Rationally designing electrolyte additives for highly improving cyclability of LiNi_(0.5)Mn_(1.5)O_(4)/Graphite cells

High voltage is necessary for high energy lithium-ion batteries but difficult to achieve because of the highly deteriorated cyclability of the batteries.A novel strategy is developed to extend cyclability of a high voltage lithium-ion battery,LiNi_(0.5)Mn_(1.5)O_(4)/Graphite(LNMO/Graphite)cell,which emphasizes a rational design of an electrolyte additive that can effectively construct protective interphases on anode and cathode and highly eliminate the effect of hydrogen fluoride(HF).5-Trifluoromethylpyridine-trime thyl lithium borate(LTFMP-TMB),is synthesized,featuring with multi-functionalities.Its anion TFMPTMB-tends to be enriched on cathode and can be preferentially oxidized yielding TMB and radical TFMP-.Both TMB and radical TFMP can combine HF and thus eliminate the detrimental effect of HF on cathode,while the TMB dragged on cathode thus takes a preferential oxidation and constructs a protective cathode interphase.On the other hand,LTFMP-TMB is preferentially reduced on anode and constructs a protective anode interphase.Consequently,a small amount of LTFMP-TMB(0.2%)in 1.0 M LiPF6in EC/DEC/EMC(3/2/5,wt%)results in a highly improved cyclability of LNMO/Graphite cell,with the capacity retention enhanced from 52%to 80%after 150 cycles at 0.5 C between 3.5 and 4.8 V.The as-developed strategy provides a model of designing electrolyte additives for improving cyclability of high voltage batteries.

Tackling application limitations of high-safetyγ-butyrolactone electrolytes:Exploring mechanisms and proposing solutions

Developing wide-temperature and high-safety lithium-ion batteries(LIBs)presents significant challenges attributed to the absence of suitable solvents possessing broad liquid range and non-flammability properties.γ-Butyrolactone(GBL)has emerged as a promising solvent;however,its incompatibility with graphite anode has hindered its application.This limitation necessitates a comprehensive investigation into the underlying mechanisms and potential solutions.In this study,we achieve a molecular-level understanding of the perplexing interphase formation process by employing in-situ spectroelectrochemical techniques and density function calculations.Our findings reveal that,even at high salt concentrations,GBL consistently occupies the primary Li^(+)solvation sheath,leading to extensive GBL decomposition and the formation of a high-impedance and inorganic-poor solid-electrolyte interphase(SEI)layer.Contrary to manipulating solvation structures,our research demonstrates that the utilization of filmforming additives with higher reduction potential facilitates the pre-establishment of a robust SEI film on the graphite anode.This approach effectively inhibits GBL decomposition and significantly enhances the battery's lifespan.This study provides the first reported intrinsic understanding of the unique GBLgraphite incompatibility and offers valuable insights for the development of wide-temperature and high-safety LIBs.

Outstanding performances of graphite||NMC622 pouch cells enabled by a non-inert diluent

Although high salt concentration electrolyte(HCE)can construct effective Li F-rich interphase film and solve the interphasial instability issue of graphite anode,its high cost,high viscosity and poor wettability with electrode materials limit its large-scale application.Generally,localized high concentration electrolyte(LHCE)is obtained by introducing an electrochemically inert diluent into HCE to avoid the above-mentioned problems while maintaining the high interphasial stability of HCE with graphite anode.Unlike traditional inert diluents,1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluropropyl ether(TTE)with electrochemical activity is introduced into propylene carbonate(PC)-based HCE to obtain LHCE-2(1 M LiPF_(6),PC:DMC:TTE=1:1:6.1)herein.Experimental and theoretical simulation results show that TTE participates in the oxidation decomposition and film-forming reaction at the NCM622 cathode surface,conducting a cathode electrolyte interphase(CEI)rich in organic fluorides with excellent electron insulation ability,high structural stability and low interphasial impedance.Thanks to the outstanding interphasial properties induced by LHCE-2,the graphite||NMC622 pouch cell reaches a capacity retention of 80%after 500 cycles at 1 C under room temperature.While at sub-zero temperatures,the capacity released by the cell with LHCE-2 electrolyte is significantly higher than that of HCE and conventional EC-based electrolytes.Meanwhile,the LHCE-2 electrolyte inherits the advantages of TTE flame-resistant,thus improving the safety of the battery.

Synergistic interphase modification with dual electrolyte additives to boost cycle stability of high nickel cathode for all-climate battery

B-containing electrolyte additives are widely used to enhance the cycle performance at low temperature and the rate capability of lithium-ion batteries by constructing an efficient cathode electrolyte interphase(CEI)to facilitate the rapid Li+migration.Nevertheless,its wide-temperature application has been limited by the instability of B-derived CEI layer at high temperature.Herein,dual electrolyte additives,consisting of lithium tetraborate(Li_(2)TB)and 2,4-difluorobiphenyl(FBP),are proposed to boost the widetemperature performances of LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)(NCM)cathode.Theoretical calculation and electrochemical performances analyses indicate that Li_(2)TB and FBP undergo successive decomposition to form a unique dual-layer CEI.FBP acts as a synergistic filming additive to Li_(2)TB,enhancing the hightemperature performance of NCM cathode while preserving the excellent low-temperature cycle stability and the superior rate capability conferred by Li_(2)TB additive.Therefore,the capacity retention of NCM‖Li cells using optimal FBP-Li_(2)TB dual electrolyte additives increases to 100%after 200 cycles at-10℃,99%after 200 cycles at 25℃,and 83%after 100 cycles at 55℃,respectively,much superior to that of base electrolyte(63%/69%/45%).More surprisingly,galvanostatic c ha rge/discharge experiments at different temperatures reveal that NCM‖Li cells using FBP-Li_(2)TB additives can operate at temperatures ranging from-40℃to 60℃.This synergistic interphase modification utilizing dual electrolyte additives to construct a unique dual-layer CEI adaptive to a wide temperature range,provides valuable insights to the practical applications of NCM cathodes for all-climate batteries.

Innovative discontinuous-SEI constructed in ether-based electrolyte to maximize the capacity of hard carbon anode

Compared with graphite,the lower sodiation potential and larger discharge capacity of hard carbon(HC)makes it the most promising anode material for sodium-ion battery.Utilizing ether-based electrolyte rather than conventional carbonate-based electrolyte,HC achieves superior electrochemical performance.Nevertheless,the mechanism by which ether-based electrolyte improves the properties of HC is still controversial,primarily focusing on whether it forms solid electrolyte interphase(SEI)film.In this work,according to the sodium storage mechanisms in HC at low voltage(<0.1 V),including Na^(+)-diglyme co-interaction into the carbon layer(SEI forbidden)and desolvated Na^(+)insertion in the irregular carbon holes(SEI required),the NaPF6concentration in ether-based electrolyte was regulated,so as to construct a discontinuous-SEI on the surface of the HC anode,which significantly enhances the electrochemical performances of HC.Specifically,with 0.2 M NaPF6ether-based electrolyte,HC deliverers a discharge capacity of 459.7 mA h g^(-1)at 0.1 C and stays at 357.2 mA h g^(-1)after 500 cycles at 1 C,which is substantially higher than that of higher/lower salt concentration electrolytes.