| Lithium/sodium-ion batteries（LIBs/SIBs）as the most popular energy storage devices are attracting the extensive research interests in the field of electrochemical energy storage.As the key part of the battery,the anode materials have a crucial influence on the electrochemical performance of the battery.At present,the commercial anode material of lithium-ion batteries is the graphite material,but graphite material has a low theoretical specific cap acity and a small layer spacing,which limit the improvement of energy density in lithium-ion batteries.It is urgent to develop a type of high-capacity anode material for lithium/sodium-ion batteries.In view of the unique two-dimensional layered structure and high electronic conductivity,the metal chloride intercalated graphite intercalation compounds（GICs）have been extensively studied as the potential anode materials.However,due to its easy dissolution of metal chloride in the electrolyte during cha rge and discharge processes,the cycle performance of the GIC is usually poor caused by the loss of active materials and structural collapse.In this thesis,the research purpose will strive to explore an effective strategy that can significantly improve t he cycle life of metal chloride intercalated GICs.The research works focus on the structural design and composition optimizing of the GIC anodes,further tailor the state of charge between the adjacent graphite layers,and study the mechanism of lithium/sodium-ion storage.The three parts of research works are summarized as follows:1.To solve the problem of poor cycling stability of FeCl 3-GICs caused by the dissolution of chloride,the components of GICs was purposely designed based on the principle of"polar–polar interaction".Herein,a part of FeCl3 on the edge of the GICs was transformed into flake Fe2O3 by the microwave-assisted oxidation method.The introduced Fe2O3 component can provide enough polar active sites to combine soluble FeCl3 and LiCl species,further inhibiting the outward diffusion of metal chloride and fixing it in the GICs.Moreover,the discharge product in the GIC anode was prove to be the stable CLi compound,rather than traditional C6Li product.In a lithium-ion cell,the FeCl3-intercalated GIC with a suitable Fe 2O3 content shows remarkably improved cycling stability with a high reversible capacity of 1,041 m Ah?g-1 at a current density of 200 m A?g-1.Capacity retention of 91%is achieved at a high current density of1,000 m A?g-1 over 300 cycles.2.To avoid the dissolution and escape of metal chlorides from GICs,the AlCl3-intercalated GICs were employed as the research object to investigate the effect of the electrolyte composition on the sodium-ion storage performance.Herein,the electrochemical properties of the AlCl3-GICs as anode materials of SIBs were systematically studied in the ether-based electrolytes,compared with those in the ester-based electrolytes.The results show that the GIC anodes possess the best structural integrity in the diethylene glycol dimethyl ether（DEGDME）-based electrolyte.Such AlCl3-GIC anode could provide a reversible capacity of 198 m Ah g-1after 900 cycles at a current density of 0.5 A g-1.3.The theoretical calculation found that MoCl5 has higher binding energy with graphite layer compared with the conventional FeCl 3 guest.Thus,the MoCl5-intercalated GICs with adjustable stage 1 and stage 2 structures were elaborately prepared through the modified molten salt method.The inserted MoCl5monolayer could induce a strong charge transfer chemical doping effect between the graphite layers,thus endowing the GICs with a high electronic conductivity of 2.8×105 S cm-1.The MoCl5-GIC anode delivered high gravimetric and volumetric capacities of 275 m Ah g-1 and 426 m Ah cm-3 for sodium-ion storage,respectively.For the LIBs,a reversible storage capacity of 1099 m Ah g-1(1703 m Ah cm-3)is stably maintained during 100 cycles.The strong interaction force between MoCl 5 and graphite layers helps to firmly immobilize soluble chlorides during repeated charge/discharge processes,leading to excellent sodium storage cyclability with nearly no capacity loss during 1000 cycles. |
