Regulating Tin-based Lithium Storage Anode Materials And Electrolytes For The Low Temperature Applications

Li-ion batteries(LIBs)with graphite anode is suffering from capacity decline,non-chargeability and poor safety at low temperatures,which seriously restricts the sustainable development of new energy vehicles with LIBs systems.To improve the lithium storage capacity of LIBs at low temperatures,it is important to develop new anode materials and construct a stable interface structure between anode and electrolyte.In this work,to overcome the low-temperature capacity decrease of the anode electrode in LIBs,the influence of the electrode reaction potential and microstructure tuning on the lithium storage capacity were carefully analyzed for the anode materials.Characterization techniques such as SEM,TEM FTIR and XPS,and electrochemical methods such as CV,AC impedance and constant current CD were applied to carefully investigate the mechanism of temperature on the reversibility and stability of lithium storage in Co₃O₄and SnO₂anode.The lithium storage stability and reversible capacity of the SnO₂-based composites under wide temperatures were effectively improved through reasonable surface/interface modification.Furthermore,in order to realize the fast charging capability of the Sn-based cathode under a lower temperature,regulation and optimization were done for the electrolyte.The main results are as follows:First,for the capacity drop and poor stability of the anode at low temperatures,in this work,the effects of reaction potential and theoretical specific capacity of anode on lithium storage capability under low-temperature are discussed in detail by systematically comparing the electrochemical performance of anode materials with different reaction potentials at different temperatures.It is revealed that high lithium storage potential and high theoretical specific capacity of 890 mAhg^-1in Co₃O₄anode ensure its good capacity retention at temperatures as low as-30°C.The layer-like structure was successfully prepared for Co₃O₄@G composite by a one-step hydrothermal method,and it is demonstrated that nano-sized Co₃O₄particles and sheet-like graphene layer can effectively shorten the diffusion path of lithium ions,reduce the internal resistance under low-temperature and protect the structural integrity of the electrode.The Co₃O₄@G electrode can maintain a reversible specific capacity of 605.0 mAhg^-1after 600 cycles with a high current density of 1Ag^-1under-10°C.Furthermore,a Co₃O₄@G||Li Co O₂full cell was assembled,which demonstrates the excellent lithium storage capacity and stability of Co₃O₄@G anode at low temperature.Then,based on the thermal-sensitive characteristics of Sn-based anode materials,the SnO₂thin film anode was prepared by vapor deposition method.The influence of temperature on the reversibility and stability of lithium storage was investigated in depth for SnO₂anode.It is revealed that low temperature can effectively inhibit the coarsening of Sn particles during lithium storage,stabilize the Sn/Li₂O phase interface ratio and the liquid-solid interface film on the electrode surface,and improve the cycling stability of SnO₂electrodes.In addition,the transition from?-Sn to?-Sn phase under low-temperature was confirmed by the self-developed low-temperature in-situ XRD technique.Theoretical calculation show that?-Sn possesses a lower Li⁺embedding energy barrier than that of?-Sn.As a result,the SnO₂electrode can deliver a reversible specific capacity of 603.1 mAhg^-1at-20°C,which is 71%of its capacity at 30°C.After 100 cycles,it still maintains a specific capacity of 423.8 mAhg^-1at-30°C.Compared with other material systems in the same electrolyte,the SnO₂anode has the highest capacity retention rate at low temperature.Afterward,thermally induced Sn particles coarsening and poor Li⁺diffusion kinetics under low temperatures are the main contradictory issues forward the lithium storage requirement of Sn-based anode materials at wide temperatures.In this work,LiF and graphite components were introduced in the SnO₂system by mechanical milling,and their effecting mechanisms on the lithium storage performance of SnO₂anode were thoroughly explored under wide temperature.The electrochemical properties at different temperatures were tested to demonstrate that the synergistic effect of LiF and graphite effectively suppress the coarsening of Sn particles during the cycling,enhances the cycling stability and low-temperature lithium storage performance of the SnO₂-LiF-G electrode.Thus,SnO₂-LiF-G electrode with a current density of 2Ag^-1can still maintain a high specific capacity of 752mAhg^-1in 30°C even after 600 cycles;And a high specific capacity of 393.9 mAhg^-1was obtained in-30°C as well.it is confirmed that LiF can effectively improve the reversibility of the conversion reaction in the SnO₂active phase,and induce the generation of lithium-rich inorganic substances on the electrode surface,which effectively mitigate the catalytic decomposition of the electrolyte under the high-potential region and restrain the abnormal growth of the irreversible capacity.SnO₂-LiF-G||LiFe PO₄full cell was also assembled to demonstrate the charging and fast charging capabilities of SnO₂-LiF-G anode under low-temperature.Finally,to further improve the reversible lithium storage capacity of Sn-based anode under lower temperatures,in this work,the lithium storage performance of SnO₂-LiF-G anode in lower temperature environment was investigated carefully with low-polarity solvent THF and 2Me-THF-based low-temperature electrolyte.Compared with conventional electrolytes,Li PF₆-(THF/2Me-THF)electrolyte exhibits low polarity,low melting point and low de-solvation energy due to its low dielectric constant solvent composition.The SnO₂-LiF-G electrode with Li PF₆-(THF/2Me-THF)electrolyte can provide a high reversible specific capacity of 731 mAhg^-1at-50°C.Besides,it is revealed that the SnO₂-LiF-G electrode exhibits a stable cycling capacity with Li PF₆-(THF/2Me-THF)electrolyte under low temperature or exhibited a stable cycling capacity with Li PF₆-(THF/2Me-THF)-FEC electrolyte under room temperatures,which was positively related to the larger proportion of lithium-rich inorganic components on the electrode surface.The present results provide a basis for further development of low-temperature electrolytes of Li-ion batteries.