Cov roj teeb lithium, txawm tias lawv yog cov roj teeb uas muaj zog lossis cov roj teeb lithium-ion ib txwm muaj, muaj cov qauv zoo sib xws. Muaj ob lub electrodes (zoo thiab tsis zoo) nrog ib tug cais nyob rau hauv nruab nrab. Thaum lub sij hawm them nyiaj, ions migrate los ntawm qhov zoo electrode (cathode) mus rau qhov tsis zoo electrode (anode), thiab thaum lub sij hawm tso tawm, ions migrate rov qab. Vim lub impermeability ntawm daim nyias nyias rau electrons, electrons yuav dhau los ntawm kev sib txuas load (xws li lub teeb) thiab ua rau nws mus rau lub teeb (tshwj xeeb tshaj yog xav paub ntxiv txog kev tsim kho roj teeb, thov mus saib ntawm no).
Cov lus piav qhia no tuaj yeem siv los piav qhia vim li cas cov dej ntws tam sim no hauv cov load, tab sis nws tsis txaus kom nkag siab qhov twg lub zog tuaj. Yog li ntawd, nws yog ib qho tsim nyog yuav tsum tau ua ntau qhov kev tshawb fawb tob txog kev ua haujlwm ntawm cov roj teeb.
Roj teeb qhov rais qhov rais
Ua ntej, nws yog ib qho tsim nyog kom paub meej tias vim li cas qhov voltage ntawm qhov zoo thiab qhov tsis zoo electrodes tuaj yeem ntsuas tau. Lub qhov rais voltage ntawm lithium raws li cov roj teeb yog txhais los ntawm ib feem ntawm cov kev cuam tshuam ntawm qhov tsis zoo thiab qhov zoo electrodes, thiab sib raug zoo nyob ntawm qhov kev tshwm sim tshwm sim. Qhov ntsuas qhov hluav taws xob ntawm ob tug ncej ntawm lub roj teeb yog qhov sib txawv ntawm qhov hluav taws xob tsim los ntawm txhua lub electrode:
UOC=U-negative ncej - U-positive ncej
Qhov hluav taws xob ntawm qhov tsis zoo thiab qhov zoo electrodes tsis yog tus nqi ruaj khov, tab sis nyob ntawm lub xeev them ntawm lub roj teeb. Txawm li cas los xij, qhov tseem ceeb ruaj khov rau electrodes feem ntau muab rau hauv cov ntaub ntawv (xws li LCO ntawm 3.9 V). Cov no feem ntau sib raug rau qhov nruab nrab voltage.
Daim duab qhia tau hais tias yuav ua li cas thiaj li tau txais cov roj teeb zaum kawg los ntawm qhov tsis zoo thiab qhov zoo electrode muaj peev xwm (tso rau hauv cov piv txwv roj teeb LCO|graphite). X-axis qhia txog lithium proportionally khi rau hauv cov electrode. Rau ib qho (zoo tagnrho) roj teeb puv x=1, rau lub roj teeb khoob x=0.
Lub ntsuas hluav taws xob ntawm qhov zoo thiab qhov tsis zoo ntawm lub roj teeb yog tsim los ntawm cov tshuaj tiv thaiv ntawm lithium thiab electrode. Cov hauv qab no yuav muab cov lus piav qhia ntxaws ntxiv uas siv LCO (lithium cobalt oxide) zoo electrode ua piv txwv. Daim duab 2 qhia txog kev tso tawm ntawm LCO|graphite roj teeb. Qhov no yog lithium-ion roj teeb nrog kua electrolyte. Raws li txoj cai, qhov kev tsim no kuj tseem siv tau rau cov roj teeb hauv lub xeev, txawm hais tias LCO thiab cov graphite ntshiab raws li cov ntaub ntawv electrode yog atypical thiab siv cov ntaub ntawv tsim ntxiv (xws li silicon graphite li cov electrode tsis zoo thiab NMC811 raws li qhov zoo electrode).
Qhov hluav taws xob yog tsim los ntawm lithium ion them thiab tawm cov txheej txheem ntawm qhov tsis zoo thiab qhov zoo electrodes. Cov tshuaj tiv thaiv uas pom nyob rau hauv daim duab kuj tseem siv tau rau cov roj teeb uas muaj zog, tab sis cov ntaub ntawv xaiv ntawm no tsis raug thiab tsuas yog siv rau kev siv xwb.
Thaum cov txheej txheem tso tawm, lithium ions tsiv tawm ntawm qhov tsis zoo electrode mus rau qhov zoo electrode. LCO yog qhov zoo electrode nrog cov txheej txheem txheej. Thaum lub sij hawm tso tawm, lithium intercalates ntawm cov cobalt oxide txheej. Qhov sib npaug sib npaug ntawm lithium thiab cobalt oxide yog raws li nram no:
CoO2 + e– + Li+ → LiCoO2
Lub cim ntawm qhov ntsuas hluav taws xob sab nraud yog vim qhov cuam tshuam ntawm cov tshuaj tiv thaiv lithium hauv txhua txheej txheej txheej oxide thiab lub zog tso tawm thaum lub sijhawm exothermic txheej txheem. Nrog kev pab los ntawm lub npe hu ua Nernst sib npaug, qhov voltage ntawm ib nrab ntawm tes yuav raug xam raws li qhov concentration ntawm cov khoom nyob rau hauv lub roj teeb:
Ured {{0}} U(0,red) – (RT / (ze F)) * ln(Red / Ox)
U0,liab: Electrode muaj peev xwm (tuaj yeem nyeem los ntawm cov lus ntawm electrochemical voltage series)
R: Universal Gas qhov qub
T: Kub (Kelvin)
ze: Tus naj npawb ntawm cov hluav taws xob hloov pauv: Tus naj npawb ntawm cov hluav taws xob hloov pauv (lithium tsuas muaj ib qho hluav taws xob valence, yog li ntawm no nws yog 1)
F: Faraday tas mus li
Liab, Ox: Concentration ntawm ntau yam redox reactants
Qhov concentration ntawm redox reactants txawv nrog kev hloov ntawm electrode charge state. Yog li ntawd, lub generated electrode voltage yog qhov tseem ceeb nyob ntawm seb lub electrode muaj peev xwm, uas yog calibrated raws li qhov kub thiab txias lub xeev. Nws yuav tsum tau taw qhia tias qee qhov kev cuam tshuam thib ob kuj tshwm sim hauv lub roj teeb, uas tseem cuam tshuam rau cov khoom siv hluav taws xob, yog li qhov sib npaug saum toj no tsuas yog siv los ua qhov kwv yees thawj zaug xwb.
Vim muaj zog dependence ntawm Nernst kab zauv ntawm electrode muaj peev xwm, peb sim xaiv lub caij nrog lub siab tshaj plaws electrode muaj peev xwm ntawm no. Cov ntsiab lus ntawm sab xis ntawm lub rooj sib tham tau mus txog qhov feem ntau ntawm no vim tias lub vojvoog ionic ntawm cov ntsiab lus tau txo qis, thiab cov khoom siv hluav taws xob muaj zog dua rau cov atomic nucleus. Lub zog nuclear zog yuav ua rau muaj peev xwm electrode ntau dua.
Qhov kev sib txuas no kuj piav qhia vim li cas LCO (LixCoO2) thiab NMC811 yog siv los ua cov khoom siv hluav taws xob zoo. Ntawm cov hlau hloov pauv, cov no yog cov sib txuas nrog qhov siab tshaj plaws ib nrab ntawm tes.
Cov kev txwv ntawm qhov rais voltage
Qhov tso cai voltage ntau ntawm lub roj teeb tsis tsuas yog cuam tshuam los ntawm cov electrodes, tab sis kuj txwv los ntawm lub qhov rais electrochemical ntawm electrolyte siv. Tshwj xeeb tshaj yog cov kua electrolytes tsis tuaj yeem tiv taus qhov hluav taws xob ntau tshaj 4.5V, vim tias cov kab mob parasitic tshwm sim ntawm qhov zoo electrode thiab electrolyte, ua rau qeeb decomposition ntawm electrolyte. Cov roj teeb hauv lub xeev muaj peev xwm tuaj yeem kov yeej qhov kev txwv no hauv lub sijhawm nruab nrab. Piv txwv li, oxide electrolytes muaj qhov tshwj xeeb dav qhov rais, thaum sulfide electrolytes kuj tseem tuaj yeem tiv taus cov hluav taws xob ntau dua nrog cov txheej txheem tiv thaiv ntxiv.
Qhov thib ob tseem ceeb txwv ntawm lub qhov rais voltage yog tias feem ntau nws tsis tuaj yeem siv lub qhov rais tag nrho lub zog hluav taws xob ntawm lub roj teeb. Rau LCO cathodes, nws yog tsis yooj yim sua kom yaj lithium los ntawm cobalt txheej los ntawm ntau tshaj 70%, vim qhov no tsis muaj zog cov neeg kho tshuab qauv ntawm cathode thiab ua rau kom ceev aging. Yog li, piv rau Li / Li +, qhov voltage ntawm LCO roj teeb yog txwv rau 4.2V. Hais txog qhov tsis zoo electrode, feem ntau tsis tuaj yeem tshem tawm tag nrho cov lithium ions, yog li qee qhov lithium ions tseem nyob hauv qhov tsis zoo electrode, yog li txo qhov siab tshaj plaws ua tiav.
Kev txiav txim siab ntawm lub roj teeb muaj peev xwm
Txhawm rau muab lub peev xwm siab tshaj plaws rau lub roj teeb, qhov tsis zoo thiab qhov zoo electrodes yuav tsum tau hloov kho kom zoo thaum lub sij hawm them nqi, tag nrho cov lithium ions tawm ntawm qhov zoo electrode tuaj yeem pom qhov chaw cia hauv cov qauv tsis zoo electrode. Qhov sib piv ntawm qhov loj ntawm qhov tsis zoo electrode thiab qhov loj ntawm qhov zoo electrode yog hu ua N / P piv, qhov N piav qhia txog qhov loj ntawm qhov tsis zoo electrode thiab P piav qhia qhov loj feem ntawm qhov zoo electrode. Vim lub fact tias txhua lithium ion tawm ntawm qhov zoo electrode yuav tsum nrhiav ib txoj hauj lwm ntawm qhov tsis zoo electrode, qhov loj piv N / P ≈ 1. Txawm li cas los xij, nws yog ib qho nyuaj rau lithium ions ib txwm nrhiav ib txoj hauj lwm ntawm qhov tsis zoo electrode. Thaum them nyiaj ceev, lithium ions zoo li tso rau ntawm qhov tsis zoo electrode (lithium plating) vim tias lawv tsis tuaj yeem nrhiav cov haujlwm tsis zoo hauv cov qauv electrode. Vim lithium plating yog ib qho ntawm cov kev puas tsuaj tseem ceeb ntawm cov roj teeb, qhov kev faib ua feem ntawm cov electrodes tsis zoo yog nce me ntsis (N / P ≈ 1.04-1.2), yog li ntawd ions tsis tas yuav mus nrhiav haujlwm tsis ua haujlwm rau ntev dhau lawm.
Lub peev xwm ntawm ntau yam khoom siv feem ntau yog muab rau hauv Ah / kg thiab suav tau. Kev suav tsuas yog xam cov khoom siv. Tshuaj additives, tiv tauj nto, tiv thaiv txheej, thiab lwm yam yog ignored nyob rau hauv lub xam ntawm electrode theoretical muaj peev xwm. Thaum xam, thawj zaug txiav txim siab qhov loj ntawm cov khoom siv electrode (hauv kg / mol). Tus nqi no tuaj yeem xam los ntawm molar mass lossis tau los ntawm lub rooj saib. Rau LCO, molar mass yog 0.09788 kg/mol. Hauv cov kauj ruam thib ob, Avogadro tas li tuaj yeem siv los xam seb muaj pes tsawg molecules tam sim no hauv ib kilogram ntawm cov khoom siv hluav taws xob (rau LCO, qhov no yog 6.15 * 10 ^ 24 atoms ib kilogram).
Raws li cov hlau alkali (cov ntsiab lus ntawm thawj pab pawg tseem ceeb), lithium tsuas muaj ib qho hluav taws xob uas tuaj yeem koom nrog cov tshuaj tiv thaiv. Txhua lub tshuab hluav taws xob muaj cov nqi tsis zoo e. Yog li ntawd, lub lithium atom tuaj yeem tso tus nqi tsim nyog e -.
Txhawm rau suav cov peev txheej, tam sim no yuav tsum xav txog tias thaum lub sijhawm tso tawm, txhua lithium ion yuav hloov cov hluav taws xob los ntawm kev sib txuas. Yog li, lub peev xwm yog qhov khoom ntawm tus nqi ntawm tus nqi nqa los ntawm ib lub atom thiab tus naj npawb ntawm atoms. Rau LCO, qhov no ua rau muaj peev xwm ntawm 274 Ah / kg. Lub peev xwm ntawm lwm cov ntaub ntawv zoo thiab tsis zoo electrode kuj tuaj yeem suav nrog siv tib txoj kev.
Tus nqi suav nruab nrab yog qhov theoretically ua tiav lub zog ceev, tab sis nws feem ntau tsis ze rau tus nqi tiag tiag. Piv txwv li, rau LCO, tsuas yog ib feem ntawm lithium tuaj yeem raug tshem tawm thaum lub sijhawm them nyiaj, yog li lub peev xwm theoretical tsis siv tag nrho, thiab cov txiaj ntsig tau txais hauv kev xyaum yog qis dua. Txawm li cas los xij, cov ntaub ntawv suav tau muab qhov taw qhia zoo rau kev sib piv cov khoom siv sib txawv.
Xaus
Cov lus teb rau lo lus nug ntawm qhov twg lub zog ntawm lithium roj teeb los ntawm qhov tseeb yog qhov tseeb: yog vim li cas yog cov tshuaj tiv thaiv redox uas tshwm sim ntau dua los yog tsawg dua reversibly hauv lub roj teeb thaum them thiab tawm. Vim yog cov qauv ntawm lub roj teeb, cov electrons raug yuam kom tsiv mus rau qhov tsis zoo electrode los ntawm lub charger thaum them nyiaj. Cov txiaj ntsig hloov pauv ua rau lithium ions tseem tsiv mus rau qhov tsis zoo electrode. Thaum lub sij hawm tso tawm, cov txheej txheem yog thim rov qab, nrog rau tam sim no ntws los ntawm kev sib txuas ntawm cov khoom thauj thiab xa hluav taws xob. Qhov hluav taws xob tsim los ntawm lub roj teeb nyob rau hauv ib lub xeev ntawm kev them nqi tuaj yeem suav nrog kev sib npaug Nernst thiab feem ntau yog nyob ntawm qhov concentration ntawm lithium ions ntawm cov electrodes. Qhov ntau lithium ions tsiv mus rau sab zoo electrode, qhov siab dua lawv cov concentration ntawm qhov zoo electrode, thiab qhov sib thooj ntawm cov roj teeb voltage.
Tus nqi zog uas lub roj teeb tuaj yeem muab tau yog nyob ntawm nws lub peev xwm. Lub peev xwm yog cov khoom siv tshwj xeeb sib txawv uas tuaj yeem suav ncaj qha los ntawm cov ntaub ntawv cov ntaub ntawv siv cov kab zauv yooj yim.
Txhua qhov ntsuas tsis suav nrog qhov ntsuas theoretical (qhov siab tshaj plaws) qhov tseem ceeb, uas tsis tau ua tiav hauv kev xyaum. Qhov hluav taws xob yog txwv los ntawm electrolyte, thiab kev siv tag nrho ntawm lub peev xwm yuav cuam tshuam rau txhua yam kev ruaj ntseg ntawm qhov zoo electrode. Tsis tas li ntawd, txhawm rau tiv thaiv cov kab mob parasitic deposition ntawm lithium, cov ntaub ntawv tsis zoo electrode me ntsis yog ib txwm siv tshaj li qhov tsim nyog. Lub hom phiaj ntawm tus txheej txheem tsim qauv zoo yog kom sib npaug tag nrho cov kev cuam tshuam no kom tau txais cov roj teeb uas muaj peev xwm tiv taus ntau pua lub voj voog hauv kev siv tsheb. Lub roj teeb zoo tshaj plaws yog qhov tshwm sim ntawm kev sib haum xeeb.