa yakasimba mhinduro maitiro, maseru paramita uye sero vhoriyamu inoratidza inoenderera shanduko panguva yekuchinja kwechikamu. Kuburikidza nemamwe mamiriro ekuyedza akanyanya uye nzira dzehunhu, dzakadai seyekupedzisira-diki diki (nanoscale) uye yakakwirira-reti yekuchaja-kuburitsa (pamusoro pe10C), mhinduro yakasimba uye kuvapo kwezvikamu zvepakati zvakaonekwa muLiMPO4.

Phase transitions panguva yekuchaja-maitiro ekuburitsa patembiricha yemumba. Lithium-mabhatiri eion anoratidza kuchinjika kwakanaka panguva yekuchaja-kutenderera kwechaji, izvo zvinoenderana nekufanana kwechimiro pakati pechikamu chenyika mushure melithium-ion deintercalation/intercalation. Panguva yekuchaja-kuburitsa, kuwora kwebhatiri kunoenderana zvakanyanya nechikamu chekuchinja kinetics. Zvinoenderana nechimiro cheLiFePO4, iyo [100]pmnb direction inonyanyonakira parithium-ion migration, uye chinongedzo chiri pakati pezvikamu zviviri chinofamba ne c{11}}axis panguva yekuchaja{12}}maitiro ekuburitsa.

(1) LiFePO₄/FePO₄The ratio of LiFePO₄/FePO₄ changes continuously with the battery charge-discharge reaction (the value of x in LiₓFePO₄ changes continuously). As lithium ions are extracted, the intensity of the diffraction peak produced by LiFePO₄ gradually decreases. When δ>0.2, iyo diffraction peak yeLi₁₋δFePO₄ inotanga kunyangarika, uye kusimba kweiyo diffraction peak inogadzirwa neFePO₄ zvishoma nezvishoma inowedzera. Sezvineiwo, sezvo lithium ions inoiswa, kusimba kweiyo diffraction peak inogadzirwa neFePO₄ inoderera zvishoma nezvishoma, uye kusimba kweiyo diffraction peak inogadzirwa naLi₁₋δFePO₄ zvishoma nezvishoma inowedzera.

(2) LiₓFePO₄/Li₁₋yFePO₄LiₓFePO₄ patembiricha yemumba musanganiswa weFe³⁺/Fe²⁺ musanganiswa-valence mesophase LiₐFePO₄/Li₁₋ FePO₄. uye inomiririra density yekutakura uye kusvetuka mukana panguva yekuchaja nekuburitsa, zvichiteerana. Powder neutron diffraction yakaratidza kuti iwo akanyanya kukosha uye ari 0.05 uye 0.11, zvichiteerana. Zvinhu zvakadai seion doping, tembiricha, shanduko yesimbi, particle size, uye zvisiri{6}}equilibrium states panguva yakawandisa zvinokanganisa hunhu hwe uye . Kuwedzera kukosha uye kuchavandudza mashandiro ekinetic eiyo electrode reaction panguva yekuchaja uye kuburitsa pane tembiricha.

Pa 450 dhigirii, mhinduro yakasimba yeLiₓFePO₄ iripo, nepo pakamuri tembiricha, maviri metastable zvikamu zviripo: Li₀.₇₅FePO₄ uye Li₀.₅FePO₄. Pamusoro pe500 degree, LiₓFePO₄ inotanga kuora kuita isiri-olivine compounds; kuumbwa uye zvirimo zveizvi phosphates kana phosphides zvinoenderana nekukosha kwe x. Pakati pe400 ne500 degree, chete mhinduro yakasimba yeLiₓFePO₄ iripo.

Iko kushanduka panguva yekutonhora kwakanyanya kuoma kupfuura iyo panguva yekupisa. Kuumbwa kwemusanganiswa panguva yekutonhora kunoenderana nekukosha kwe x uye nzira yekupisa. Pakutonhodza, LiₓFePO₄ inotanga kuwora kuita musanganiswa wezvikamu zviviri zvisiri-maolivine, uwandu hwacho hunoenderana nehukoshi hwekutanga hwetembiricha uye x. Kana tembiricha iri pasi (140±20 degree), maviri-phase system anova system yakaoma, umo LiFePO₄ neFePO₄ zvinogarisana nemamwe maviri emhando ye olivine{7}}compounds, Liₓ₁FePO₄ neLiₓ₂FePO₄. Kuchembera musanganiswa uyu patembiricha yemumba kunoita kuti ina-phase system ishanduke zvishoma nezvishoma kuita{10}}phase system yeLiFePO₄ neFePO₄.

Battery reaction mechanism

FePO₄ iripo muzvimiro zvakati wandei: ① Mushure mekupedzwa kwakazara kweLiFePO₄, orthorhombic FePO₄ inoumbwa; ② Triclinic FePO₄ ine quartz-yakafanana chimiro, ine cations ese tetrahedral coordinated; ③ Monoclinic uye orthorhombic FePO₄ inogona kugadzirirwa kubva kumahydrates avo. Ese aya macrystalline mafomu eFePO₄, pamwe neamorphous FePO₄, anogona kushandurwa kuita triclinic FePO₄ pakudziya.

Shanduko kubva kuLiFePO₄ kuenda kuFePO₄ inononoka uye haina kukwana, asi inokwana kana tembiricha yadarika 500℃. Pasi pemamiriro ekushanda kwebhatiri, iyo cathode zvinhu inogadzikana kinetically. Munguva yekuumbwa kweLiFePO₄, zvakakosha kuve nechokwadi kusavapo kweFePO₄. Kana iripo, triclinic FePO₄ ichagadzirwa pakudziya, zvichiita kuti pave ne-electrochemically active glassy phase panzvimbo inodziya zvikuru.

Ion doping inogona kuvandudza conductivity yezvinhu. P-type semiconductor conductive materials ine conductivity inosvika 10⁻² S/cm inowanikwa kuburikidza neion doping. Doping inzira yakaoma kwazvo: kune rumwe rutivi, density functional theory (DFT) maverengero emagetsi chimiro cheLiFePO₄ pasi penzvimbo density approximation (LDA) uye generalized gradient approximation (GGA) inoratidza kuti zvinhu zvacho zvinofanirwa kuratidza hunhu hwesimbi kana semiconductor zvinhu, ine conduction band uye valence ine yakaderera bhendi yeVV ine hupamhi hwakaderera. kunyatsoonekwa. Kune rimwe divi, tichifunga nezvekudyidzana kwemaelectron orbitals uye Coulomb kudyidzana mushure meion doping, yakagadziridzwa valence bhendi chimiro chinogoneka.

DFT macalculations eMg- or Cr-doped LiFePO₄ anoratidza kuti kuremesa density yeelectronic states iri pedyo neFermi level, iyo inotsanangura mabatirwo esimbi ezvakagadzirwa. Shanduko mukufambiswa kunokonzerwa neion doping inogona kunge yakabatana nezvinhu zvinotevera:

1) Mipendero yematunhu anotakura anotakura ane simbi.

2) Ion doping inoderedza hupamhi hwebhendi yevalence uye conduction bhendi.

3) Kupfuura kumwe kuomesesa, iyo electron wavefunction yeiyo dopant ion inotungamira mukuumbwa kwebhendi rekufambisa.

4) Rudzi, kutarisisa, uye kugovera dopant ion.

5) Mune akawanda M-O maokisijeni esimbi, bhendi resimbi rinoonekwa kana M-M chinhambwe chebhondi chiri pasi pe3 × 10⁻¹⁰ m.

6) Panguva yekubatanidza, kuwedzera kweiyo organic kabhoni kunokonzera kabhoni kupfekedzwa kwezvinhu, kugadzira inobudirira conduction nzira.

7) Kuonekwa kweFe₂P. Panguva yekubatanidza, kuwedzera kwekabhoni yakawandisa kunoderedza phosphate.

Ion doping and conductivity

8) Iyo Fe³⁺/Fe²⁺ redox pair inoita seinokonzeresa mukudzikiswa kweLiFePO₄.

LiFePO₄ inoratidza reactivity ine anowanzo shandiswa electrolytes. Maitiro emagetsi echinyorwa anoenderana zvakanyanya neayo epamusoro chemistry mukati me electrolyte. Kazhinji, firimu rekufambisa rinoumbwa pamusoro pezvinhu. Firimu iri rinoita kuti lithium-ion diffusion, ridzivirire kurasikirwa kwezvinhu zvinoshanda, uye rinofanirwa kushingirira kushanduka kwevhoriyamu nepamusoro panguva yelithium-inoiswa/kubviswa. Carbon-yakavharidzirwa LiFePO₄ mafirimu epamusoro ane zvinhu zvakaita seLiF, LiPF₆, LiₓFᵧ⁻, uye LiₓPOᵧFᶻ⁻.

Maelectrolyte akajairika anowanzo ane alkyl carbonates uye lithium munyu. Iyo cathode zvinhu inosangana nezvakawanda zvinogona kuitika mu electrolyte. Semuyenzaniso, muLiPF₆ mhinduro, iyo asidhi-base reaction pakati peLiFePO₄ nekutsvaga huwandu hweHF haidzivisiki. Kuvapo kweHF mu electrolyte kune zvinhu zviviri zvinokuvadza: kutanga, kushandiswa kwekutsiva pakati peiyoni yesimbi nemaproton; uye chechipiri, kuita kweLi ions neF ions pane chidimbu chepamusoro kuumba LiF, iyo inotadzisa Li⁺ kupararira.

Iron ions inonyungudika mu electrolytes. Miedzo paiyo iron ion dissolution yeLiFePO₄ muma electrolyte akasiyana yakaratidza zvinotevera:

1) Muma electrolytes asina zvinosvibisa asidhi, kunyangwe patembiricha yakakwira, kunyungudika kweioni dzesimbi uye kurasikirwa kwehuwandu hwezvinhu zvinoshanda hazvina basa.

2) Yepamusoro mhinduro acidity inotungamira kune nyore kunyungudika iron ion.

3) Kupisa kwepamusoro kunotungamira kune nyore kunyungudika iron ion.

4) Yakakwira kabhoni yemukati mukati mezvinhu zvinoguma nekugadzikana kwezvinhu.

Nzvimbo yekubatana pakati pezvinhu zvinoshanda uye binder inonyanya kubatwa nekuora. Kuora uku kunogona kudzivirirwa nekushandisa alkaline mesophase kana kushandisa acidic scavenging additives. Mumabhatiri e lithium-eion anoshandisa LiFePO₄ sema cathode material, asiri-acidic electrolytes kana carbon added kana coating yeLiFePO₄ anogona kushandiswa kudzivirira kurasikirwa kukuru.

Iyo kinetic maitiro eLiFePO₄ cathode zvinhu hazvisati zvanyatsonzwisiswa. Zvinotendwa kuti saizi yechidimbu uye kugoverwa, conductivity, diffusion yeion, kinetics panguva yekuchinja kwechikamu (charge-discharge process), uye carbon coating/doping zvese zvinokanganisa kushanda kwebhatiri pachaji yakasiyana-kubuda. Uniform kabhoni doping zvinoreva kuti lithium ion uye maerekitironi anogona kuiswa uye kutorwa panzvimbo imwe chete mune inoshanda zvinhu, kuderedza electrode polarization.

(1) Pesvedzero yeKubata paKugona Kudzikira kweLiFePO₄ kunotungamirira kukudzikira kwepamusoro-mwero wekuburitsa simba rebhatiri. Iko conductivity yeLiFePO₄ yakachena inenge 10⁻⁹ S/cm, uye simba rekubuda rinodonha zvakanyanya kubva pa148 mA·h/g pa 0.2C discharge rate kusvika 85 mA·h/g pa 5C discharge rate. Iyo yakakwira{{9}reti yekuburitsa simba reiyo cathode zvinhu haiwanzo kuwedzera nekuwedzera conductivity. Pane yakaderera conductivity, kuwedzera conductivity kunovandudza electrochemical kinetics yezvinhu. Kana iyo conductivity yechinhu ichipfuura imwe yakakosha kukosha, conductivity haisisiri iyo inotaridza yehuwandu hwehuwandu hwehuwandu. LiFe₀.₉Ni₀.₁PO₄ (1.0 × 10⁻⁷ S/cm), nekudzika kwayo, ichiratidza zviri nani zvakakwirira-redhiyo yekuburitsa simba pane LiFePO₄ (4.0 × 10⁻⁶ S/cm), iine discharge 0 m/5·, 9 A/cm uye 5 mh, 9 mh. zvichiteerana, pa10C yekuburitsa mwero. Izvi zvinoratidza kuti lithium-ion diffusion ingangove yakatsiva conductivity sechinhu chakasimba muzvinhu zve electrochemical yemabhatiri e lithium-.

(2) Lithium-ion Diffusion Lithium-kupararira kweion kunotariswa nezvose zviri mukati nekunze. Zvinhu zvekunze zvinosanganisira particle size, kugovera, uye morphology. Zvinhu zvemukati zvinonyanya kureva lithium-ion diffusion coefficient. Lithium-ion diffusion coefficient inokosha inogara iripo; kugona kwekupararira kwelithium ion kunodzikira nekuwedzera particle size nekuti nzira yekupararira yelithium ions mukati mechikamu inowedzera. Kugona kupararira kwelithium ion kunopesana neskweya yehukuru hwechikamu uye zvakanangana nerithium-ion diffusion coefficient. Saizi yezvikamu zvine simba guru parithium-ion diffusion pane diffusion coefficient. Kuverengera kwenhamba yelithium-ion diffusion coefficient inofanira kusanganiswa nedzimwe nzira dzekuyera nemamodheru edzidziso. Nzira huru dzekuyera galvanostatic titration (GITT) uye electrochemical impedance spectroscopy (EIS kana AC Impedance).

3 Mumaelectrodes emufirimu matete-, maerekitironi anopinda muunganidzi iripo ukuwo maioni e lithium achipinda mu electrolyte kubva kune rimwe divi. Nekuumbwa kweFePO₄ layer, kushorwa kwe electron kufamba kunoderera, nepo kushorwa kwe lithium-ion movement inowedzera. FePO₄ inotanga nucleates pacrystal defects yozokura kumativi ose, ichidzivisa lithium-ion diffusion kusvikira lithium ions isingagoni kupukunyuka munzira [100].