In order to solve the problems of insufficient adsorption electrolyte capacity and small specific surface area caused by the smooth surface and few pores of Super P spherical conductive particles, this work uses concentrated sulfuric acid (H 2 SO 4 ) for surface etching of Super P conductive particles to explore the influence of different etching time on the micromorphology of SP conductive agent and the behaviors of LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM-523) batteries. After etched by concentrated H 2 SO 4 , the surface of SP conductive agent changes from “capillary” structure to fluffy “plush” structure, effectively improving the conductivity specific surface area of the conductive agent particles. Compared with the pristne SP-0H conductive agent, the batteries using 1.5% of concentrated H 2 SO 4 etched SP-1H, SP-2H and SP-20H conductive agent have smaller EIS impedance value, larger area of CV curves, and smaller potential difference of the redox peaks. As a result, the initial charging/discharging capacities of SP-1H, SP-2H and SP-20H conductive batteries were 178.7/183.0, 187.6/183.9, 178.9/180.8 mAh/g with corresponding ICE of 102.4%, 98.0% and 101.1% respectively, which were much higher than the pristine SP-0H conductive battery (182.0/173.7 mAh/g with ICE of 95.4%). In addition, the SP-1H, SP-2H and SP-20H batteries also show significantly improved cycle performance and rate cycle capabilities, showing more superior comprehensive behaviors, which can provide a new modification insights for the exploration of new conductive agent in NCM-523 of high-performance lithium ion batteries.
Increasing the working voltage of lithium-ion batteries (LIBs) is an efficient way to increase energy density. However, high voltage triggers excessive electrolyte decomposition at the electrode–electrolyte interfaces, where the electrochemical performance such as cyclic stability and rate capability is seriously deteriorated. A new synergistic positive and passive approach is proposed in this work to construct a stable electrode–electrolyte interface at high voltage. As a positive approach, inorganic lithium sulfide salt (Li2S) is used as an electrolyte additive to build a stable cathode electrolyte interface (CEI) at the LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode surface. In a passive way, acetonitrile (AN) is applied as a solvent additive to suppress oxidative decomposition of a carbonate electrolyte via preferential solvation with a lithium ion. Because of the synergistic interaction between the positive and passive approaches, the cyclic stabilities of NCM523/Li cells improved with a tiny amount of Li2S (0.01 mg mL–1) and AN (0.5 vol %). The capacity retention increased to 80.74% after 200 cycles compared to the cells with the blank electrolyte (67.98%) and AN-containing electrolyte (75.8%). What is more, the capacity retention of the NCM523/graphite full cell is increased from 65 to 81% with the addition of the same amount of Li2S and AN after 180 cycles. The mechanism is revealed on the basis of the theoretical calculations and various characterizations. The products derived from the preferential adsorption and oxidation of Li2S on the surface of NCM523 effectively increase the content of inorganic ingredients. However, the presence of AN prevents oxidation of the solvent. This study provides new principle guiding studies on a high-voltage lithium-ion battery with excellent electrochemical performance.
Increasing working voltage is a promising way to increase the energy density of lithium-ion batteries. Cycling and rate performance deteriorated due to excessive electrolyte decomposition and uncontrolled formation of a cathode–electrolyte interface (CEI) layer at a high voltage. A new concept is proposed to construct a high-voltage-stable electrode–electrolyte interface. An elastomeric poly(dimethyl siloxane) (PDMS) binder is incorporated into the electrode to modify the LiNi0.5Co0.2Mn0.3O2 (NCM 523) particle surface via an in situ cross-linking reaction between hydroxy-terminated PDMS and methyl trimethoxy silane promoted by moisture at ambient conditions (MPDMS). Improved electrochemical performance is achieved with the MPDMS binder in terms of reversible capacity (201 vs 185 mAh·g–1 at 0.2C), capacity retention (80 vs 68%, after 300 cycles at 1C), and rate performance (55.6% increase at 5C), as demonstrated by the NCM 523||Li half-cell. The NCM 523||graphite full-cell also shows improved performance at 4.6 V (147 vs 128 mAh·g–1, 82 vs 76%, after 200 cycles at 1C). The mechanism studies indicate that MPDMS exerts multiple effects, including cathode surface passivation, solvation structure tuning, electrolyte uptake enhancement, and mechanical stress relief. This work provides an inspiring route to realize high-voltage application of lithium-ion battery technology.
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