| High-capacity NiCoMn ternary cathode materials and silicon-based anode materials have become the preferred cathode and anode materials for high specific energy lithium-ion batteries,however,along with the increase of energy density of high nickel ternary/silicon-based batteries,the battery performance decay accelerates,so it is crucial to explore the performance decay mechanism of high specific energy lithium-ion batteries and establish the accelerated evaluation method of high specific energy battery life to improve the battery life and accelerate the product technology upgrade.In this thesis,3 Ah soft pack laminated lithium-ion batteries are prepared in batch with high nickel 811 ternary material as the cathode material and high capacity silicon-oxygen-carbon composite material as the cathode material,and the influence of charging and discharging multiplier,charging and discharging SOC range and other usage conditions on the decay law of battery cycle performance is investigated,while differential curve,EIS,HPPC and other electrochemical methods and battery disassembly analysis are used to reveal the battery life decay In this paper,we use soft pack lamination process to produce a batch of cells with rich-Ni/SiOx-C cells.115 high specific energy Li-ion batteries with rated capacity of 3 Ah were prepared by soft pack lamination process,and the consistency of battery capacity,voltage and resistance were analyzed by statistical method.50 cells with good consistency were selected as samples for battery electrochemical characterization and cycling characteristics study.The average capacity of the screened battery samples with 0.2C was 3.11 Ah,the average internal resistance was 5.76mΩ,and the 2C capacity retention rate was 94.5%.The quasi-equilibrium state method was used to determine the battery capacity differential curve and voltage differential curve characteristics,in which the charging dQ/dV curve characteristic peak potentials were 3.54 V,3.87 V and 4.09 V,and the positions of the discharge characteristic peaks were 3.26 V,3.73 V and 4.03 V.The area decay of the two characteristic peaks at low potentials during the charging process and the negative electrode activity The decay of the area of the two characteristic peaks of the low potential during the charging process and the loss of active material in the negative electrode are correlated,and the change of height of the characteristic peak of the high potential and the potential shift of the characteristic peak of the low potential during the discharge process both reflect the loss of active lithium ions.The charging dV/dQ curves show two peaks around 50%SOC and 80%SOC,where the peak around 50%SOC is related to the negative electrode and the peak around 80%SOC is related to the positive electrode.The effects of cycling multipliers（0.2C,1.0C,1.5C and 2.0C）on the 100%DOD cycling performance of the battery at room temperature and the intrinsic mechanism of battery life decay at different cycling multipliers were investigated.It is shown that the capacity decay of the battery shows two decay modes at all four multipliers,namely the early stage of smooth decay and the middle and late stage of accelerated decay,and the battery capacity,internal resistance and median voltage follow the same change pattern with cycling in the measured multiplier range.The results of dQ/dV,dV/dQ curves and battery disassembly analysis show that the performance and electrode structure of the high nickel 811 cathode material do not decay and age significantly during different cycles..Meanwhile,cycling at 0.2C-2C magnification range,the battery decay mechanism does not change,so 2C magnification cycling can be used for accelerated life evaluation of rich-Ni/SiOx-C battery,cycling at 2C magnification,the time required for battery decay to life termination（80%capacity retention）is about 27 days,compared with 0.2C cycling,the test time is shortened by 191 days,which has a significant accelerating effect on the battery life The evaluation had a significant accelerating effect on the battery life.The effects of two categories with a total of six SOC ranges on the battery cycling performance were investigated.The first category was 50%DOD cycling,with three different SOC ranges of 0-50%,30-80%and 50-100%selected,and the second category was 80%DOD cycling,with three different SOC ranges of 0-80%,10-90%and 20-100%selected.The results show that the performance of 30-80%SOC and 50-100%SOC cycles is similar when cycling in the 50%DOD range,and the equivalent cycling 400-week capacity retention rate is 93.63%and 92.19%,respectively,while the capacity decay of 0-50%SOC cycles intensifies,and the equivalent cycling 400-week capacity retention rate is only 75.42%;when cycling in the 80%DOD range The battery cycling performance improved sequentially with the increase of the lower SOC limit,and the equivalent cycling 400-week capacity retention rates were 85.15%,89.00%and 91.75%for 0-80%,10-90%and 20-100%,respectively,and the lower SOC limit had a more significant negative impact on the battery cycling performance compared with the upper SOC limit.The results of dQ/dV,dV/dQ curves and electrochemical and XRD/SEM/XPS characterization after battery disassembly showed that the loss of anode active material and active lithium ion were the main causes of battery performance degradation when cycled in the range of 0-50%,0-80%and 0-100%SOC,and with the increase of the lower SOC limit,the loss of anode active material and active lithium ion The 0-50%SOC cycling pattern and decay mechanism are similar to 100%DOD cycling,which can be used for accelerated life test of rich-Ni/SiOx-C battery.59 days,and the accelerating effect of the SOC range on life is not significant compared to the charge/discharge multiplier. |
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