As a promising anode material, silicon has attracted extensive attention. The instability of the electrode/electrolyte interphase due to the inherent volume variation upon (de)lithiation is one of the major factors limiting the commercialization of silicon anode materials. Here, we report a concentrated electrolyte with lithium bis(fluorosulfonyl)imide (LiFSI) and lithium difluoro (oxalate) borate (LiDFOB) dual salt to enhance the control of the species constituting the solid electrolyte interphase (SEI) on the surface of the silicon material. The silicon nanoparticle (SiNP) electrode with the dual‐salt LiFSI0.7LiDFOB0.3‐(PC)4 concentrated electrolyte delivers a relatively high average coulombic efficiency of 97.68 % and a remarkably improved cycling performance with an initial capacity of approximately 3300 mAh g−1 and a capacity retention around 2000 mAh g−1 after 100 cycles. It is found that the polarity of the B−F bond of LiDFOB decreases when the molar ratio of LiDFOB to LiFSI is greater than 0.3 : 0.7. Therefore, the reduction of LiDFOB through a ring‐opening reaction coupled with a ring‐opening reaction of PC becomes dominant. The SEI layer rich in the corresponding products Li(BF2O)n polymer could suppress the rupture of the Si particles and excessive growth of the SEI layer, thus could further mitigate the decrease of coulombic efficiency.

The entropic heat coefficient (i.e., dU/dT) of Li[Ni x Co y Mn z ]O 2 /graphite before and after cycle was determined using the electrochemical thermodynamics measurements (ETMs) tool. DU/dT could be attributed to the individual electrodes for this notable battery and associates with the Li-intercalated state. Lithium intercalation number in negative and positive electrode was calculated and compared for the battery before and after cycle, respectively. Results show that the trend of dU/dT with Li-intercalated state before and after cycle is basically consistent except for the initial and maximum state. DU/dT has the typical characteristics of stage structures of graphite. In particular, these changes is independent of the battery aging. Negative electrode has greater Li-intercalated depth loss than that of positive electrode after cycle, thus negative electrode is the dominant degradation factor of the battery.

The present work focuses on the state-of-charge (SOC) estimation of a lithium-ion battery in terms of a second-order extended Kalman filter (EKF). First, an equivalent circuit model is introduced to describe the performance of lithium-ion batteries. The model parameters are then identified through hybrid pulse power characterization experiments conducted over a wide range of temperatures (−10 to 55 • C). A two-dimensional mathematical relationship is established with respect to the SOC and temperature based on a dual-fifth polynomial expression. The main effects and sensitivities of the SOC and temperature on the parameters are analysed according to the principle of variance analysis and partial derivatives. An estimation algorithm is developed, which combines the two-dimensional parameter model and second-order EKF. Finally, the proposed approach is validated compared to other estimation schemes through discharge experiments under extreme temperatures and dynamic loading profiles, which yields experimental results that estimate the SOC with an absolute error of less than 4.5% under harsh conditions. This not only demonstrates that it can characterize dependency of the model parameters on the operating conditions and address the uncertainty of model parameters, but also verifies the advantage of present method at low temperatures especially at sub-zero temperatures.

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