An argyrodite-type sulfide solid electrolyte Li₆PS₅Cl (LPSC) was solid-phase synthesized by adopting high energy ball milling in combination with heat treatment. It is found that prolonging ball milling time is conducive to crushing, mixing, grain refinement and amorphization reaction process of raw material powder; increasing sintering temperature is beneficial to the formation of a single pure phase, but too high temperature for sintering can make electrolyte melted and decomposed, leading to destroyed crystal structure. It is found that after 10 hours of ball milling and 8 hours of sintering at 550 ℃, the synthesized sulfide solid electrolyte exhibits higher ionic conductivity, reaching 3.57×10^-3S/cm.

Lithium sulfide was prepared by solid phase syntheses, with lithium metal as the lithium source, sulfur powder as the sulfur source, and lithium nitride as the additive. Thermodynamic analysis results show that lithium nitride can promote the reaction of lithium metal with sulfur powder to synthesize lithium sulfide; Li₃N firstly reacts with sulfur powder to release N₂, leading to holes formed on the molten lithium metal sheet and the contact area between lithium metal and sulfur powder further expanded. Thus a loose and porous skeleton structure is formed, which is conducive to subsequent crushing and can reduce the risk of secondary reactions in the following ball milling process. With Li∶S∶Li₃N=2∶2∶0.4 (molar ratio), crude lithium sulfide can be obtained after 8 hours reaction at 100 ℃. It is then subjected to calcination, impurity removal and ball milling processes, and a kind of lithium sulfide products with purity greater than 99.95% and particle size less than 15 μm can be obtained, which can be used in EV. This method provides a new idea for industrial production of lithium sulfide products.

A single-factor experiment was conducted to explore the influence of rotation speed and lateral swing speed of polishing brush, and polishing current on the performance of copper foil and pinholes. Based on that, the polishing process was also optimized by applying response surface methodology, and thus the performance and apparent quality of copper foil was also improved. The results show that by using on-line polishing, with the rotation speed of the polishing brush at 450 r/min, the lateral swing speed of 350 r/min, and the polishing current of 0.50 A, the smooth surface (S surface) of the generated copper foil is uniform, and the pinhole defects are significantly reduced.

A kind of hydrogen storage alloy of La_0.7R_0.1Mg_0.2Ni_3.35Al_0.15 (R=La/Nd/Sm) was synthesized with induction melting method, and the effect of La substituted with rare earth element Nd/Sm on the phase structure, microstructure, and electrochemical performance of the hydrogen storage alloy was explored. The results show that the substitution of Nd or Sm for La doesn't change the phase composition of the hydrogen storage alloy, which is still composed of LaNi₅, (LaMg)₂Ni₇, and (LaMg)₅Ni₁₉ phases, but leads to higher abundance of LaNi₅ and (LaMg)₅Ni₁₉ phases, and lower abundance of (LaMg)₂Ni₇ phase in the hydrogen storage alloy. The hydrogen storage alloy, with La, Nd and Sm as R, deliver the maximum discharge capacities of 377 mAh/g, 382 mAh/g and 376 mAh/g, respectively, after the second charge-discharge cycle. With La substituted with Nd or Sm, the hydrogen storage alloy has its high-rate discharge capacity, the charge retention rate after 24 hours, and capacity retention rate after 100 cycles all improved to some extent, among which the hydrogen storage alloy with Nd as R is the best in all corresponding performance. Moreover, the substitution of La with Nd or Sm can make the hydrogen storage alloy with higher exchange current density and higher coefficient of hydrogen diffusion. Its high-rate discharge performance, exchange current density and hydrogen diffusion coefficient are all in in the same trend, indicating that high-rate discharge performance of the hydrogen storage depends on both exchange current density and hydrogen diffusion coefficient.

In order to improve the accuracy of the GRU neural network model in predicting the remaining useful life (RUL) of lithium-ion batteries, the GRU model was optimized based on PCA-GWO and then applied in the prediction. The results show that compared with the traditional GRU model, the PCA-GWO-GRU model presents higher prediction accuracy. When the starting point of the prediction is 90% of the original data, the prediction accuracy can reach the highest, with the corresponding RMSE of 0.004 9, MAE of 0.003 6, and R² of 0.986 3.

An experiment was conducted on selective extraction of lithium by co-pyrolysis of spent NCM cathode powder and polypropylene followed by water leaching, and the obtained pyrolysis products were characterized. In the experiment, co-pyrolysis of NCM cathode powder with 40% polypropylene ran at 550 ℃ for 2 h, with argon flow rate at 200 mL/min, and then the obtained pyrolysis product was subjected to water leaching, resulting in the lithium leaching rate of 87.92%. It is found that lithium loss is mainly attributed to the formation of water-insoluble lithium cobalt oxide during co-pyrolysis.

Cathode and anode materials in spent lithium iron phosphate battery powder are difficult to be separated by flotation. In order to solve this problem, it was proposed that lithium iron phosphate battery powder was pretreated by oxidative roasting, and then subjected to a flotation process for seperation between the cathode and anode materials of lithium iron phosphate. The results show that after lithium iron phosphate battery powder is pretreated by oxidative roasting at 500 ℃ for 30 minutes, the subsequent flotation process can lead to the graphite-based anode material with carbon grade up from 47.63% to 97.70%, and the cathode material with carbon grade down from 24.00% to 1.01%, presenting a significant separation effect. In comparison, the battery powder without pretreatment has cobweb-like long carbon-chain organic matter on its surface, which causes adhesion between cathode and anode materials of batteries, resulting in poor separation effect by flotation. The pretreatment of oxidative roasting can effectively eliminate the long carbon-chain organic matter on those cathode and anode materials, thus enhancing the difference in surface properties between cathode and anode materials. As a result, the enhanced flotation separation effect makes graphite-based anode material recycled from spent lithium iron phosphate batteries.

In order to recover metal elements from the cathode materials of spent Li-ion batteries in an environmentally friendly and efficient way, three deep eutectic solvents (DES) were synthesized with choline chloride as hydrogen bond acceptor, malonic acid, succinic acid and adipate respectively as hydrogen bond donors. Then, Co and Li in the cathode materials of spent Li-ion batteries were leached by adopting these three DESs respectively. The effects of leaching time, liquid-solid ratio and reaction temperature on the leaching rates of Co and Li were explored, and the leaching residues were also characterized in terms of morphology and phase. The leaching mechanism was analyzed by FT-IR spectrum and UV-Vis absorption spectrum. It is shown that the leaching efficiency of metal elements can be enhanced by prolonging leaching time, increasing liquid-solid ratio and temperature. It is found that under the optimal conditions, including leaching time of 300 minutes, liquid-solid ratio of 100 mL/g, and temperature of 110 ℃, malonic acid-based DES, among those three kinds of DESs, can bring better leaching effect, with leaching rates of Co and Li all exceeding 99%. During the leaching of lithium cobalt oxide with those three DESs, Co exists in the form of bivalent in the leaching solution, and the coordination compound is in a tetrahedral structure.

With the calcium-magnesium slag generated in recycling process of spent Li-ion batteries as raw material, battery-grade lithium carbonate was prepared by adopting a process consisting of leaching for decomposition, purification, lithium precipitation and carbonization for decomposition. The results show that with the addition of MgSO₄·7H₂O at 1.1 times of the theory amount, initial pH of 1.5, reaction time of 2.0 h, solid-liquid ratio of 1∶6, reaction temperature of 90 ℃, and final pH of 3.5, the leaching rate of Li can reach 98.39% and the mass concentration of Li in the lixivium is 18.03 g/L. Then, the obtained lixivium is subjected to processes of defluorination with resin, impurity removal with NaOH, and Na₂CO₃ precipitation, and crude lithium carbonate can be obtained with purity of 95.11%. By adopting a process consisting of carbonization, removal of calcium and magnesium with resin, and pyrolysis, a battery-grade lithium carbonate with purity of 99.64% can be prepared. It is shown that by using this processing technique, the lithium recovery rate can reach 95.08%, presenting good prospect in industrial application.

A review of comprehensive recycling technologies for graphite anodes in spent lithium-ion batteries is presented, including hydrometallurgical process, a combination of pyrometallurgical and hydrometallurgical process, as well as mechanical recycling. And then, an in-depth analysis of advantages and disadvantages of each technology is also presented. It is particularly pointed out that there are various recycling technologies, but the development of an efficient and environmentally-friendly closed-circuit recycling process still faces challenges. The recycling approaches of graphite anodes in spent lithium-ion batteries are discussed in details, such as usage as anodes of rechargeable batteries, or for preparation of graphene. The research direction in the future is also forecasted aiming to provide theoretical and technical support for reutilization of graphite anodes in spent lithium-ion batteries with high-value added. It is suggested that research should focus on developing a simple, efficient and clean closed-circuit recycling processes to improve the recovery rate and purity of graphite anode materials while reducing environmental pollution. The research hotspots in the future should include lattice reconstruction and repairing technologies for graphite anode materials, as well as exploration of new applications of graphite anode materials in the fields of energy storage materials, catalysts, adsorbents among others.