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.

Realizing a“solid to solid”process via in situ cathode electrolyte interface(CEI)by solvent-in-salt electrolyte for Li-S batteries

Lithium-sulfur batteries(LSBs)are regarded as the most promising next-generation energy system due to their high theoretical energy density.However,LSBs suffer the“shuttle effect”if undergoing the solid-liquid-solid sulfur conversion process during cycling.Herein,we design a solvent-in-salt(SIS)electrolyte with co-solvent vinylene carbonate(VC)to synthesize an in situ dense cathode electrolyte interface(CEI)and successfully change sulfur conversion into a solid-solid way to avoid shuttle effect by separating the contact of sulfur and ether solvent.Dense CEI is formed at the beginning of first discharge by the combined action of SIS electrolyte and filmogen VC.Experiments and simulations show that SIS electrolyte controls the initial formed lithium polysulfides(LiPSs)to stay very closely on the cathode surface,and then converts them into a dense CEI film.As a result,Coulombic efficiency(above 99%)and cycling performance of LSBs are improved.Furthermore,the in situ dense CEI can nearly stop the self-discharge of LSBs,and enable the LSBs to work under a pretty lean electrolyte condition.

Charactering and optimizing cathode electrolytes interface for advanced rechargeable batteries:Promises and challenges

With the advancement of secondary batteries,interfacial properties of electrode materials have been recognized as essential factors to their electrochemical performance.However,the majority of investigations are devoted into advanced electrode materials synthesis,while there is insufficient attention paid to regulate their interfaces.In this regard,the solid electrolyte interphase(SEI)at anode part has been studied for 40 years,already achieving remarkable outcomes on improving the stability of anode candidates.Unfortunately,the study on the cathode electrolyte interfaces(CEI)remains in infancy,which constitutes a potential restriction to the capacity contribution,stability and safety of cathodes.In fact,the native CEI generally possesses unfavorable characteristics against structural and compositional stability that requires demanding optimization strategies.Meanwhile,an in-depth understanding of the CEI is of great significance to guide the optimization principles in terms of composition,structure,growth mechanism,and electrochemical properties.In this literature,recent progress and advances of the CEI characterization methods and optimization protocols are summarized,and meanwhile the mutually-reinforced mechanisms between detection and modification are explained.The criteria and the potential development of the CEI characterization are proposed with insights of novel optimization directions.

LiPO_(2)F_(2) electrolyte additive for high-performance Li-rich cathode material

Li-rich layered oxide cathodes have received considerable attention because of the high operating potential and specific capacity. However, the structural instability and parasitic reactions at high potential cause severe degradation of the electrochemical performance. In our studies, the cycling stability of Li_(1.14)Ni_(0.133)Co_(0.133)Mn_(0.544)O_(2) cathode is improved with LiPO_(2)F_(2) electrolyte additive. After 500 cycles, the capacity retention is increased from 53.6% to 85% at 3 C by LiPO_(2)F_(2) modification. This performance is mainly attributed to the enhanced interfacial stability of the Li-rich cathode. Based on systematic characterization, LiPO_(2)F_(2) additive was found to promote a stable interface film on the cathode surface during the cycling and mitigates the interfacial side reactions. This study provides new insights for improving high-potential Li-rich layered oxide batteries.

Review of the electrochemical performance and interfacial issues of high-nickel layered cathodes in inorganic all-solid-state batteries

All-solid-state batteries potentially exhibit high specific energy and high safety,which is one of the development directions for nextgeneration lithium-ion batteries.The compatibility of all-solid composite electrodes with high-nickel layered cathodes and inorganic solid electrolytes is one of the important problems to be solved.In addition,the interface and mechanical problems of high-nickel layered cathodes and inorganic solid electrolyte composite electrodes have not been thoroughly addressed.In this paper,the possible interface and mechanical problems in the preparation of high-nickel layered cathodes and inorganic solid electrolytes and their interface reaction during charge–discharge and cycling are reviewed.The mechanical contact problems from phenomena to internal causes are also analyzed.Uniform contact between the high-nickel cathode and solid electrolyte in space and the ionic conductivity of the solid electrolyte are the prerequisites for the good performance of a high-nickel layered cathode.The interface reaction and contact loss between the high-nickel layered cathode and solid electrolyte in the composite electrode directly affect the passage of ions and electrons into the active material.The buffer layer constructed on the high-nickel cathode surface can prevent direct contact between the active material and electrolyte and slow down their interface reaction.An appropriate protective layer can also slow down the interface contact loss by reducing the volume change of the high-nickel layered cathode during charge and discharge.Finally,the following recommendations are put forward to realize the development vision of high-nickel layered cathodes:(1)develop electrochemical systems for high-nickel layered cathodes and inorganic solid electrolytes;(2)elucidate the basic science of interface and electrode processes between high-nickel layered cathodes and inorganic solid electrolytes,clarify the mechanisms of the interfacial chemical and electrochemical reactions between the two materials,and address the intrinsic safety issues;(3)strengthen the development of research and engineering technologies and their preparation methods for composite electrodes with high-nickel layered cathodes and solid electrolytes and promote the industrialization of all-solid-state batteries.

Ester-based anti-freezing electrolyte achieving ultra-low temperature cycling for sodium-ion batteries

With the continuous advancement of industrialization,sodium-ion batteries(SIBs)need to operate in various challenging circumstances,particularly in extremely cold conditions.However,at ultra-low tem-peratures,the reduced ionic conductivity and sluggish Na+migration of commonly carbonate-based elec-trolytes will inevitably lead to a sharp decrease in the capacity of SIBs.Herein,we design a carboxylate ester-based electrolyte with excellent ultra-low temperature performance by straightforward cosolvent strategy.Due to the low viscosity,melting point,and sufficient ionic conductivity of the designed elec-trolyte,the resulting Na||Na_(3)V_(2)(PO_(4))_(2)O_(2)F can achieve the capacity retention of 96%(100 cycles at 0.1 C)at-40℃ and can also operate stably even at-50℃.Besides,galvanostatic intermittent titration tech-nique(GITT),ex-situ X-ray photoelectron spectroscopy(XPS),and high-resolution transmission electron microscopy(TEM)tests are employed to analyze and confirm that the carboxylate ester-based electrolyte promotes robust and uniform cathode/electrolyte interface layer formation and accelerates ion diffusion kinetics,which collectively facilitates the better low-temperature performance.In addition,the assembled hard carbon||NVPOF full cells further prove the practicability of the carboxylate ester-based electrolyte at low-temperature,which delivers high discharge capacity of 108.4 and 73.0 mAh g^(-1) at-25 and-40℃.This work affords a new avenue for designing advanced low-temperature electrolytes for SIBs.

Surface-targeted functionalization of nickel-rich cathodes through synergistic slurry additive approach with multi-level impact using minimal quantity

LiNi0.8Co0.1Mn0.1O_(2)(NCM811),a Ni-rich layered oxide,is a promising cathode material for high-energy density lithium-ion batteries(LIBs).However,its structural instability,caused by adverse phase transitions and continuous oxygen release,as well as deteriorated interfacial stability due to excessive electrolyte oxidative decomposition,limits its widespread application.To address these issues,a new concept is proposed that surface targeted precise functionalization(STPF)of the NCM811 cathode using a synergistic slurry additive(SSA)approach.This approach involves coating the NCM811 particle surface with 3-aminopropyl dimethoxy methyl silane(3-ADMS),followed by the precise deposition of ascorbic acid via an acid-base interaction.The slurry additives induce the formation of an ultra-thin spinel surface layer and a stable cathode–electrolyte interface(CEI),which enhances the electrochemical kinetics and inhibits crack propagation.The STPF strategy implemented by the SSA approach significantly improves the cyclic stability and rate performance of the NCM811 cathode in both half-cell and full-cell configurations.This work establishes a promising strategy to enhance the structural stability and electrochemical performance of nickel-rich cathodes and provides a feasible route to promote practical applications of high-energy density lithium-ion battery technology.

Adjusting the solvation structure with tris(trimethylsilyl)borate additive to improve the performance of LNCM half cells

Tris(trimethylsilyl)borate(TMSB) has been intensively studied to improve the performances of lithiumion batteries. However, it is still an interesting issue needed to be resolved for the research on the Li^(+) solvation structure affected by TMSB additive. Herein, the electrochemical tests, quantum chemistry calculations, potential-resolved in-situ electrochemical impedance spectroscopy measurements and surface analyses were used to explore the effects of Li^(+) solvation structure with TMSB additive on the formation of the cathode electrolyte interface(CEI) film in LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)/Li half cells. The results reveal that the TMSB additive is easy to complex with Li^(+) ion, thus weaken the intermolecular force between Li^(+) ions and ethylene carbonate solvent, which is benefit for the cycle performance. Besides, the changed Li^(+) solvation structure results in a thin and dense CEI film containing compounds with Si–O and B–O bonds which is favorable to the transfer of Li^(+) ions. As a result, the performances of the LNCM811/Li half cells are effectively improved. This research provides a new idea to construct a high-performance CEI film by adjusting the Li^(+) solvation structures.