Lub roj teeb tshuaj tiv thaiv mechanism yog dab tsi?

Lub roj teeb tshuaj tiv thaiv mechanism yog dab tsi?

Tam sim no, tsis muaj qhov tseeb thiab kev nkag siab zoo ntawm cov tshuaj tiv thaiv electrochemical ntawm LiFePO₄ hauv kev lag luam. Daim ntawv thov ntawm kev sib xyaw anion (PO₄)³⁻ ua rau hlau-raws li cov khoom siv sib xyaw zoo tshaj plaws rau lithium-ion roj teeb cathodes. Txawm li cas los xij, cov qauv siv lead ua ntawm LiFePO₄ txwv nws cov conductivity thiab lithium-ion diffusion kev ua tau zoo, ua rau txo qis hauv cov khoom siv hluav taws xob. Tsis zoo li cov ntaub ntawv txheej, tus nqi- paug nkhaus ntawm LiMPO₄ feem ntau muaj lub tiaj tiaj tiaj, uas yog tus yam ntxwv ntawm ob- theem kev tshwm sim, txhais tau hais tias ib theem kev hloov pauv ntawm LiMPO₄ thiab MPO₄ tshwm sim thaum lithium- ion intercalation / deintercalation.

LiFePO4 tau dhau los ua ob-theem tshuaj tiv thaiv kab mob thaum lub sijhawm them thiab tawm hauv lub roj teeb, piv txwv li

Reaction mechanism model

Thaum them nyiaj, Li⁺ tsiv tawm ntawm FeO₆ txheej, dhau los ntawm electrolyte, thiab nkag mus rau qhov tsis zoo electrode. Fe²⁺ yog oxidized rau Fe³⁺, thaum electrons taug kev los ntawm sab nraud Circuit Court mus rau qhov tsis zoo electrode ntawm tus neeg sawv cev tiv tauj thiab tam sim no collector. Cov txheej txheem tso tawm yog rov qab.

Los piav txog ob - theem tus cwj pwm, Padhi thiab Goodenough li al. thawj lub tswv yim "core-plhaub qauv," uas posits tias cov lithium-ion intercalation/deintercalation txheej txheem tshwm sim ntawm LiFePO₄/FePO₄ ob-theem interface, raws li qhia hauv daim duab 4-3a.

Thaum them nyiaj, LiFePO₄ / FePO₄ interface txuas ntxiv txav los ntawm qhov chaw mus rau qhov chaw, thawb mus rau qhov tseem ceeb. Li⁺ tsis tu ncua mus rau sab nraud, thiab sab nrauv LiFePO₄ tsis tu ncua hloov mus rau FePO₄. Lithium ions thiab electrons tsis tu ncua dhau los ntawm cov tshiab tsim ob -theem interface kom tswj tau qhov zoo tam sim no, tab sis lithium- ion diffusion tus nqi yog nyob rau hauv qee yam kev mob. Raws li qhov sib cuam tshuam ntawm ob theem qis, qhov sib txawv ntawm lithium ions thaum kawg yuav tsis txaus los tuav lub zog tam sim no. Lub LiFePO₄ hauv cov tub ntxhais particle yuav tsis siv tag nrho, ua rau muaj peev xwm poob. Tom qab them nyiaj tiav lawm, tsis siv LiFePO₄ yuav nyob twj ywm hauv nruab nrab ntawm cov khoom.

Xav txog tias lithium ions tuaj yeem ua rau tib lub sijhawm intercalate thiab deintercalate ntawm ntau qhov chaw, Andersson li al. thov tus qauv mosaic los piav qhia txog qhov pib poob peev, raws li pom hauv daim duab 4-3b. Cov qauv mosaic pom zoo tias txawm hais tias lithium ion intercalation thiab deintercalation txheej txheem yog nyob rau ntawm LiFePO₄/FePO₄ ob-theem interface, cov txheej txheem tuaj yeem tshwm sim ntawm txhua qhov chaw hauv cov khoom. Thaum them nyiaj, FePO₄ cheeb tsam nthuav dav ntawm cov ntsiab lus sib txawv ntawm cov khoom sib txawv, thiab cov npoo ntawm cov cheeb tsam no hla kev sib cuag, tsim ntau qhov chaw tuag tsis tuaj yeem, yog li ua rau muaj peev xwm poob. Thaum lub sij hawm tso tawm, qhov rov qab tshwm sim tshwm sim, nrog lithium ions intercalating rau FePO₄ theem. Ib feem ntawm cov tub ntxhais uas lithium ions tsis sib txuas ua rau muaj peev xwm poob.

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

Ob lub theoretical qauv tau tsim ib txhij, tab sis lub hauv paus - qauv plhaub tau txais ntau dua los ntawm cov kws tshawb fawb, txawm hais tias cov ntaub ntawv tshwj xeeb ntawm lub plhaub thiab cov tub ntxhais tseem muaj kev tsis sib haum xeeb. Raws li ob qho qauv no, nws tuaj yeem txiav txim siab tias qhov diffusion kinetics ntawm lithium ions thiab nqi yog qhov txiav txim siab rau kev siv tswv yim ntawm tag nrho cov khoom siv electrode. Hauv kev npaj cov khoom siv lithium hlau phosphate cathode, kev siv zog ua kom tau cov khoom me me thiab cov khoom me me (nanoscale lossis microporous), siv cov pa roj carbon txheej (nanocarbon zaj duab xis) thiab ion doping los txhim kho conductivity thiab lithium ion diffusion.

Nrog rau kev nkag siab tob dua ntawm LiMPO cov ntaub ntawv, nws tau pom tias ob tus qauv no tsis saib xyuas cov yam ntxwv anisotropic ntawm lithium ion thauj hauv LiMPO cov ntaub ntawv. Laffont tau tshaj tawm "Tshiab Core-plhaub Model" los kho qhov tsis txaus ntawm "core- qauv plhaub." Tsim los ntawm qhov no, Delmas tau kawm LiFePO cov khoom nyob rau hauv ntau lub xeev depletion thiab tau npaj "Domino-cascade Model," uas piav qhia tau zoo txog kev them nqi sai thiab kev tso tawm ntawm cov khoom siv nanoscale, raws li qhia hauv daim duab 4-4.

Txawm hais tias muaj qhov sib txawv tseem ceeb ntawm cov qauv uas tau hais los saum no, qhov teeb meem tseem ceeb nyob hauv qhov kev kwv yees thiab tus cwj pwm ntawm ob-theem interface. Txij li thaum lub kinetics ntawm lithium insertion / extraction thiab cov theem hloov yog nyob ntawm qhov loj me me, morphology, thiab physicochemical zog ntawm cov khoom, cov kev sib tham saum toj no (xws li kev tsis sib haum xeeb ntawm cov qauv) tej zaum yuav yog vim muaj kev sim tsis txaus.

Nrog rau kev txhim kho ntawm microscopy thiab spectroscopy, cov tshuaj daws teeb meem thiab cov theem nruab nrab tau pom thiab pom thaum lub sijhawm hloov pauv ntawm LiMPO4 cov ntaub ntawv, qhia tias lwm cov txheej txheem hloov pauv yuav muaj nyob hauv LiMPO4 cov ntaub ntawv. Hauv cov kev daws teeb meem zoo ib yam, cov cell tsis thiab ntim ntawm tes nthuav tawm kev hloov pauv tsis tu ncua thaum lub sijhawm hloov pauv. Los ntawm qee qhov kev ntsuas huab cua thiab cov txheej txheem ua tus cwj pwm, xws li ultra- cov khoom me me (nanoscale) thiab siab - tus nqi them - tso tawm (siab dua 10C), cov tshuaj tiv thaiv zoo thiab qhov muaj nyob ntawm cov theem nruab nrab tau pom hauv LiMPO4.

Kev hloov pauv theem thaum them nqi- cov txheej txheem tawm ntawm chav tsev kub. Cov roj teeb lithium-ion muaj qhov zoo thim rov qab thaum them nqi- tawm mus, uas cuam tshuam nrog cov qauv zoo sib xws ntawm cov theem tom qab lithium-ion deintercalation/intercalation. Thaum lub sij hawm them nqi- cov txheej txheem tso tawm, lub peev xwm lwj ntawm lub roj teeb muaj feem cuam tshuam nrog rau theem hloov kinetics. Raws li cov qauv ntawm LiFePO4, [100]pmnb kev taw qhia yog qhov zoo tshaj plaws rau lithium{10}}ion tsiv teb tsaws, thiab qhov sib cuam tshuam ntawm ob theem txav raws c-axis thaum them nqi{12}} cov txheej txheem tawm.

(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, lub ncov diffraction ntawm Li₁₋δFePO₄ pib ploj mus, thiab qhov kev siv ntawm lub ncov diffraction uas tsim los ntawm FePO₄ maj mam nce. Conversely, raws li lithium ions raug tso, qhov kev siv ntawm lub diffraction ncov tsim los ntawm FePO₄ maj mam txo, thiab qhov kev siv ntawm lub diffraction ncov tsim los ntawm Li₁₋δFePO₄ maj mam nce.

(2) LiₓFePO₄/Li₁₋yFePO₄LiₓFePO₄ ntawm chav tsev kub yog qhov sib xyaw ntawm Fe³⁺/Fe²⁺ sib xyaw-valence mesophase LiₐFePO₄/Li₁₋ FePO₄. thiab sawv cev rau cov cab kuj ceev thiab hopping probability thaum them thiab tso tawm, feem. Powder neutron diffraction qhia tau hais tias qhov zoo tshaj qhov tseem ceeb rau thiab yog 0.05 thiab 0.11, feem. Yam xws li ion doping, kub, hloov pauv hlau, particle loj, thiab tsis yog-equilibrium xeev ntawm overpotential tag nrho cuam tshuam cov nqi ntawm thiab . Ua kom muaj txiaj ntsig ntawm thiab yuav txhim kho cov kev ua haujlwm kinetic ntawm cov tshuaj tiv thaiv electrode thaum lub sij hawm them thiab tawm ntawm chav tsev kub.

Ntawm 450 degree, muaj kev daws teeb meem ntawm LiₓFePO₄, thaum nyob hauv chav tsev kub, muaj ob theem metastable: Li₀.₇₅FePO₄ thiab Li₀.₅FePO₄. Tshaj 500℃, LiₓFePO₄ pib decompose rau hauv cov tsis yog -olivine compounds; cov muaj pes tsawg leeg thiab cov ntsiab lus ntawm cov phosphates los yog phosphides nyob ntawm tus nqi ntawm x. Nyob nruab nrab ntawm 400 thiab 500 degree, tsuas yog ib qho kev daws teeb meem ntawm LiₓFePO₄ muaj.

Cov kev hloov thaum lub sij hawm txias yog ntau nyuaj tshaj li thaum lub sij hawm cua sov. Qhov sib xyaw ntawm qhov sib tov thaum lub caij txias yog nyob ntawm tus nqi ntawm x thiab cov txheej txheem thermal. Thaum txias, LiₓFePO₄ thawj zaug decomposes rau hauv ib qho kev sib xyaw ntawm ob theem tsis yog-olivine, qhov feem ntawm qhov yog nyob ntawm tus nqi pib ntawm qhov kub thiab txias. Thaum qhov kub thiab txias qis dua (140 ± 20 degree), ob lub-theem txheej txheem dhau los ua cov txheej txheem nyuaj, nyob rau hauv uas LiFePO₄ thiab FePO₄ coexist nrog ob lwm olivine- hom compounds, Liₓ₁FePO₄ thiab Liₓ₂FePO₄. Kev laus qhov sib tov ntawm chav tsev kub ua rau plaub-theem system maj mam hloov mus rau ob-theem system ntawm LiFePO₄ thiab FePO₄.

Battery reaction mechanism

FePO₄ muaj nyob rau hauv ntau lub tsev: ① Tom qab ua tiav delithiation ntawm LiFePO₄, orthorhombic FePO₄ yog tsim; ② Triclinic FePO₄ muaj quartz-zoo li cov qauv, nrog rau tag nrho cov cations tetrahedral ua haujlwm; ③ Monoclinic thiab orthorhombic FePO₄ tuaj yeem npaj los ntawm lawv cov hydrates. Tag nrho cov ntaub ntawv crystalline ntawm FePO₄, nrog rau amorphous FePO₄, tuaj yeem hloov mus rau hauv triclinic FePO₄ thaum cua sov.

Kev hloov pauv ntawm LiFePO₄ mus rau FePO₄ qeeb thiab tsis tiav, tab sis ua tiav thaum qhov kub siab tshaj 500 degree. Nyob rau hauv lub roj teeb kev khiav hauj lwm tej yam kev mob, cov khoom cathode yog kinetically ruaj khov. Thaum lub sij hawm synthesis ntawm LiFePO₄, nws yog ib qho tseem ceeb kom ntseeg tau tias tsis muaj FePO₄. Yog tias tam sim no, triclinic FePO₄ yuav raug tsim los ntawm cua sov, ua rau tsis muaj -electrochemically active glassy theem ntawm cov khoom nto ntawm qhov kub thiab txias.

Ion doping tuaj yeem txhim kho cov conductivity ntawm cov ntaub ntawv. P- hom semiconductor conductive cov ntaub ntawv nrog conductivity ncav cuag 10⁻² S / cm yog tau los ntawm ion doping. Doping is a very complex process: on the one hand, density functional theory (DFT) calculations of the electronic structure of LiFePO₄ under the local density approximation (LDA) and generalized gradient approximation (GGA) show that the material should exhibit characteristics of a metallic or semiconductor material, with a conduction band and valence band width of approximately 0.3 eV, which is inconsistent nrog qhov tsawg conductivity ua tau kuaj pom. Ntawm qhov tod tes, xav txog kev sib cuam tshuam ntawm electron orbitals thiab Coulomb kev sib cuam tshuam tom qab ion doping, kev txhim kho valence band qauv yog theoretically ua tau.

DFT xam ntawm Mg- lossis Cr-doped LiFePO₄ qhia tias qhov siab tshaj plaws ntawm cov hluav taws xob hluav taws xob nyob ze ntawm qib Fermi, uas piav qhia txog cov khoom siv hlau ntawm cov khoom siv doped. Kev hloov pauv hauv conductivity tshwm sim los ntawm ion doping tuaj yeem cuam tshuam nrog cov hauv qab no:

1) Cov npoo ntawm cov khoom thauj khoom thauj khoom yog metallized.

2) Ion doping nqaim qhov dav ntawm valence band thiab conduction band.

3) Tshaj ib qho tseem ceeb heev concentration, lub electron wavefunction ntawm dopant ions ua rau tsim ib tug conduction band.

4) Hom, concentration, thiab kev faib tawm ntawm dopant ions.

5) Nyob rau hauv ntau M-O hlau oxides, ib tug hlau conduction band tshwm thaum lub M-M daim ntawv cog lus deb tsawg dua 3 × 10⁻¹⁰ m.

6) Thaum lub sij hawm synthesis, qhov sib ntxiv ntawm cov pa roj carbon monoxide ua rau cov pa roj carbon txheej ntawm cov khoom, tsim kom muaj txoj hauv kev zoo.

7) Cov tsos ntawm Fe₂P. Thaum lub sij hawm synthesis, qhov sib ntxiv ntawm cov pa roj carbon ntau txo cov phosphate.

Ion doping and conductivity

8) Lub Fe³⁺ / Fe²⁺ redox khub ua raws li cov khoom siv hauv kev txo qis LiFePO₄.

LiFePO₄ nthuav tawm kev ua haujlwm nrog cov khoom siv electrolytes. Electrochemical tus cwj pwm ntawm cov khoom yog heev correlated nrog nws nto chemistry nyob rau hauv lub electrolyte. Feem ntau, ib zaj duab xis passivation rau ntawm cov khoom nto. Cov yeeb yaj kiab no txhawb nqa lithium-ion diffusion, tiv thaiv kev poob ntawm cov khoom nquag, thiab yuav tsum tiv taus qhov ntim thiab qhov chaw hloov pauv thaum lub sij hawm lithium-ion insertion/extraction. Cov pa roj carbon-coated LiFePO₄ cov zaj duab xis saum npoo muaj cov khoom sib xyaw xws li LiF, LiPF₆, LiₓFᵧ⁻, thiab LiₓPOᵧFᶻ⁻.

Cov electrolytes feem ntau muaj alkyl carbonates thiab lithium ntsev. Cov khoom siv cathode tau dhau los ua ntau qhov tshwm sim hauv cov electrolyte. Piv txwv li, hauv LiPF₆ cov kev daws teeb meem, cov kua qaub- cov tshuaj tiv thaiv hauv qab ntawm LiFePO₄ thiab cov lej ntawm HF yog qhov tsis tuaj yeem zam tau. Lub xub ntiag ntawm HF nyob rau hauv cov electrolyte muaj ob qho kev puas tsuaj: ua ntej, hloov cov tshuaj tiv thaiv ntawm hlau ions thiab protons; thiab qhov thib ob, cov tshuaj tiv thaiv ntawm Li ions thiab F ions ntawm qhov chaw me me los ua LiF, uas cuam tshuam Li⁺ diffusion.

Iron ions yaj hauv electrolytes. Kev ntsuam xyuas ntawm cov hlau ion yaj ntawm LiFePO₄ hauv cov electrolytes sib txawv tau qhia cov hauv qab no:

1) Nyob rau hauv electrolytes tsis muaj acidic contaminants, txawm nyob rau hauv siab kub, lub dissolution ntawm hlau ions thiab ua rau poob loj ntawm cov active khoom yog negligible.

2) Cov kua qaub ntau dua ua rau cov hlau ion yooj yim dua.

3) Kev kub siab ua rau cov hlau ion tawg yooj yim dua.

4) Cov ntsiab lus carbon ntau dua hauv cov khoom ua rau cov khoom ruaj khov dua.

Qhov chaw sib cuag ntawm cov khoom siv thiab cov ntaub ntawv yog feem ntau raug rau corrosion. Qhov kev tiv thaiv corrosion no tuaj yeem zam tau los ntawm kev siv alkaline mesophase los yog siv cov kua qaub scavening additives. Hauv lithium- roj teeb ion siv LiFePO₄ ua cov khoom siv cathode, tsis yog-acidic electrolytes lossis carbon ntxiv lossis txheej ntawm LiFePO₄ tuaj yeem siv los tiv thaiv kev poob.

Cov yam ntxwv kinetic ntawm LiFePO₄ cov ntaub ntawv cathode tseem tsis tau nkag siab tag nrho. Nws feem ntau ntseeg tias qhov loj me thiab kev faib tawm, kev coj ua, ion diffusion, kinetics thaum lub sij hawm hloov pauv (them- txheej txheem tawm), thiab carbon txheej / doping tag nrho cuam tshuam rau lub roj teeb kev ua tau zoo ntawm tus nqi sib txawv - paug tus nqi. Uniform carbon doping txhais tau hais tias lithium ions thiab electrons tuaj yeem tso thiab muab rho tawm ntawm tib qhov chaw hauv cov khoom siv, txo cov electrode polarization.

(1) Kev cuam tshuam ntawm kev coj tus kheej ntawm Kev Muaj Peev Xwm Tsis tshua muaj hluav taws xob ntawm LiFePO₄ ncaj qha ua rau txo qis hauv siab - tus nqi tso tawm lub peev xwm ntawm lub roj teeb. Lub conductivity ntawm ntshiab LiFePO₄ yog kwv yees li 10⁻⁹ S / cm, thiab lub peev xwm paug poob sharply los ntawm 148 mA·h / g ntawm 0.2C paug tus nqi mus rau 85 mA·h / g ntawm 5C paug tus nqi. Lub siab - tus nqi tso tawm peev ntawm cov khoom siv cathode tsis tas li nce nrog nce conductivity. Thaum tsis tshua muaj conductivity, qhov nce hauv conductivity txhim kho electrochemical kinetics ntawm cov khoom. Thaum cov khoom siv conductivity tshaj ib qho tseem ceeb, conductivity tsis yog qhov tseem ceeb rau cov khoom tus nqi peev xwm. LiFe₀.₉Ni₀.₁PO₄ (1.0 × 10⁻⁷ S / cm), nrog rau nws cov conductivity tsawg, nthuav tawm zoo siab - tus nqi tso tawm ntau dua li LiFePO₄ (4.0 × 10⁻⁶ S / cm), nrog paug tawm peev xwm ntawm 5·g / 9 mh Feem ntau, ntawm 10C tawm tus nqi. Qhov no qhia tau tias lithium{24}}ion diffusion yuav tau hloov cov conductivity raws li qhov kev txiav txim siab nyob rau hauv lub electrochemical zog ntawm lithium{25}} ion roj teeb.

(2) Lithium-ion Diffusion Lithium{2}}ion diffusion yog txiav txim los ntawm ob qho tib si sab hauv thiab sab nraud. Sab nraud yam muaj xws li particle loj, faib, thiab morphology. Cov yam ntxwv sab hauv feem ntau yog xa mus rau lithium-ion diffusion coefficient. Lub lithium-ion diffusion coefficient yog tus nqi tas li; Lub peev xwm diffusion ntawm lithium ions txo qis nrog nce particle loj vim hais tias txoj kev diffusion ntawm lithium ions nyob rau hauv cov particle nce. Lub peev xwm diffusion ntawm lithium ions yog inversely proportional rau lub square ntawm particle loj thiab ncaj proportional rau lithium -ion diffusion coefficient. Qhov loj me me muaj qhov cuam tshuam ntau dua rau lithium{11}}ion diffusion dua li diffusion coefficient. Kev suav lej ntawm lithium{13}}ion diffusion coefficient yuav tsum tau ua ke nrog cov kev ntsuas tshwj xeeb thiab cov qauv theoretical. Cov kev ntsuas tseem ceeb yog galvanostatic titration (GITT) thiab electrochemical impedance spectroscopy (EIS lossis AC Impedance).

(3) Ob-dimensional scale electrodes: Nyias-film electrodes txhim kho electrode kev ua si los ntawm qhov chaw saum npoo. Nyob rau hauv nyias- zaj duab xis electrodes, electrons nkag mus rau tam sim no collector thaum lithium ions nkag mus rau electrolyte los ntawm qhov opposite direction. Nrog rau kev tsim ntawm FePO₄ txheej, kev tiv thaiv rau electron zog txo, thaum lub zog tiv thaiv lithium-ion zog nce. FePO₄ thawj nucleates ntawm crystal defects thiab tom qab ntawd loj hlob nyob rau hauv tag nrho cov kev taw qhia, inhibiting lithium-ion diffusion mus txog rau thaum lithium ions tsis tuaj yeem khiav ntawm [100] kev taw qhia.