Batirin lithium zai ci karo da yanayi daban-daban yayin amfani da su. A cikin hunturu, yawan zafin jiki a arewacin kasar Sin yana ƙasa da 0 ℃ ko ma -10 ℃. Lokacin da aka saukar da caji da cajin baturi ƙasa da 0℃, ƙarfin caji da caji da ƙarfin lantarki na baturin lithium zai ragu sosai. Wannan saboda motsi na lithium ions a cikin electrolyte, SEI da graphite barbashi an rage su a ƙananan zafin jiki. Irin wannan mummunan yanayin ƙarancin zafin jiki ba makawa zai haifar da hazo na ƙarfe na lithium tare da takamaiman yanki na musamman.

Hazowar lithium tare da takamaiman yanki na musamman yana ɗaya daga cikin mahimman dalilai na gazawar tsarin batirin lithium, da kuma matsala mai mahimmanci don amincin baturi. Wannan shi ne saboda yana da babban yanki mai girman gaske, ƙarfe na lithium yana aiki sosai kuma yana ƙonewa, babban filin dendrite lithium yana da ɗan rigar iska za a iya kona.

Tare da haɓaka ƙarfin baturi, kewayon da kasuwar kasuwar motocin lantarki, bukatun aminci na motocin lantarki suna ƙara ƙarfi. Menene canje-canje a aikin batura masu ƙarfi a ƙananan zafin jiki? Wadanne fannonin tsaro ya kamata a lura dasu?

1.18650 gwajin sake zagayowar cryogenic da nazarin rarrabuwar batir

Batirin 18650 (2.2A, NCM523/ graphite tsarin) an kwaikwayi shi a ƙananan zafin jiki na 0℃ ƙarƙashin wani takamaiman tsarin cajin caji. Na’urar caji da caji ita ce: cajin CC-CV, cajin kuɗi shine 1C, cajin yanke wuta shine 4.2V, cajin yankewa shine 0.05c, sannan CC fitarwa zuwa 2.75V. Kamar yadda batirin SOH na 70% -80% gabaɗaya ke bayyana azaman yanayin ƙarewa (EOL) na baturi. Saboda haka, a cikin wannan gwaji, baturin yana ƙare lokacin da SOH na baturin ya kasance 70%. Ana nuna madauwari ta sake zagayowar baturin ƙarƙashin sharuɗɗan da ke sama a cikin hoto 1 (a). An gudanar da bincike na Li MAS NMR akan sanduna da diaphragms na batura masu yawo da maras kewayawa, kuma an nuna sakamakon maye gurbin sinadaran a cikin Hoto 1 (b).

Hoto 1. Hannun sake zagayowar salula da nazarin Li MAS NMR

Ƙarfin sake zagayowar cryogenic ya karu a cikin ƙananan hawan keke na farko, wanda ya biyo baya ta hanyar raguwa, kuma SOH ya ragu a ƙasa da 70% a cikin ƙasa da 50. Bayan an gama harhada baturin, an gano cewa akwai wani nau’in nau’in nau’i na azurfa-toka-toka a saman na’urar, wanda aka dauka karfen lithium ne da aka ajiye a saman kayan anode da ke zagayawa. An gudanar da nazarin Li MAS NMR akan batura na ƙungiyoyin kwatancen gwaji guda biyu, kuma an ƙara tabbatar da sakamakon a cikin Hoto B.

Akwai babban kololuwa a 0ppm, yana nuna cewa akwai lithium a cikin SEI a wannan lokacin. Bayan sake zagayowar, kololuwar na biyu ya bayyana a 255 PPM, wanda zai iya samuwa ta hanyar hazo na ƙarfe na lithium a saman kayan anode. Don ƙara tabbatar da ko lithium dendrites ya bayyana da gaske, an lura da ilimin halittar jiki na SEM, kuma an nuna sakamakon a cikin Hoto 2.

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Hoto 2. Sakamakon bincike na SEM

Ta hanyar kwatanta hotuna A da B, za a iya ganin cewa wani kauri mai kauri ya ɓullo a cikin hoton B, amma wannan Layer bai cika ɓoyayyiyar graphite gaba ɗaya ba. An ƙara haɓaka girman SEM kuma an lura da allura kamar kayan abu a cikin Hoto D, wanda zai iya zama lithium tare da babban yanki na musamman (wanda aka sani da dendrite lithium). Bugu da ƙari, jigon ƙarfe na lithium yana girma zuwa diaphragm, kuma ana iya lura da kauri ta hanyar kwatanta shi da kauri na graphite Layer.

Siffar lithium da aka ajiye ya dogara da abubuwa da yawa. Irin su rashin ƙarfi na ƙasa, ƙarancin halin yanzu, matsayi na caji, zafin jiki, ƙari na electrolyte, abun da ke ciki na lantarki, ƙarfin lantarki da sauransu. Daga cikin su, ƙananan wurare dabam dabam da zafin jiki mai girma a halin yanzu sune mafi sauƙi don samar da ƙananan ƙarfe na lithium tare da babban yanki na musamman.

2. Thermal kwanciyar hankali bincike na baturi lantarki

Anyi amfani da TGA don tantance na’urorin batir da ba a zagaya ba da kuma bayan da aka zagaya, kamar yadda aka nuna a hoto na 3.

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Hoto 3. TGA bincike na korau da m lantarki (A. Negative electrode B. Positive electrode)

Kamar yadda ake iya gani daga adadi a sama, da mara amfani da lantarki da uku muhimmanci kololuwa a T≈260 ℃, 450 ℃ da 725 ℃ bi da bi, yana nuna cewa tashin hankali bazuwa, evaporation ko sublimation halayen faruwa a wadannan wurare. Duk da haka, da taro asarar da lantarki ya bayyana a 33 ℃ da 200 ℃. Halin lalacewa a cikin ƙananan zafin jiki yana haifar da lalacewa na SEI membrane, ba shakka, yana da alaƙa da abun da ke cikin electrolyte da sauran dalilai. Hazo na karfen lithium tare da babban yanki na musamman yana haifar da samar da adadi mai yawa na fina-finai na SEI akan saman karfen lithium, wanda kuma shine dalilin asarar yawan batura a ƙarƙashin yanayin ƙarancin zafin jiki.

SEM ba zai iya ganin wani canje-canje a cikin ilimin halittar jiki na kayan cathode ba bayan gwajin gwaji na cyclic, kuma bincike na TGA ya nuna cewa an sami asarar inganci mai kyau lokacin da zafin jiki ya kasance sama da 400 ℃. Wannan hasara mai yawa na iya haifar da raguwar lithium a cikin kayan cathode. Kamar yadda aka nuna a hoto na 3 (b), tare da tsufa na baturi, abun ciki na Li a cikin ingantaccen lantarki na NCM yana raguwa a hankali. Babban hasara na SOH100% tabbataccen lantarki shine 4.2%, kuma na SOH70% tabbataccen lantarki shine 5.9%. A cikin wata kalma, yawan asarar asarar duka biyu masu inganci da mara kyau suna ƙaruwa bayan sake zagayowar cryogenic.

3. Electrochemical tsufa bincike na electrolyte

GC/MS ne yayi nazarin tasirin ƙarancin zafin jiki akan batir electrolyte. An ɗauki samfuran lantarki daga batura marasa tsufa da kuma waɗanda suka tsufa bi da bi, kuma an nuna sakamakon binciken GC/MS a hoto na 4.

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Hoto 4.GC/MS da sakamakon gwajin FD-MS

Electrolyte na baturin sake zagayowar ba-cryogenic ya ƙunshi DMC, EC, PC, da FEC, PS, da SN azaman abubuwan haɗawa don inganta aikin baturi. Adadin DMC, EC da PC a cikin tantanin halitta da ba a zazzagewa ba da kuma tantanin halitta iri ɗaya ne, kuma ƙari SN a cikin electrolyte bayan zagayawa (wanda ke hana bazuwar tabbataccen electrolytic ruwa oxygen a ƙarƙashin babban ƙarfin lantarki) yana raguwa. , don haka dalili shi ne cewa tabbataccen na’urar lantarki yana da cajin wani sashi a ƙarƙashin ƙananan yanayin zafi. BS da FEC sune abubuwan haɓaka fina-finai na SEI, waɗanda ke haɓaka ƙirƙirar fina-finai na SEI. Bugu da ƙari, FEC na iya inganta kwanciyar hankali na sake zagayowar da ingancin Coulomb na batura. PS na iya haɓaka kwanciyar hankali na thermal na anode SEI. Kamar yadda ake iya gani daga adadi, adadin PS baya raguwa tare da tsufa na baturi. An sami raguwa sosai a cikin adadin FEC, kuma lokacin da SOH ya kasance 70%, FEC ba a iya gani ba. Bacewar FEC yana faruwa ne ta hanyar ci gaba da sake gina SEI, kuma sake gina SEI na sake ginawa yana faruwa ne ta hanyar ci gaba da hazo na Li a saman cathode graphite.

Babban samfurin electrolyte bayan sake zagayowar baturi shine DMDOHC, wanda tsarinsa yayi daidai da samuwar SEI. Saboda haka, babban adadin DMDOHC a cikin FIG. 4A yana nuna samuwar manyan wuraren SEI.

4. Thermal kwanciyar hankali bincike na ba-cryogenic baturi sake zagayowar

An gudanar da gwaje-gwajen ARC (Accelerated calorimeter) akan sake zagayowar mara amfani da batura na sake zagayowar cryogenic a ƙarƙashin yanayin quasi-adiabatic da yanayin HWS. Sakamakon Arc-hws ya nuna cewa abin da ke cikin baturi ne ya haifar da tashin hankali, wanda ba shi da yanayin zafi na waje. Halin da ke cikin baturin za a iya raba shi zuwa matakai uku, kamar yadda aka nuna a Table 1.

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Ƙunƙarar ɓangarori na zafi yana faruwa a lokacin diaphragm thermalization da fashewar baturi, amma diaphragm thermalization ne sakaci ga dukan SHR. Halin farko na exothermic ya fito ne daga bazuwar SEI, biye da induction na thermal don haifar da ƙaddamar da ions lithium, isowar electrons zuwa saman graphite, da kuma rage electrons don sake kafa membrane na SEI. Ana nuna sakamakon gwajin kwanciyar hankali na thermal a hoto na 5.

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Hoto 5. Sakamakon Arc-hws (a) 0% SOC; (b) 50 bisa dari SOC; (c) 100 bisa dari SOC; Layukan da aka tsinke sune zafin zafin farko na exothermic, zafin runaway na farko na thermal da zafin gudu na thermal.

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Hoto 6. Tafsirin sakamakon Arc-hws a. Zazzabi na gudu na thermal, farawa B.ID, C. Farkon zafin jiki na thermal runaway d. Zazzabi na farko na halayen exothermic

Halin farko na exothermic (OER) na baturi ba tare da sake zagayowar cryogenic yana farawa a kusa da 90 ℃ kuma yana ƙaruwa kai tsaye zuwa 125 ℃, tare da raguwar SOC, yana nuna cewa OER ya dogara sosai akan yanayin lithium ion a cikin anode. Domin baturi a cikin fitarwa tsari, SHR mafi girma (kai dumama kudi) a cikin bazuwar dauki ne generated a game da 160 ℃, da kuma SHR zai rage a high zafin jiki, don haka da amfani da intercalated lithium ions aka ƙaddara a korau electrode. .

Muddin akwai isassun ions lithium a cikin gurɓataccen lantarki, an tabbatar da cewa za a iya sake gina SEI mai lalacewa. Rushewar thermal na kayan cathode zai saki iskar oxygen, wanda zai oxidize tare da electrolyte, a ƙarshe yana haifar da halayen zafin zafi na baturi. A karkashin babban SOC, kayan cathode yana cikin yanayin delithium sosai, kuma tsarin kayan cathode kuma shine mafi rashin kwanciyar hankali. Abin da ke faruwa shi ne cewa kwanciyar hankali na thermal na tantanin halitta yana raguwa, adadin iskar oxygen da aka saki yana ƙaruwa, kuma amsawa tsakanin tabbataccen lantarki da electrolyte yana ɗauka a yanayin zafi.

4. Sakin makamashi yayin samar da iskar gas

Ta hanyar nazarin baturin bayan sake zagayowar, ana iya ganin cewa SHR ya fara girma a cikin madaidaiciyar layi a kusa da 32 ℃. Sakin makamashi a cikin tsarin samar da iskar gas yana faruwa ne ta hanyar rarrabuwar yanayi, wanda gabaɗaya ana ɗauka shine bazuwar thermal na electrolyte.

Karfe na lithium tare da takamaiman yanki na musamman yana hazo a saman kayan anode, wanda za’a iya bayyana shi ta wannan ma’auni.

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A cikin tallatawa, Cp shine takamaiman ƙarfin zafi, kuma △T yana wakiltar jimlar zafin zafin baturi wanda ya haifar da yanayin ruɓewa a gwajin ARC.

An gwada takamaiman ƙarfin zafi na ƙwayoyin da ba a kewaya tsakanin 30 ℃ da 120 ℃ a cikin gwaje-gwajen ARC. A exothermic dauki faruwa a 125 ℃, kuma baturi ne a cikin fitarwa jihar, kuma babu wani exothermic dauki tsoma baki tare da shi. A cikin wannan gwaji, CP yana da alaƙa ta layi tare da zafin jiki, kamar yadda aka nuna a cikin ma’auni mai zuwa.

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Jimlar adadin kuzarin da aka fitar a cikin duka halayen ana iya samun su ta hanyar haɗa takamaiman ƙarfin zafi, wanda shine 3.3Kj kowane tsufa tantanin halitta a ƙananan yanayin zafi. Ba za a iya ƙididdige adadin kuzarin da aka fitar yayin guduwar zafi ba.

5. Gwajin Acupuncture

Don tabbatar da tasirin tsufa na baturi akan gwajin gajeriyar kewaya batir, an gudanar da gwajin allura. Ana nuna sakamakon gwaji a cikin hoton da ke ƙasa:

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Dangane da sakamakon acupuncture, A shine yanayin yanayin baturi yayin aikin acupuncture, kuma B shine matsakaicin zafin jiki wanda za’a iya samu.

Ana iya gani daga adadi cewa akwai ɗan bambanci kaɗan na 10-20 ℃ tsakanin batirin tsufa bayan fitarwa da sabon baturi (SOC 0%) ta hanyar buƙatar gwaji. Ga tsofaffin tantanin halitta, cikakken zafin jiki ya kai T≈35 ℃ a ƙarƙashin yanayin adiabatic, wanda yayi daidai da SHR≈0.04K/min.

Batirin da ba a yi amfani da shi ya kai matsakaicin zafin jiki na 120 ℃ bayan daƙiƙa 30 lokacin da SOC ke 50%. Zafin joule da aka saki bai isa ya kai wannan zafin ba, kuma SHR ya wuce adadin yaduwar zafi. Lokacin da SOC ya kasance 50%, baturin tsufa yana da wani tasiri na jinkiri akan guduwar zafi, kuma zafin jiki yana tashi sosai zuwa 135 ℃ lokacin da aka saka allura a cikin baturi. Sama da 135 ℃, haɓakar SHR yana haifar da guduwar baturi, kuma yanayin zafin baturin ya tashi zuwa 400 ℃.

An ga wani al’amari na daban lokacin da sabon baturi ya cika da tsinken allura. Wasu sel sun rasa kulawar thermal kai tsaye, yayin da wasu ba su rasa kulawar thermal lokacin da yanayin zafin jiki ya kasance ƙasa da 125 ℃. Daya daga cikin wutar lantarki kai tsaye da ke sarrafa batirin bayan allurar ta shiga cikin batirin, yanayin zafin saman ya kai 700 ℃, wanda hakan ya sa foil din aluminum ya narke, bayan wasu dakika kadan, sandar ta narke aka raba shi da baturin, sannan ya kunna wuta. na iskar gas, kuma a ƙarshe ya haifar da dukan harsashi ja. Ƙungiyoyin biyu na abubuwan mamaki daban-daban za a iya ɗauka su zama cewa diaphragm yana narkewa a 135 ℃. Lokacin da zafin jiki ya fi 135 ℃, diaphragm yana narkewa kuma gajeriyar da’ira ta ciki ta bayyana, yana haifar da ƙarin zafi kuma a ƙarshe yana haifar da guduwar thermal. Don tabbatar da wannan, an tarwatsa baturin gudu mara zafi kuma an gwada diaphragm AFM. Sakamakon ya nuna cewa farkon yanayin narkewar membrane ya bayyana a ɓangarorin biyu na membrane, amma tsarin porous har yanzu ya bayyana akan mummunan gefe, amma ba a gefen tabbatacce ba.