Novel polyimide binder for achieving high-rate capability and long-term cycling stability of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) cathode via constructing polar and micro-branched crosslinking network structure

LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)material,as the promising cathode candidate for next-generation highenergy lithium-ion batteries,has gained considerable attention for extremely high theoretical capacity and low cost.Nevertheless,the intrinsic drawbacks of NCM811 such as unstable structure and inevitable interface side reaction result in severe capacity decay and thermal runaway.Herein,a novel polyimide(denoted as PI-Om DT)constructed with the highly polar and micro-branched crosslinking network is reported as a binder material for NCM811 cathode.The micro-branched crosslinking network is achieved by using 1,3,5-Tris(4-aminophenoxy)benzene(TAPOB)as a crosslinker via condensation reaction,which endows excellent mechanical properties and large free volume.Meanwhile,the massive polar carboxyl(-COOH)groups provide strong adhesion sites to active NCM811 particles.These functions of PIOm DT binder collaboratively benefit to forming the mechanically robust and homogeneous coating layer with rapid Li+diffusion on the surface of NCM811,significantly stabilizing the cathode structure,suppressing the detrimental interface side reaction and guaranteeing the shorter ion-diffusion and electron-transfer paths,consequently enhancing electrochemical performance.As compared to the NCM811 with PVDF binder,the NCM811 using PI-Om DT binder delivers a superior high-rate capacity(121.07 vs.145.38 m Ah g^(-1))at 5 C rate and maintains a higher capacity retention(80.38%vs.91.6%)after100 cycles at 2.5–4.3 V.Particularly,at the high-voltage conditions up to 4.5 and 4.7 V,the NCM811 with PI-Om DT binder still maintains the remarkable capacity retention of 88.86%and 72.5%after 100 cycles,respectively,paving the way for addressing the high-voltage operating stability of the NCM811 cathode.Moreover,the full-charged NCM811 cathode with PI-Om DT binder exhibits a significantly enhanced thermal stability,improving the safety performance of batteries.This work opens a new avenue for developing high-energy NCM811 based lithium-ion batteries with long cycle-life and superior safety performance using a novel and effective binder.

Insight into the Electrochemical Behaviors of NCM811|SiO-Gr Pouch Battery through Thickness Variation

LiNi0.8Co0.1Mn0.1O2(NCM811)|SiOx-graphite(SiO-Gr.)battery chemistry is of intensive attention because its achievable practical energy density is approaching impressively 300 Wh Kg^(-1).However,it still suffers rapid capacity fades during repeated cycles,both chemical,electrochemical and mechanical irreversibility contribute.A comprehensive understanding behind the fading behavior of the cell chemistry is required before fully realize the benefits of this chemistry.Herein,the in-situ thickness variation is introduced as a diagnostic technique and is performed on 5-55 Ah NCM811|SiO-Gr cells.With the help of Li reference electrode and in-situ X-ray diffraction device,the correspondence between thickness variation and the electrode potential is carefully investigated.Firstly,the NCM811|SiO-Gr cell is characterized with the maximum cell thickness at around 80%state-of-charge(SOC)in the discharge process,rather than at 100%SOC.Secondly,the electrochemical behaviors during rate charge/discharge are diagnosed,and a Li platting signal is resolved from thickness variation profile at 2C.This work confirms that the thickness monitoring is a nondestructive and informative complement to conventional diagnostic techniques for failure analysis of pouch cells.

Impact of evolution of cathode electrolyte interface of Li(Ni0.8Co0.1Mn0.1)O2 on electrochemical performance during high voltage cycling process

In this work, the electrochemical performance of LiNi0.8Co0.1Mn0.1O2(NCM811) has been investigated after cycling with various upper cutoff voltages. Noteworthily, electrochemical impedance of NCM811 declined with the increasing cycle number to high voltages. It was found that the decline of charge transfer impedance could be related to the structural and compositional change of cathode electrolyte interphase(CEI) of NCM811 when charging to high voltages, based on the characterization of electrochemical impedance spectroscopy(EIS), X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM). The corresponding mechanism has also been proposed in this study. Specifically, due to the increasing roughness of cathode surface, the bottom of CEI film and cubic phase on cathode surface form a transition region mainly at high voltages, leading to the nonobvious boundary. This newly formed transition region at high voltages could promote the Li ion diffusion from electrolyte to cathode, then reducing charge transfer impedance. Additionally, the decrease of Li F on the surface of the cathode could also make a contribution to lower the interface impedance. This study delivers a different evolution of CEI on NCM811, and the impact of CEI evolution on electrochemical performance when charging to a high voltage.

Electrolyte perspective on stabilizing LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)cathode for lithium-ion batteries

Nickel-rich LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)is regarded as the promising cathode for lithium-ion batteries(LIBs).However,the challenges such as safety issues and poor cycling performance have seriously hindered its commercial applications.In order to overcome these difficulties,there has been extensive research and development of electrolyte modifications for high-energy-density LIBs with Ni-rich cathodes.Herein,this review introduces the research progress based on solvent additives,salt type additives and other electrolytes for LIBs with NCM811cathode materials and discusses how they control the interface stability.In particular,some recommendations for further modification of enhancing electrolyte stability and improving NCM811 electrochemical properties are summarized and proposed,which put forward new design rules for the screening and customizing ideal electrolyte additives for high performance NCM811 cathode-based LIBs.

Understanding and quantifying capacity loss in storage aging of Ah-level Li metal pouch cells

Promoting industry applications of high-energy Li metal batteries(LMBs)is of vital importance for accelerating the electrification and decarbonization of our society.Unfortunately,the time-dependent storage aging of Ah-level Li metal pouch cells,a ubiquitous but crucial practical indicator,has not yet been revealed.Herein,we first report the storage behaviors and multilateral synergistic aging mechanism of Ah-level NCM811jjLi pouch cells during the 120-day long-term storage under various conditions.Contrary to the conventional belief of Li-ion batteries with graphite intercalation anodes,the significant available capacity loss of 32.8%on average originates from the major electrolyte-sensitive anode corrosion and partial superimposed cathode degradation,and the irreversible capacity loss of 13.3%is essentially attributed to the unrecoverable interface/structure deterioration of NCM with further hindrance of the aged Li.Moreover,principles of alleviating aging have been proposed.This work bridges academia and industry and enriches the fundamental epistemology of storage aging of LMBs,shedding light on realistic applications of high-energy batteries.