Batirin lithium-ion sune baturan sakandare mafi girma da sauri bayan nickel-cadmium da nickel-hydrogen baturi. Abubuwan da ke da ƙarfin kuzari suna sa makomarta ta yi haske. Duk da haka, batir lithium-ion ba cikakke ba ne, kuma babbar matsalar su ita ce kwanciyar hankali na hawan cajin su. Wannan takarda ta taƙaita tare da yin nazarin dalilan da za su iya haifar da faɗuwar ƙarfin batir Li-ion, gami da cajin da ya wuce kima, lalatawar lantarki da fitar da kai.

Batirin lithium-ion suna da kuzarin haɗakarwa daban-daban lokacin da halayen tsaka-tsakin ke faruwa tsakanin na’urorin lantarki guda biyu, kuma don samun mafi kyawun aikin baturi, ƙimar ƙarfin na’urorin lantarki guda biyu yakamata su kula da daidaiton ƙima.

A cikin batirin lithium-ion, ana bayyana ma’aunin iya aiki azaman yawan adadin ma’aunin ma’auni mai kyau zuwa na’urar lantarki mara kyau,

Wato: γ=m+/m-=ΔxC-/ΔyC+

In the above formula, C refers to the theoretical coulombic capacity of the electrode, and Δx and Δy refer to the stoichiometric number of lithium ions embedded in the negative electrode and the positive electrode, respectively. It can be seen from the above formula that the required mass ratio of the two poles depends on the corresponding Coulomb capacity of the two poles and the number of their respective reversible lithium ions.

hoto

Gabaɗaya magana, ƙaramin adadin taro yana kaiwa ga rashin cika amfani da kayan lantarki mara kyau; babban rabo mai girma na iya haifar da haɗari na aminci saboda yawan cajin da aka yi masa mara kyau. A takaice, a ingantacciyar rabon taro, aikin baturi shine mafi kyau.

Don tsarin baturi mai mahimmanci na Li-ion, ma’auni na iya aiki ba ya canzawa yayin zagayowar sa, kuma ƙarfin farko a cikin kowane zagayowar yana da ƙima, amma ainihin halin da ake ciki ya fi rikitarwa. Duk wani martani na gefe wanda zai iya haifar ko cinye lithium ions ko electrons na iya haifar da canje-canje a ma’aunin ƙarfin baturi. Da zarar yanayin ma’aunin ƙarfin baturi ya canza, wannan canjin ba zai iya jurewa ba kuma ana iya tara shi ta kewayawa da yawa, yana haifar da aikin baturi. Mummunan tasiri. A cikin baturan lithium-ion, baya ga redox halayen da ke faruwa a lokacin da lithium ions ke raguwa, akwai kuma adadi mai yawa na halayen gefe, irin su bazuwar electrolyte, rushewar kayan aiki, da ƙaddamar da lithium na ƙarfe.

Reason 1: Overcharging

1. Overcharge dauki na graphite korau electrode:

Lokacin da baturi ya yi yawa, ions lithium ana rage su cikin sauƙi kuma a ajiye su a saman ƙarancin lantarki:

hoto

The deposited lithium coats the negative electrode surface, blocking the intercalation of lithium. This results in reduced discharge efficiency and capacity loss due to:

①Rage adadin lithium mai sake yin fa’ida;

②The ajiya karfe lithium reacts tare da sauran ƙarfi ko goyon bayan electrolyte don samar da Li2CO3, LiF ko wasu kayayyakin;

③ Metal lithium yawanci ana samuwa ne tsakanin gurɓataccen lantarki da mai rarrabawa, wanda zai iya toshe pores na mai raba kuma ƙara juriya na ciki na baturi;

④ Saboda yanayin aiki mai mahimmanci na lithium, yana da sauƙi don amsawa tare da masu amfani da wutar lantarki da cinye wutar lantarki, yana haifar da raguwa a cikin fitarwa da kuma asarar iya aiki.

Yin caji da sauri, yawan adadin yanzu yana da girma, ƙarancin wutar lantarki yana da ƙarfi sosai, kuma shigar da lithium zai fi fitowa fili. Wannan yana yiwuwa ya faru lokacin da ingantaccen kayan aiki na lantarki ya wuce gona da iri zuwa kayan aiki mara kyau. Koyaya, a cikin yanayin ƙimar caji mai girma, ƙaddamar da lithium na ƙarfe na iya faruwa ko da rabon kayan aiki masu inganci da mara kyau na al’ada ne.

2. Kyakkyawan amsawar cajin wutar lantarki

When the ratio of positive electrode active material to negative electrode active material is too low, positive electrode overcharge is likely to occur.

Asarar ƙarfin aiki da ke haifar da ƙarin cajin ingantacciyar wutar lantarki ya samo asali ne saboda haɓakar abubuwan da ba a iya amfani da su ba (irin su Co3O4, Mn2O3, da sauransu), waɗanda ke lalata ma’aunin ƙarfin aiki tsakanin na’urorin lantarki, kuma asarar ƙarfin ba za ta iya jurewa ba.

(1) LiyCoO2

LiyCoO2→(1-y)/3[Co3O4＋O2(g)]＋yLiCoO2 y<0.4

A lokaci guda kuma, iskar oxygen da ke haifarwa ta hanyar rugujewar ingantaccen kayan lantarki a cikin baturin lithium-ion da aka rufe yana taruwa a lokaci guda saboda babu wani abu na sake haduwa (kamar halittar H2O) da iskar gas mai ƙonewa da ruɗuwar ta haifar. na electrolyte, kuma sakamakon zai zama wanda ba za a iya misaltuwa ba.

(2) λ-MnO2

Halin lithium-manganese yana faruwa lokacin da lithium-manganese oxide ya lalace gaba ɗaya: λ-MnO2→Mn2O3+O2(g)

3. Electrolyte yana oxidized lokacin da aka cika caji

Lokacin da matsa lamba ya fi 4.5V, electrolyte zai zama oxidized don samar da insoluble (irin su Li2Co3) da gas. Wadannan insolubles za su toshe micropores na lantarki da kuma hana ƙaura na lithium ions, haifar da asarar iya aiki yayin hawan keke.

Abubuwan da ke shafar ƙimar oxidation:

The surface area of ​​the positive electrode material

Abubuwan tarawa na yanzu

Added conductive wakili (carbon black, da dai sauransu)

The type and surface area of ​​carbon black

Daga cikin mafi yawan amfani da electrolytes, EC/DMC ana ɗauka yana da mafi girman juriya na iskar shaka. A electrochemical hadawan abu da iskar shaka tsari na bayani ne gaba ɗaya bayyana a matsayin: bayani →oxidation samfurin (gas, bayani da kuma m al’amari)+ ne-

The oxidation of any solvent will increase the electrolyte concentration, decrease the electrolyte stability, and ultimately affect the capacity of the battery. Assuming that a small amount of electrolyte is consumed each time it is charged, more electrolyte is required during battery assembly. For a constant container, this means that a smaller amount of active substance is loaded, which results in a decrease in the initial capacity. In addition, if a solid product is produced, a passivation film will be formed on the surface of the electrode, which will increase the polarization of the battery and reduce the output voltage of the battery.

Dalili 2: Electrolyte bazuwar (raguwa)

Ina bazuwa akan lantarki

1. Electrolyte ya lalace akan ingantaccen lantarki:

Electrolyte ya ƙunshi ƙarfi da lantarki mai tallafi. Bayan cathode ya lalace, samfuran da ba za su iya narkewa kamar Li2Co3 da LiF galibi ana yin su, waɗanda ke rage ƙarfin baturi ta hanyar toshe ramukan lantarki. Halin raguwar electrolyte zai yi mummunan tasiri akan iya aiki da rayuwar sake zagayowar baturin. Gas ɗin da aka samar ta hanyar raguwa zai iya ƙara ƙarfin ciki na baturi, wanda zai haifar da matsalolin tsaro.

Ingantacciyar wutar lantarki mai lalata wutar lantarki yawanci tana da girma fiye da 4.5V (vs. Li/Li+), don haka ba sa saurin rubewa akan ingantaccen lantarki. Akasin haka, electrolyte ya fi sauƙi bazuwa a mummunan lantarki.

2. Electrolyte yana bazu akan magudanar lantarki:

The electrolyte is not stable on graphite and other lithium-inserted carbon anodes, and it is easy to react to generate irreversible capacity. During the initial charge and discharge, the decomposition of the electrolyte will form a passivation film on the surface of the electrode, and the passivation film can separate the electrolyte from the carbon negative electrode to prevent further decomposition of the electrolyte. Thus, the structural stability of the carbon anode is maintained. Under ideal conditions, the reduction of the electrolyte is limited to the passivation film formation stage, and this process does not occur when the cycle is stable.

Samar da fim ɗin wucewa

Rage yawan salts na electrolyte yana shiga cikin samuwar fim ɗin wucewa, wanda ke da amfani ga daidaitawar fim ɗin wucewa, amma

(1) The insoluble matter produced by the reduction will have an adverse effect on the solvent reduction product;

(2) Matsalolin electrolyte yana raguwa lokacin da aka rage gishiri na electrolyte, wanda a ƙarshe zai haifar da asarar ƙarfin baturi (An rage LiPF6 don samar da LiF, LixPF5-x, PF3O da PF3);

(3) Samar da fim ɗin wucewa yana cinye ions lithium, wanda zai haifar da rashin daidaituwa tsakanin nau’ikan lantarki guda biyu don rage takamaiman ƙarfin baturi duka.

(4) Idan akwai fasa a kan passivation film, sauran ƙarfi kwayoyin iya shiga da kuma thicken da passivation film, wanda ba kawai cinye mafi lithium, amma kuma iya toshe micropores a kan carbon surface, sakamakon da kasawa na lithium da za a saka da kuma. cirewa. , yana haifar da asarar ƙarfin da ba za a iya jurewa ba. Ƙara wasu abubuwan da ba a haɗa su ba zuwa electrolyte, irin su CO2, N2O, CO, SO2, da dai sauransu, na iya hanzarta samuwar fim ɗin wucewa kuma ya hana haɗin haɗin gwiwa da rushewar sauran ƙarfi. Bugu da ƙari na kambi ether Organic additives shima yana da tasiri iri ɗaya. 12 rawanin da 4 ethers sune mafi kyau.

Abubuwan da ke haifar da asarar ƙarfin fim:

(1) The type of carbon used in the process;

(2) Abubuwan da ke tattare da lantarki;

(3) Additives a cikin lantarki ko electrolytes.

Blyr believes that the ion exchange reaction advances from the surface of the active material particle to its core, the new phase formed bury the original active material, and a passive film with low ionic and electronic conductivity is formed on the surface of the particle, so the spinel after storage Greater polarization than before storage.

Zhang ya gano cewa juriya na layin wucewar saman ya karu kuma karfin tsaka-tsakin ya ragu tare da karuwar yawan hawan keke. Yana nuna cewa kauri na Layer passivation yana ƙaruwa tare da adadin hawan keke. Rushewar manganese da rushewar electrolyte suna haifar da samuwar fina-finai na wucewa, kuma yanayin zafi mai zafi ya fi dacewa da ci gaban waɗannan halayen. Wannan zai ƙara juriya na lamba tsakanin barbashi na abu mai aiki da juriya na ƙaura Li+, ta haka yana ƙara haɓakar baturi, caji da caji mara cika, da rage ƙarfin aiki.

II Rage Injin Electrolyte

Electrolyte yakan ƙunshi iskar oxygen, ruwa, carbon dioxide da sauran ƙazanta, kuma halayen redox suna faruwa yayin aikin caji da fitar da baturi.

The reduction mechanism of the electrolyte includes three aspects: solvent reduction, electrolyte reduction and impurity reduction:

1. Rage mai narkewa

The reduction of PC and EC includes one-electron reaction and two-electron reaction process, and the two-electron reaction forms Li2CO3:

Fong et al. believed that during the first discharge process, when the electrode potential was close to 0.8V (vs. Li/Li+), the electrochemical reaction of PC/EC occurred on graphite to generate CH=CHCH3(g)/CH2=CH2( g) and LiCO3(s), leading to irreversible capacity loss on graphite electrodes.

Aurbach et al. An gudanar da bincike mai zurfi kan tsarin ragewa da samfuran electrolytes daban-daban akan na’urorin lantarki na ƙarfe na lithium da carbon-based electrodes, kuma sun gano cewa tsarin amsawar lantarki guda ɗaya na PC yana samar da ROCO2Li da propylene. ROCO2Li yana da matukar damuwa ga gano ruwa. Babban samfurori sune Li2CO3 da propylene a gaban ruwa mai ganowa, amma ba a samar da Li2CO3 a karkashin yanayin bushe ba.

Maido da DEC:

Ein-Eli Y ya ruwaito cewa electrolyte gauraye da diethyl carbonate (DEC) da dimethyl carbonate (DMC) za su fuskanci wani canji a cikin baturi don samar da ethyl methyl carbonate (EMC), wanda ke da alhakin asarar iya aiki. wani tasiri.

2. Ragewar Electrolite

Ana la’akari da raguwar ragi na electrolyte gabaɗaya da hannu a cikin samuwar fim ɗin fili na carbon electrode, don haka nau’in sa da maida hankalinsa zai shafi aikin lantarki na carbon. A wasu lokuta, raguwa na electrolyte yana taimakawa wajen daidaita yanayin sararin samaniya, wanda zai iya samar da Layer passivation da ake so.

It is generally believed that the supporting electrolyte is easier to reduce than the solvent, and the reduction product is mixed in the negative electrode deposition film and affects the capacity decay of the battery. Several possible reduction reactions of supporting electrolytes are as follows:

3. Rage kazanta

(1) Idan abun ciki na ruwa a cikin electrolyte ya yi yawa, LiOH(s) da Li2O za a samar da su, wanda bai dace da shigar da ions lithium ba, yana haifar da asarar ƙarfin da ba za a iya jurewa ba:

H2O＋e→OH-＋1/2H2

OH-＋Li+→LiOH(s)

LiOH+Li++e-→Li2O(s)+1/2H2

The generated LiOH(s) is deposited on the electrode surface, forming a surface film with high resistance, which hinders Li+ intercalation into the graphite electrode, resulting in irreversible capacity loss. A small amount of water (100-300×10-6) in the solvent has no effect on the performance of the graphite electrode.

(2) CO2 a cikin sauran ƙarfi za a iya rage a kan mummunan lantarki don samar da CO da LiCO3(s):

2CO2+2e-+2Li+→Li2CO3+CO

CO zai ƙara matsa lamba na ciki na baturi, kuma Li2CO3(s) zai ƙara ƙarfin ciki na baturin kuma yana rinjayar aikin baturi.

(3) The presence of oxygen in the solvent will also form Li2O

1/2O2+2e-+2Li+→Li2O

Saboda yuwuwar bambance-bambancen da ke tsakanin ƙarfe na ƙarfe na ƙarfe na ƙarfe da keɓaɓɓen carbon da ke tsaka-tsaki kaɗan ne, raguwar electrolyte akan carbon yayi kama da raguwar lithium.

Dalili na uku: Fitar da kai

Fitar da kai yana nufin lamarin da baturi ke rasa ƙarfinsa a zahiri lokacin da ba a amfani da shi. Fitar da kan batirin Li-ion yana haifar da asarar iya aiki a lokuta biyu:

Daya shine asarar iya aiki mai juyawa;

Na biyu shine asarar ƙarfin da ba za a iya jurewa ba.

Asarar iya jujjuyawa yana nufin cewa za a iya dawo da ƙarfin da aka rasa yayin caji, yayin da asarar ƙarfin da ba za a iya jurewa ba shine akasin haka. Na’urorin lantarki masu inganci da marasa kyau na iya yin aiki azaman microbattery tare da electrolyte a cikin halin da ake cajin, wanda ya haifar da haɗin gwiwar lithium ion intercalation da deintercalation, da haɓakawa da ƙaddamar da ƙwayoyin lantarki masu inganci da korau. Abubuwan ions lithium da aka haɗa suna da alaƙa kawai da ions lithium na electrolyte, don haka ƙarfin madaidaicin ma’auni da mara kyau ba shi da daidaituwa, kuma wannan ɓangaren asarar ƙarfin ba za a iya dawo da shi yayin caji ba. Kamar:

Lithium manganese oxide tabbatacce electrode da sauran ƙarfi zai haifar da tasirin micro-batir da fitar da kai, yana haifar da asarar ƙarfin da ba za a iya jurewa ba:

LiyMn2O4+xLi++xe-→Liy+xMn2O4

Solvent molecules (such as PC) are oxidized on the surface of conductive material carbon black or current collector as a microbattery anode:

xPC→xPC-radical+xe-

Similarly, the negative active material may interact with the electrolyte to cause self-discharge and cause irreversible capacity loss, and the electrolyte (such as LiPF6) is reduced on the conductive material:

PF5+xe-→PF5-x

Lithium carbide a cikin halin da ake caji yana da iskar oxygen ta hanyar cire ions lithium azaman mummunan lantarki na microbattery:

LiyC6→Liy-xC6+xLi++++xe-

Abubuwan da ke shafar fitar da kai: tsarin masana’anta na ingantaccen kayan lantarki, tsarin masana’anta na baturi, kaddarorin electrolyte, zazzabi, da lokaci.