Dɛn Ne Battery reaction mechanism?

Dɛn Ne Battery reaction mechanism?

Mprempren, ntease biara nni hɔ a edi mu na ɛkɔ so daa wɔ electrochemical reaction mechanism a LiFePO4 fa so yɛ adwuma no ho wɔ adwumayɛ mu. Anion a wɔabom (PO4)3− a wɔde di dwuma no ma dade-a wɔde yɛ nneɛma a wɔde yɛ nneɛma a ɛyɛ papa a wɔde di dwuma ma lithium-ion battery cathodes. Nanso, LiFePO4 ahwehwɛ nhyehyɛe no to ne conductivity ne lithium-ion diffusion adwumayɛ ano hye, na ɛma ade no electrochemical adwumayɛ so tew. Nea ɛnte sɛ nneɛma a wɔayɛ no layered no, charge-discharge curve a ɛwɔ LiMPO4 no taa nya plateau a ɛyɛ tratraa yiye, a ɛyɛ su titiriw a ɛwɔ abien-phase reactions mu, a ɛkyerɛ sɛ phase nsakrae nhyehyɛe a ɛda LiMPO4 ne MPO4 ntam no ba bere a lithium-ion intercalation/deintercalation.

LiFePO4 fa two-phase reaction mechanism mu bere a ɛrebɔ na ɛregyae batere mu, i.e.

Reaction mechanism model

Bere a wɔrebɔ charge no, Li+ tu fi FeO3 layer no mu, fa electrolyte no mu, na ɛkɔ electrode a enye no mu. Fe2+ yɛ oxidized kɔ Fe32, bere a electron ahorow no fi abɔnten circuit no mu kɔ negative electrode no mu denam contacting conductive agent ne current collector no so. Adeyɛ a wɔde yi nsu gu no yɛ nea ɛne no bɔ abira.

Sɛ yɛbɛkyerɛkyerɛ saa suban abien-fase yi mu a, Padhi ne Goodenough ne afoforo. dii kan de "core-shell model," a ɛkyerɛ sɛ lithium-ion intercalation/deintercalation nhyehyɛe no ba wɔ LiFePO4/FePO4 abien-fase ntamgyinafo no so, sɛnea wɔakyerɛ wɔ Mfonini 4-3a mu no.

Bere a wɔrebɔ charge no, LiFePO4/FePO4 interface no kɔ so fi soro kɔ mfinimfini, na ɛpia kɔ core no mu. Li+ kɔ so tu kɔ abɔnten, na akyi LiFePO4 no kɔ so dan FePO4. Lithium ions ne electrons kɔ so fa two-phase interface a wɔayɛ no foforo no mu de kura current a etu mpɔn mu, nanso lithium-ion diffusion rate no yɛ nea ɛkɔ so daa wɔ tebea horow bi mu. Bere a nkitahodi a ɛda afã abien no ntam no so tew no, awiei koraa no, lithium ions a ɛtrɛw no rennɔɔso sɛ ɛbɛkɔ so akura nsu a etu mpɔn mu. Wɔremfa LiFePO4 a ɛwɔ particle core no mu no nni dwuma koraa, na ɛde tumi a ɛyera bɛba. Sɛ wɔbɔ charge wie a, LiFePO4 a wɔmfa nni dwuma no bɛkɔ so atra particle no mfinimfini.

Sɛ yesusuw sɛ lithium ions betumi akɔ mu bere koro mu na akɔ mu wɔ mmeae pii a, Andersson ne ne mfɛfo. de mosaic nhwɛsoɔ no ho nyansahyɛ maeɛ sɛ wɔmfa nkyerɛkyerɛ tumi a ɛyeraeɛ mfitiaseɛ no mu, sɛdeɛ wɔakyerɛ wɔ Mfonini 4-3b mu no. Mosaic model no kyerɛ sɛ ɛwom sɛ lithium ion intercalation ne deintercalation nhyehyɛe no wɔ LiFePO4/FePO4 two-phase interface no mu de, nanso adeyɛ no betumi asi wɔ beae biara wɔ particle no mu. Bere a wɔrebɔ charge no, FePO4 mantam no trɛw wɔ mmeae ahorow wɔ abɔde nketenkete no so, na saa mmeae yi anoano di nkitaho, na ɛma mmeae a awu pii a wontumi nyɛ ho hwee ba, na ɛnam so ma tumi a ɛwɔ mu no hwere. Bere a wɔreyi nneɛma afi mu no, adeyɛ a ɛdannan no ba, na lithium ions kɔhyɛ FePO4 fã no mu. Ɔfã a ɛwɔ mfinimfini a lithium ions nhyɛ mu no ma tumi a wɔhwere no ba.

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

Wɔyɛɛ nsusuwii nhwɛso abien bere koro mu, nanso core-shell model no yɛ nea nhwehwɛmufo gye tom kɛse, ɛwom sɛ nneɛma pɔtee a ɛwɔ shell ne core no mu no da so ara yɛ akyinnyegye de. Yebetumi agyina saa nhwɛso abien yi so aka sɛ lithium ions ne charge a ɛtrɛw no ne nneɛma a ɛho hia ma electrode ade no nyinaa a wɔde bedi dwuma yiye. Wɔ lithium iron phosphate cathode nneɛma a wɔyɛ mu no, wɔbɔ mmɔden sɛ wobenya nneɛma nketenkete a ne kɛse yɛ pɛ (nanoscale anaa microporous), denam carbon coating (nanocarbon film) ne ion doping so de ama conductivity ne lithium ion diffusion atu mpɔn.

Ɛnam nteaseɛ a emu dɔ wɔ LiMPO nneɛma ho nti, wɔhunuu sɛ saa nhwɛsoɔ mmienu yi buu wɔn ani guu anisotropic su kɛseɛ a ɛwɔ lithium ion akwantuo mu wɔ LiMPO nneɛma mu no so. Laffont de "New Core-shell Model" ho nyansahyɛ mae sɛ wɔmfa nsiesie "core-shell model" no sintɔ ahorow. Delmas de eyi sii LiFePO nneɛma nketenkete a ɛwɔ depletion tebea ahorow mu ho ade na ɔhyɛɛ nyansa sɛ wɔnyɛ "Domino-cascade Model," a ɛkyerɛkyerɛ nanoscale nneɛma nketenkete no charge ne discharge adwumayɛ mu yiye, sɛnea wɔada no adi wɔ Mfonini 4-4 mu no.

Ɛmfa ho sɛ nsonsonoeɛ kɛseɛ wɔ nhwɛsoɔ a yɛadi kan aka ho asɛm no ntam no, asɛm titire no da nkɔmhyɛ ne ne su a ɛwɔ -fase ntam nkitahodiɛ no mu. Esiane sɛ lithium a wɔde hyɛ mu/yiyi mu no kinetics ne phase transition no gyina nneɛma no mu nneɛma nketenkete kɛse, ne nsɛso, ne ne nipadua mu nneɛma so kɛse nti, ebia atifi hɔ nkɔmmɔbɔ ahorow no (a ntawntawdi a ɛda nhwɛso ahorow ntam ka ho) no fi sɔhwɛ tebea horow a ɛnnɔɔso.

Ɛnam sɛ wɔayɛ microscopy ne spectroscopy nti, wɔahu solid solution reactions ne intermediate phases wɔ LiMPO4 nneɛma no phase nsakraeɛ mu, a ɛkyerɛ sɛ phase nsakraeɛ kwan foforɔ bi bɛtumi aba wɔ LiMPO4 nneɛma mu. Wɔ solid solution reactions a wɔtaa yɛ mu no, cell parameters ne cell volume da nsakrae a ɛkɔ so adi wɔ phase transitions mu. Ɛnam sɔhwɛ tebea horow bi a ɛyɛ den ne akwan a wɔfa so kyerɛ su, te sɛ ultra-nsu nketenkete (nanoscale) ne high-rate charge-discharge (boro 10C) so no, wɔahu solid solution reactions ne intermediate phases a ɛwɔ hɔ wɔ LiMPO4 mu.

Phase nsakrae bere a charge-discharge nhyehyɛe ahorow wɔ dan mu hyew mu. Lithium-ion batere da reversibility pa adi wɔ charge-discharge cycles mu, a ɛne structure nsɛsoɔ a ɛwɔ phase tebea horow no ntam wɔ lithium-ion deintercalation/intercalation akyi no wɔ abusuabɔ. Wɔ charge-discharge akwan mu no, battery no tumi a ɛporɔw no ne phase transition kinetics no wɔ abusuabɔ kɛse. Sɛnea LiFePO4 nhyehyɛe kyerɛ no, [100]pmnb akwankyerɛ no ye sen biara ma lithium-ion tu, na ntamgyinafo a ɛda fa abien no ntam no fa c-axis no so wɔ charge-discharge nhyehyɛe ahorow mu.

(1) Nkwa Po4/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, Li11δFePO4 no diffraction peak no fi ase yera, na diffraction peak a FePO4 de ba no ahoɔden kɔ soro nkakrankakra. Nea ɛne no bɔ abira no, bere a wɔde lithium ions hyɛ mu no, diffraction peak a FePO4 de ba no ahoɔden so tew nkakrankakra, na diffraction peak a Li10δFePO4 de ba no ahoɔden kɔ soro nkakrankakra.

(2) Li1FePO1/Li11yFePO2Li1FePO4 wɔ dan mu hyew mu yɛ Fe30/Fe20 afrafra-valence mesophase Li1FePO4/Li11 FePO4 afrafra. na egyina hɔ ma carrier density ne hopping probability bere a charge ne discharging, sɛnea ɛte biara. Powder neutron diffraction daa no adi sɛ gyinapɛn a eye sen biara ma ne yɛ 0.05 ne 0.11, sɛnea ɛte biara. Nneɛma te sɛ ion doping, ɔhyew, transition metal, particle size, ne non-equilibrium states wɔ overpotential nyinaa nya ne . Nkɔanim a ɛsom bo na ɛbɛma kinetic adwumayɛ a electrode reaction no atu mpɔn bere a charge ne dischargeing wɔ dan mu hyew.

Wɔ 450℃, Li1FePO4 aduru a ɛyɛ den wɔ hɔ, bere a wɔ dan mu hyew mu no, metastable phases abien wɔ hɔ: Li1.15 FePO4 ne Li1.1FePO4. Sɛ ɛboro digrii 500 a, Li1FePO4 fi ase porɔw yɛ nneɛma a ɛnyɛ-olivine; phosphates anaa phosphides yi mu nneɛma ne nea ɛwom no gyina x bo so. Wɔ digrii 400 ne 500 ntam no, Li1FePO4 a ɛyɛ den nkutoo na ɛwɔ hɔ.

Nsakrae a ɛba bere a wɔreyɛ onwini no yɛ nea emu yɛ den koraa sen nea ɛba bere a wɔreyɛ hyew no. Nneɛma a ɛwɔ afrafrade no mu bere a ɛredwo no gyina x bo ne ɔhyew kwan a wɔfa so yɛ no so. Sɛ ɛyɛ nwini a, Li1FePO4 di kan porɔw yɛ afrafra a ɛyɛ nneɛma abien a ɛnyɛ-olivine, a ne nsusuwii gyina ɔhyew ne x bo a edi kan no so. Sɛ ɔhyew no ba fam (140±20℃) a, abien-fase nhyehyɛe no bɛyɛ nhyehyɛe a ɛyɛ den kɛse, a LiFePO4 ne FePO4 ne olivine-su nnuru afoforo abien, Li11FePO4 ne Li12FePO4 bom tra. Saa afrafrade yi a ɛbɔ akwakoraa wɔ dan mu hyew mu no ma anan-fase nhyehyɛe no dan nkakrankakra ma ɛbɛyɛ abien-fase nhyehyɛe a ɛyɛ LiFePO4 ne FePO4.

Battery reaction mechanism

FePO4 wɔ nhyehyɛe ahorow pii mu: 1 Bere a wɔayi LiFePO4 afi mu koraa akyi no, orthorhombic FePO4 na ɛba; 2 Triclinic FePO4 wɔ quartz-te sɛ nhyehyɛe, a cations nyinaa tetrahedral ayɛ biako; 3 Wobetumi asiesie Monoclinic ne orthorhombic FePO4 afi wɔn hydrates mu. Saa FePO4 a ɛyɛ ahwehwɛ yi nyinaa, ne FePO4 a ɛnyɛ nsɛso nso, wobetumi adan no triclinic FePO4 bere a wɔayɛ no hyew no.

Nsakrae a efi LiFePO4 kɔ FePO4 mu no yɛ brɛoo na enni mũ, nanso edi mũ bere a ɔhyew no boro digrii 500 no . Wɔ batere adwumayɛ tebea horow mu no, cathode ade no yɛ nea ɛyɛ den wɔ kinetically mu. Bere a wɔreyɛ LiFePO4 no, ɛho hia sɛ wɔhwɛ hu sɛ FePO4 nni hɔ. Sɛ ɛwɔ hɔ a, wɔbɛma triclinic FePO4 aba bere a wɔayɛ no hyew no, na ɛde ahwehwɛ a ɛnyɛ -electrochemically active glassy phase bɛba wɔ nneɛma no ani wɔ ɔhyew a ɛkorɔn mu.

Ion doping betumi ama nneɛma a ɛde nsu fa mu no atu mpɔn. Wɔnam ion doping so nya P-type semiconductor conductive nneɛma a conductivity du 10−2 S/cm. Doping yɛ adeyɛ a ɛyɛ den yiye: ɔkwan biako so no, density functional theory (DFT) akontaabu a ɛfa ɛlɛtrɔnik nhyehyɛe a ɛwɔ LiFePO4 ase wɔ local density approximation (LDA) ne generalized gradient approximation (GGA) ase no kyerɛ sɛ ɛsɛ sɛ ade no da su ahorow adi sɛ ɛyɛ dade anaa semiconductor ade, a conduction band ne valence band trɛw bɛyɛ 0.3 eV, a ɛyɛ a ɛne conductivity a ɛba fam a wɔahu ankasa no nhyia. Ɔkwan foforo so no, sɛ yesusuw nkitahodi a ɛda ɛlɛtrɔnik kyinhyia ne Coulomb nkitahodi mu wɔ ion doping akyi a, valence band nhyehyɛe a ɛkɔ anim no yɛ nea wobetumi ayɛ wɔ nsusuwii mu.

DFT akontabuo a ɛfa Mg- anaa Cr-doped LiFePO4 kyerɛ sɛ ɛlɛtrɔnik tebea a ɛyɛ den sen biara no bɛn Fermi level, a ɛkyerɛkyerɛ dadeɛ conductivity a ɛwɔ doped ade no mu. Ebia nsakrae a ɛba wɔ conductivity mu a ion doping de ba no ne nneɛma a edidi so yi wɔ abusuabɔ:

1) Wɔde dade ayɛ charge carrier regions no anoano.

2) Ion doping ma valence band ne conduction band no trɛw yɛ teateaa.

3) Sɛ ɛboro dodow bi a ɛho hia so a, electron wavefunction a ɛwɔ dopant ions no mu no ma wɔyɛ conduction band.

4) Dopant ions no su, ne dodow, ne ne kyekyɛ.

5) Wɔ M-O dade oxide pii mu no, dade a ɛkɔ baabiara pue bere a M-M nkitahodi kwan no nnu 3 × 10−10 m.

6) Wɔ synthesis mu no, organic carbon a wɔde ka ho no ma carbon kata ade no so, na ɛma wonya conduction kwan a etu mpɔn.

7) Fe2P a ɛda adi. Bere a wɔreyɛ nneɛma no, carbon a ɛboro so a wɔde ka ho no ma phosphate no so tew.

Ion doping and conductivity

8) Fe3+/Fe2+ redox baanu no yɛ adwuma sɛ ade a ɛma LiFePO4 so tew.

LiFePO4 da sɛnea ɛne electrolytes a wɔtaa de di dwuma no yɛ adwuma adi. Electrochemical suban a ade no yɛ no ne ne soro chemistry wɔ electrolyte no mu wɔ abusuabɔ kɛse. Mpɛn pii no, pasivation film bi ba wɔ ade no ani. Saa sini yi ma lithium-ion trɛw yɛ mmerɛw, esiw nneɛma a ɛyɛ adwuma a ɛyera ano, na ɛsɛ sɛ egyina nsakrae a ɛba ne kɛse ne ne soro bere a wɔde lithium-ion hyɛ mu/yi mu no ano. LiFePO4 a wɔde carbon-kata so no kura nneɛma te sɛ LiF, LiPF₆, Li1Fᵧ−, ne Li1POᵧFᶻ−.

Mpɛn pii no, alkyl carbonates ne lithium nkyene na ɛwɔ electrolytes a wɔtaa de di dwuma mu. Cathode ade no fa nneyɛe pii a ebetumi aba wɔ electrolyte no mu. Sɛ nhwɛso no, wɔ LiPF3 solutions mu no, acid-base reaction a ɛda LiFePO4 ne HF kakraa bi ntam no yɛ nea wontumi nkwati. HF a ɛwɔ electrolyte no mu no wɔ nkɛntɛnso bɔne abien: nea edi kan no, dade ions ne proton ahorow a wɔde si ananmu no; na nea ɛto so abien no, Li ions ne F ions a ɛyɛ adwuma wɔ abɔde nketenkete no ani ma ɛyɛ LiF, a esiw Li+ trɛw kwan.

Dade ions no tew wɔ electrolytes mu. Sɔhwɛ ahorow a wɔyɛe wɔ dade ion a wɔpete LiFePO4 mu wɔ electrolytes ahorow mu no daa nea edidi so yi adi:

1) Wɔ electrolytes a acidic efĩ nni mu mu no, wɔ ɔhyew a ɛkɔ soro mpo mu no, dade ions a ɛpete ne ade a ɛyɛ adwuma no dodow a ɛyera a efi mu ba no yɛ nea wontumi mmu ani ngu so.

2) solution acidity a ɛkorɔn ma dade ion a ɛyɛ mmerɛw sɛ ɛbɛpete.

3) Ɔhyew a ɛkɔ soro no ma ɛyɛ mmerɛw sɛ dade ion bɛpete.

4) Carbon a ɛkɔ soro wɔ ade no mu no ma nneɛma no gyina pintinn kɛse.

Beae a ade a ɛyɛ adwuma ne nea ɛkyekyere no di nkitaho no na ɛyɛ mmerɛw sɛ ɛbɛsɛe. Wobetumi akwati saa nsɛe yi denam alkaline mesophase a wɔde bedi dwuma anaasɛ acidic scavenging additives a wɔde bedi dwuma so. Wɔ lithium-ion batere a wɔde LiFePO4 di dwuma sɛ cathode ade mu no, wobetumi de electrolytes a ɛnyɛ -acidic anaasɛ carbon a wɔde ka ho anaasɛ wɔde kata LiFePO4 so adi dwuma de asiw dodow a ɛyera ano.

Wɔnnya nte LiFePO4 cathode nneɛma no su a ɛkɔ so no ase yiye. Wɔtaa gye di sɛ abɔdeɛ nketenkete kɛseɛ ne ne kyekyɛ, conductivity, ion diffusion, kinetics wɔ phase transitions (charge-discharge process), ne carbon coating/doping nyinaa ka battery no adwumayɛ wɔ charge-discharge rates ahodoɔ mu. Carbon doping a ɛyɛ pɛ kyerɛ sɛ wobetumi de lithium ions ne electrons ahyɛ mu na wɔayi afi mu wɔ beae koro wɔ ade a ɛyɛ adwuma no mu, na ɛtew electrode polarization so.

(1) Nkɛntɛnso a Conductivity nya wɔ Capacity so LiFePO4 a ɛho tew no conductivity a ɛba fam no ma battery no ahoɔden a ɛkɔ soro-rate discharge tumi no so tew tẽẽ. LiFePO4 a ɛho tew no nsuo a ɛkɔ mu no bɛyɛ 10−9 S/cm, na tumi a ɛtwetwe no so tew kɛseɛ firi 148 mA·h/g wɔ 0.2C a ɛfiri mu ba kɔ 85 mA·h/g wɔ 5C a ɛfiri mu ba. Ɛnyɛ bere nyinaa na cathode ade no tumi a ɛkɔ soro-rate discharge tumi no kɔ soro bere a conductivity kɔ soro no. Wɔ conductivity a ɛba fam mu no, conductivity a ɛkɔ soro no ma electrochemical kinetics a ɛwɔ ade no mu no tu mpɔn. Sɛ ade no conductivity boro bo pɔtee bi a ɛho hia a, conductivity nyɛ ade a ɛkyerɛ ade no rate tumi bio. LiFe0.₀.1PO4 (1.0 × 10−7 S/cm), a ne conductivity a ɛba fam no, da tumi a ɛkorɔn-rate a ɛma nsuo gu mu yie sene LiFePO4 (4.0 × 10−6 S/cm), a tumi a ɛma nsuo gu mu yɛ 90 mA·h/g ne 55 mA·h/g, sɛnea ɛte biara, wɔ 10C discharge rate mu. Eyi kyerɛ sɛ ebia na lithium-ion trɛw asi conductivity ananmu sɛ ade titiriw wɔ electrochemical su a ɛwɔ lithium-ion battery mu.

(2) Lithium-ion Diffusion Lithium-ion diffusion nam nneɛma a ɛwɔ mu ne akyi nyinaa na ɛkyerɛ. Nneɛma a ɛwɔ akyi no bi ne nneɛma nketenkete no kɛse, sɛnea wɔkyekyɛ, ne sɛnea ɛte. Nneɛma a ɛwɔ mu no kyerɛ lithium-ion diffusion coefficient titiriw. Lithium-ion diffusion coefficient no yɛ botaeɛ a ɛkɔ so daa; tumi a lithium ions tumi trɛw no so tew bere a nneɛma nketenkete no kɛse kɔ soro efisɛ lithium ions a ɛtrɛw wɔ abɔde nketenkete no mu no kɔ soro. Lithium ions tumi a ɛtrɛw no ne abɔde nketenkete no kɛse ahinanan no hyia wɔ ɔkwan a ɛne no bɔ abira so na ɛne lithium-ion trɛw nsusuwii no hyia tẽẽ. Nneɛma nketenkete kɛse wɔ nkɛntɛnso kɛse wɔ lithium-ion trɛw so sen diffusion coefficient. Ɛsɛ sɛ wɔde akontabuo akontabuo a ɛfa lithium-ion diffusion coefficient ho no ka susudua akwan pɔtee ne nsusuiɛ nhwɛsoɔ ho. Akwan titiriw a wɔfa so susuw nneɛma ne galvanostatic titration (GITT) ne electrochemical impedance spectroscopy (EIS anaa AC Impedance).

(3) Nneɛma abien-afã scale electrode: Thin-film electrode ma electrode dwumadi yɛ kɛse denam soro beae a ɛkɔ soro no so. Wɔ thin-film electrodes mu no, electrons hyɛn current collector no mu bere a lithium ions hyɛn electrolyte no mu fi ɔkwan a ɛne no bɔ abira so. Sɛ wɔhyehyɛ FePO4 layer no a, ɛlɛtrɔnik a ɛko tia no so tew, bere a lithium-ion a ɛko tia lithium-ion kankan no kɔ soro. FePO4 di kan yɛ nucleate wɔ ahwehwɛ sintɔ ahorow mu na afei enyin wɔ afã horow nyinaa, na esiw lithium-ion trɛw kosi sɛ lithium ions ntumi nguan nkɔ [100] kwan no so.