Menene tsarin amsa batir? {0} Polinovel

Menene tsarin amsa batir?

A halin yanzu, babu daidai kuma daidai fahimtar tsarin amsawar electrochemical na LiFePO₄ a cikin masana'antar. Aikace-aikacen anion composite (PO₄)³⁻ yana sanya baƙin ƙarfe{1} tushen mahadi ya zama kyakkyawan ɗan takara don lithium{2}} ion baturi cathodes. Koyaya, tsarin lu'ulu'u na LiFePO₄ yana iyakance ƙarfin aiki da aikin lithium - ion watsawa, yana haifar da raguwar aikin sinadarai na lantarki. Ba kamar kayan da aka zayyana ba, cajin -madaidaicin madaurin LiMPO₄ yawanci yana da fili mai faɗin fili, wanda shine siffa ta al'ada ta halayen lokaci biyu{7}, ma'ana cewa tsarin canjin lokaci tsakanin LiMPO₄ da MPO₄ yana faruwa a lokacin lithium{8} ion intercalation/deintercalation.

LiFePO4 yana jurewa tsarin amsawa na lokaci biyu{1} yayin caji da fitarwa a cikin baturi, watau

Reaction mechanism model

Yayin caji, Li⁺ yana ƙaura daga Layer FeO₆, ya wuce ta hanyar lantarki, kuma ya shiga mummunan lantarki. Fe²⁺ yana da oxidized zuwa Fe³⁺, yayin da electrons ke tafiya daga da'irar waje zuwa madaidaicin wutar lantarki ta hanyar wakilin gudanarwa da mai tarawa na yanzu. Tsarin fitarwa shine baya.

Don kwatanta wannan - hali na lokaci biyu, Padhi da Goodenough et al. da farko ya ba da shawarar “core{2}}samfurin harsashi,” wanda ya nuna cewa tsarin haɗin gwiwar lithium{3} ion yana faruwa a LiFePO₄/FePO₄ sau biyu-, kamar yadda aka nuna a hoto 4-3a.

Yayin caji, ƙirar LiFePO₄/FePO₄ yana ci gaba da motsawa daga saman zuwa tsakiya, yana turawa zuwa ainihin. Li⁺ yana ci gaba da ƙaura zuwa waje, kuma LiFePO₄ na waje yana ci gaba da canzawa zuwa FePO₄. Lithium ions da electrons suna ci gaba da wucewa ta cikin sabbin hanyoyin sadarwa na zamani guda biyu{2} don kiyaye ingantaccen halin yanzu, amma adadin yaɗuwar lithium{3} ion yana dawwama ƙarƙashin wasu sharuɗɗa. Yayin da mu'amalar da ke tsakanin sassan biyu ke raguwa, yaduwar ion lithium ba zai wadatar ba a ƙarshe don kiyaye ingantaccen halin yanzu. The LiFePO₄ a cikin barbashi core ba za a cikakken amfani, sakamakon iya aiki asara. Bayan caji ya cika, LiFePO₄ da ba a yi amfani da shi ba zai kasance a tsakiyar ɓangaren.

Idan akai la'akari da cewa lithium ions na iya yin tsaka-tsaki a lokaci guda kuma ya bambanta a shafuka da yawa, Andersson et al. ya ba da shawarar ƙirar mosaic don bayyana asarar ƙarfin farko, kamar yadda aka nuna a hoto 4{3}}3b. Mosaic model posits cewa ko da yake lithium ion intercalation da deintercalation tsari ne a LiFePO₄/FePO₄ biyu -lokaci dubawa, da tsari na iya faruwa a kowane wuri a cikin barbashi. A lokacin caji, da FePO₄ yankin kara girma a daban-daban maki a kan barbashi, da kuma gefuna na wadannan yankuna giciye-lamba, haifar da yawa unreactable matattu zones, don haka haifar da iya aiki hasãra. A yayin fitar da ruwa, abin da ya biyo baya yana faruwa, tare da ions lithium suna shiga cikin lokaci na FePO₄. Sashin da ke ainihin inda ions lithium ba a haɗa su yana haifar da asarar iya aiki.

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

An ƙirƙira ƙirar ƙira guda biyu a lokaci guda, amma ainihin ƙirar harsashi - ana samun karɓuwa sosai a wurin masu bincike, kodayake takamaiman kayan harsashi da ainihin suna ci gaba da jayayya. Dangane da waɗannan nau'ikan guda biyu, ana iya ƙarasa da cewa watsawar ion lithium da caji sune mahimman dalilai don aikace-aikacen aikace-aikacen gabaɗayan lantarki. A cikin shirye-shiryen lithium baƙin ƙarfe phosphate cathode kayan, kokarin da ake yi don samun barbashi da kananan da kuma uniform size (nanoscale ko microporous), ta yin amfani da carbon shafi (nanocarbon film) da ion doping don inganta conductivity da lithium ion watsawa.

Tare da zurfin fahimtar kayan LiMPO, an gano cewa waɗannan samfuran biyu sun yi watsi da halayen anisotropic na jigilar lithium ion a cikin kayan LiMPO. Laffont ya ba da shawarar "Sabon Core{1} Model" don gyara gazawar "core{2}}samfurin harsashi." Gina kan wannan, Delmas ya yi nazarin barbashi na LiFePO a cikin jahohi daban-daban na raguwa kuma ya ba da shawarar "Domino{4}} Model Cascade," wanda ke bayyana yadda sauri caji da fitar da barbashi na nanoscale, kamar yadda aka nuna a cikin Hoto 4-4.

Duk da bambance-bambancen bambance-bambancen da ke tsakanin samfuran da aka ambata, babban batun yana cikin tsinkaya da sifa na mu'amalar lokaci biyu-. Tun da kinetics na lithium sakawa / cirewa da kuma canjin lokaci sun dogara sosai akan girman barbashi, ilimin halittar jiki, da kaddarorin physicochemical na kayan, tattaunawar da ke sama (ciki har da rikice-rikice tsakanin samfura) na iya zama saboda rashin isasshen yanayin gwaji.

Tare da ci gaban microscopy da spectroscopy, an lura da ingantattun halayen bayani da kuma matakan tsaka-tsaki yayin jujjuyawar lokaci na kayan LiMPO4, yana nuna cewa wani tsarin canjin lokaci na iya kasancewa a cikin kayan LiMPO4. A cikin halayen daɗaɗɗen bayani na yau da kullun, sigogin tantanin halitta da ƙarar tantanin halitta suna nuna ci gaba da canje-canje yayin canjin lokaci. Ta wasu matsananciyar yanayin gwaji da hanyoyin ƙirƙira, kamar matsananci{4}}ƙananan barbashi (nanoscale) da babban cajin ƙima (a sama da 10C), an lura da ƙaƙƙarfan halayen bayani da wanzuwar tsaka-tsaki a cikin LiMPO4.

Canje-canjen lokaci yayin caji{0}} tafiyar matakai a yanayin zafi. Lithium -batir ion suna nuna juyi mai kyau yayin caji{3}} zagayowar zagayowar, wanda ke da alaƙa da tsarin kamanni tsakanin jahohin zamani bayan lithium{4}} ion deintercalation/intercalation. Yayin aiwatar da aikin caji{6}}, lalata ƙarfin baturi yana da alaƙa da kusancin motsin motsin lokaci. Bisa ga tsarin LiFePO4, hanyar [100]pmnb ta fi dacewa ga ƙaura na lithium, kuma mahaɗin tsakanin sassan biyu yana tafiya tare da c{11}}axis yayin caji{12}} tafiyar matakai.

(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, Diffraction kololuwa na Li₁₋δFePO₄ fara bace, da kuma tsananin diffraction kololuwa samar da FePO₄ a hankali yana ƙaruwa. Sabanin haka, yayin da aka shigar da ions lithium, ƙarfin kololuwar kololuwar da FePO₄ ke samarwa yana raguwa a hankali, kuma ƙarfin kololuwar ɓarna da Li₁₋δFePO₄ ke samarwa a hankali yana ƙaruwa.

(2) LiₓFePO₄/Li₁₋yFePO₄LiₓFePO₄ a dakin zafin jiki shine cakuda Fe³⁺/Fe²⁺ gauraye -valence mesophase LiₐFePO₄/Li₁₋ FePO₄. kuma suna wakiltar yawa mai ɗauka da yuwuwar hopping yayin caji da fitarwa, bi da bi. Powder neutron diffraction bayyana cewa mafi kyau duka dabi'u don kuma su ne 0.05 da kuma 0.11, bi da bi. Abubuwa kamar ion doping, zafin jiki, karfen canji, girman barbashi, da marasa daidaiton jihohin da ba su da ƙarfi duk suna shafar ƙimar da . Haɓaka dabi'u na kuma zai inganta aikin motsa jiki na amsawar lantarki yayin caji da fitarwa a zafin jiki.

A 450 digiri, wani m bayani na LiₓFePO₄ wanzu, yayin da a dakin da zazzabi, biyu metastable bulan wanzu: Li₀.₇₅FePO₄ da Li₀.₅FePO₄. Sama da digiri 500, LiₓFePO₄ ya fara bazuwa zuwa abubuwan da ba - olivine mahadi; abun ciki da abun ciki na waɗannan phosphates ko phosphides sun dogara da ƙimar x. Tsakanin digiri 400 da 500, kawai ingantaccen bayani na LiₓFePO₄ ya wanzu.

Canje-canje a lokacin sanyaya sun fi rikitarwa fiye da na lokacin dumama. Abubuwan da ke tattare da cakuda yayin sanyaya ya dogara da ƙimar x da tsarin thermal. Bayan sanyaya, LiₓFePO₄ na farko yana rubewa zuwa gauraya nau'i biyu marasa{2}, wanda adadinsu ya dogara da ƙimar farko na zafin jiki da x. Lokacin da zafin jiki yana ƙasa (digiri 140 ± 20), tsarin guda biyu- ya zama tsarin da ya fi rikitarwa, wanda LiFePO₄ da FePO₄ suka kasance tare da wasu olivine guda biyu{7}} nau'in mahadi, Liₓ₁ FePO₄ da Liₓ₂ FePO₄. Tsufa wannan cakuda a yanayin zafi yana haifar da tsarin lokaci guda huɗu{9} don rikiɗawa a hankali zuwa tsarin lokaci biyu{10} na LiFePO₄ da FePO₄.

Battery reaction mechanism

FePO₄ yana wanzuwa a cikin sifofi da yawa: ① Bayan kammalawar LiFePO₄, an kafa FePO₄ orthorhombic; ② Triclinic FePO₄ yana da ma'adini{0}}kamar tsari, tare da daidaita dukkan cations tetrahedral; Ana iya shirya ③ Monoclinic da orthorhombic FePO₄ daga hydrates daban-daban. Duk wadannan crystalline siffofin FePO₄, kazalika da amorphous FePO₄, za a iya canza zuwa triclinic FePO₄ kan dumama.

Canji daga LiFePO₄ zuwa FePO₄ yana jinkiri kuma bai cika ba, amma cikakke lokacin da zafin jiki ya wuce digiri 500. Ƙarƙashin yanayin aiki na baturi, kayan cathode yana da kwanciyar hankali. A lokacin kira na LiFePO₄, yana da mahimmanci don tabbatar da rashin FePO₄. Idan akwai, za a samar da triclinic FePO₄ akan dumama, wanda zai haifar da rashin aikin gilashin lantarki a saman kayan a yanayin zafi.

Ion doping na iya inganta halayen kayan aiki. P-nau'in kayan sarrafa semiconductor tare da ƙarfin aiki da ya kai 10⁻² S/cm ana samun su ta hanyar ion doping. Doping tsari ne mai matukar rikitarwa: a gefe guda, ka'idar aikin aiki mai yawa (DFT) lissafin tsarin lantarki na LiFePO₄ a ƙarƙashin ƙimar ƙimar gida (LDA) da ƙimar gradient gabaɗaya (GGA) yana nuna cewa kayan yakamata su nuna halaye na ƙarfe ko semiconductor abu, tare da bandeji mai ƙarfi da ƙarancin ƙarancin ƙarfi. conductivity a zahiri gano. A gefe guda, la'akari da hulɗar electron orbitals da Coulomb hulɗar bayan ion doping, ingantaccen tsarin band na valence abu ne mai yiwuwa.

Ƙididdigar DFT na Mg{0}} ko Cr{1}}doped LiFePO₄ ya nuna cewa matsakaicin yawan adadin jihohin lantarki yana kusa da matakin Fermi, wanda ke bayyana ƙarfin ƙarfin ƙarfe na kayan kara kuzari. Canje-canjen halayen da ion doping ya haifar na iya kasancewa da alaƙa da abubuwa masu zuwa:

1) Gefuna na yankuna masu ɗaukar kaya suna ƙarfe.

2) Ion doping yana rage nisa na band ɗin valence da band conduction.

3) Wucewa wani mahimmanci mai mahimmanci, aikin wutar lantarki na dopant ions yana haifar da samuwar band conduction.

4) Nau'in, maida hankali, da rarraba ions na dopant.

5) A cikin M- Oxides na ƙarfe da yawa, ƙungiyar sarrafa ƙarfe tana bayyana lokacin da nisan haɗin M{2}M bai wuce 3 × 10⁻¹⁰ m.

6) A lokacin haɓakawa, haɓakar carbon carbon yana haifar da murfin carbon na kayan, ƙirƙirar hanyar gudanarwa mai tasiri.

7) Bayyanar Fe₂P. A lokacin hadawa, ƙari da wuce haddi na carbon yana rage phosphate.

Ion doping and conductivity

8) Fe³⁺/Fe²⁺ redox biyu yana aiki azaman mai kara kuzari a rage LiFePO₄.

LiFePO₄ yana nuna reactivity tare da yawan amfani da electrolytes. Halin lantarki na kayan abu yana da alaƙa sosai tare da sinadarai na saman da ke cikin electrolyte. Gabaɗaya, fim ɗin wucewa yana buɗe akan saman kayan. Wannan fim ɗin yana sauƙaƙe yaduwar lithium{3} ion, yana hana asarar abu mai aiki, kuma dole ne ya jure ƙarar girma da canje-canjen saman yayin shigar lithium{4}}ingantawa/haɗewa. Carbon -mai rufi LiFePO₄ fina-finan saman sun ƙunshi mahadi kamar LiF, LiPF₆, LiₓFᵧ⁻, da LiₓPOᵧFᶻ⁻.

Na kowa electrolytes yawanci sun ƙunshi alkyl carbonates da lithium salts. Kayan cathode yana jurewa da yawa yiwuwar halayen a cikin electrolyte. Misali, a cikin maganin LiPF₆, acid{2}}asashen amsa tsakanin LiFePO₄ da adadin HF ba zai yuwu ba. Kasancewar HF a cikin electrolyte yana da lahani guda biyu: na farko, canjin canji tsakanin ions baƙin ƙarfe da protons; Na biyu kuma, yadda Li ions da F ions suka yi a jikin barbashi don samar da LiF, wanda ke hana Li⁺ yaduwa.

Iron ions narke a cikin electrolytes. Gwaje-gwaje akan narkar da ion baƙin ƙarfe na LiFePO₄ a cikin electrolytes daban-daban sun bayyana kamar haka:

1) A cikin electrolytes free of acidic gurbatawa, ko da a high yanayin zafi, narkar da baƙin ƙarfe ions da sakamakon taro asarar da aiki abu ne sakaci.

2) Higher bayani acidity take kaiwa zuwa sauki baƙin ƙarfe ion rushewa.

3) Mafi girman zafin jiki yana haifar da sauƙin narkewar baƙin ƙarfe.

4) Babban abun ciki na carbon a cikin kayan yana haifar da kwanciyar hankali mafi girma.

Yankin lamba tsakanin abu mai aiki da mai ɗaure ya fi saurin lalacewa. Ana iya guje wa wannan lalata ta hanyar amfani da mesophase na alkaline ko amfani da abubuwan da ke lalata acidic. A cikin batirin lithium{2} ion da ke amfani da LiFePO₄ azaman kayan cathode, ba{3}}acid electrolytes ko ƙari na carbon ko shafi na LiFePO₄ ana iya amfani da su don hana asarar jama'a.

Halayen motsin motsa jiki na kayan LiFePO₄ cathode ba a fahimta ba tukuna. An yi imani da cewa girman barbashi da rarrabawa, haɓakawa, yaduwar ion, motsin motsa jiki yayin canjin lokaci ( caji -tsarin fitar da ruwa), da murfin carbon/doping duk suna shafar aikin baturi akan caji daban-daban{2}}yawan fitarwa. Uniform carbon doping yana nufin cewa ana iya shigar da ions lithium da electrons da fitar da su a wuri ɗaya a cikin kayan aiki, yana rage polarization na lantarki.

(1) Tasirin Ƙarfafawa akan Ƙarfin Ƙarfin ƙarfin aiki na LiFePO₄ mai tsafta kai tsaye yana haifar da raguwa a babban ƙarfin fitarwa na baturi. Matsakaicin tsaftar LiFePO₄ yana kusan 10⁻⁹ S/cm, kuma ƙarfin fitarwa ya ragu sosai daga 148 mA·h/g a ƙimar fitarwa na 0.2C zuwa 85 mA·h/g a ƙimar fitarwa na 5C. Babban{9}}ƙarar fitarwa na kayan cathode ba koyaushe yana ƙaruwa tare da haɓaka aiki ba. A low conductivity, karuwa a conductivity inganta electrochemical motsi na abu. Lokacin da ƙayyadaddun kayan aiki ya zarce ƙayyadaddun ƙima mai mahimmanci, ƙaddamarwa ba ita ce ke ƙayyade ƙimar ƙimar kayan ba. LiFe₀.₉Ni₀.₁PO₄ (1.0 × 10⁻⁷ S/cm), tare da ƙananan ƙarfin aiki, yana nuna mafi kyawun ƙarfin fitarwa fiye da LiFePO₄ (4.0 × 10⁻⁶ S/cm), tare da ƙarfin fitarwa na 90m/Ah/h. a 10C fitarwa kudi. Wannan yana nuna cewa watsawar lithium{24}} ƙila ya maye gurbin ɗabi'ar ɗabi'a a matsayin ƙayyadaddun abu a cikin abubuwan lantarki na batirin lithium{25}}.

(2) Lithium -ion Diffusion Lithium -ion diffusion ana ƙaddara ta duka abubuwan ciki da na waje. Abubuwan waje sun haɗa da girman barbashi, rarrabawa, da ilimin halittar jiki. Abubuwan ciki galibi suna nuni ne ga ma'aunin lithium{5}} ion diffusion coefficient. Ƙimar lithium - ion diffusion coefficient yana da ƙima; ikon watsawa na lithium ions yana raguwa tare da ƙara girman barbashi saboda hanyar yaduwar ions lithium a cikin barbashi yana ƙaruwa. Ƙarfin watsawar lithium ions ya yi daidai da murabba'in girman barbashi kuma kai tsaye ya yi daidai da ma'aunin yaduwa na lithium{9}}. Girman ɓangarorin yana da babban tasiri akan yaduwar lithium{11}} fiye da ƙayyadaddun ƙima. Lissafin lambobi na lithium{13}} ion diffusion coefficient dole ne a haɗa shi tare da takamaiman hanyoyin aunawa da ƙira. Babban hanyoyin auna su ne galvanostatic titration (GITT) da electrochemical impedance spectroscopy (EIS ko AC Impedance).

(3) Nau'o'in sikelin ma'auni guda biyu -: Nau'o'in sirara - na'urorin lantarki suna haɓaka aikin lantarki ta hanyar haɓaka sararin samaniya. A cikin sirara - na'urorin lantarki na fim, electrons suna shiga cikin mai tarawa na yanzu yayin da ions lithium ke shiga electrolyte daga kishiyar hanya. Tare da samuwar FePO₄ Layer, juriya ga motsi na lantarki yana raguwa, yayin da juriya ga motsin lithium- ion yana ƙaruwa. FePO₄ na farko yana haifar da lahani na kristal sannan ya girma ta kowane bangare, yana hana yaduwar lithium har sai ion lithium ba zai iya tserewa ta hanyar [100] ba.