Doping Modification Of Lithium Titanate And Their Electrochemical Performance In A Low Temperature

Rechargeable lithium batteries（RLBs）have received considerable attention in electrochemical energy storage（EES）devices due to their sustainability,environmental friendliness,time and space transferability.However,most RLBs are only used in conventional environments,and commercial graphite lithium-ion batteries will not function when exposed to low temperatures（below 0℃）for a long time.Therefore,exploring high safety anode materials that can replace graphite has become crucial.Lithium titanate（LTO）is a high potential anode material that can avoid battery short circuits caused by the deposition of lithium metal on the electrode surface,thereby enhancing the safety of the battery.However,its low ionic and electronic conductivity have long been considered key factors in reducing its performance.Moreover,there is limited research on the electrochemical performance of lithium titanate anode materials at low temperatures,and further development is needed.Based on this,this paper aims to improve the electrochemical performance of lithium titanate based materials at room and low temperatures.By preparing micro and nano scale heteroatom doped lithium titanate based materials,the effects of different optimization methods on the wide temperature lithium storage performance of lithium titanate were systematically studied.It mainly includes the following content:1)The precursor of lithium titanate nanosheets prepared by hydrothermal method was mixed with copper acetate,evaporated in a water bath,and finally calcined to prepare copper doped lithium titanate（Cu-LTO）nanosheets.Explored the electrochemical performance of different Cu doping contents from 1 to 3 wt.%,and found that 2 wt.%Cu doped lithium titanate has higher rate performance and stable long cycle at room temperature,with a discharge capacity of approximately 187 mAh/g at 0.1 A/g and 152 mAh/g at 5 A/g.And the capacity retention rate after more than 1000 cycles is higher than 92%.Electrochemical testing was conducted at low temperatures.At temperatures of-10℃,-20℃,and-30℃,Cu-LTO can provide discharge specific capacities of approximately 187 mAh/g,179 mAh/g,and 178 mAh/g at a current density of 0.1A/g,respectively.2)This article prepared a W doped lithium titanate/brookite layered porous nanocomposite material through composition design.Its microstructure is a graded micrometer level spherical structure formed by the aggregation of ultra-thin nanosheets,in which more space can be seen.The appearance of these vacancies improves the wettability of the sample to the electrolyte.In addition to doping with heteroatoms,this material achieves the composite of brookite and lithium titanate by controlling the lithium titanium ratio,and at the same time controls the temperature of heat treatment to obtain a suitable crystal form-perovskite.Compared to lithium titanate,brookite has a higher specific capacity,which is beneficial for improving the specific capacity of composite materials.Moreover,the phase boundary also provides additional capacity,making it also have excellent electrochemical performance at low temperatures.The W doped LTO/brookite can provide a discharge specific capacity of approximately 205 mAh/g at a current density of0.1 A/g at-20℃,achieving a reversible specific capacity of～195 mAh/g for the first discharge,which is much greater than the theoretical capacity of commercial LTO.3)Lithium titanate/MXene nanosheets with large specific surface area were prepared by hydrothermal method using ammonium molybdate as the Mo source and sulfur powder as the S source.The specific surface area（SSA）of Mo,S-LTO/Mx can reach 145 m²/g.Electrochemical testing was carried out by combining it with lithium flakes to form a half cell and Li Fe PO₄ to form a full cell.Experiments have shown that Mo,S co-doped lithium titanate/MXene nanosheets can provide a discharge specific capacity of 153 mAh/g at a current density of 2 A/g at a temperature of-20℃.For the cycling performance at-20℃,the reversible capacity of Mo,S-LTO/Mx remains at 164 mAh/g（with a capacity retention rate of 92%）.Density functional theory（DFT）calculations indicate that co doping of Mo and S can introduce impurity levels,improve the electronic conductivity of LTO,and improve its electrochemical performance.4)We have explored the application of Cu-LTO in dual ion batteries.In order to further improve the energy density of lithium titanate full batteries,N,P doped graphite was designed and combined with Li Mn₂O₄ to utilize anionic and cationic storage,achieving greater capacity and higher operating voltage through deep cycling.The entire battery was assembled using activated Graphite-Li Mn₂O₄ and Cu-LTO as electrodes and Li PF₆ as electrolyte,and electrochemical performance tests were conducted.Electrochemical measurements have shown that compared to traditional LIBs,the assembled full battery can operate at a voltage of over 3.5V,compensating for the energy loss caused by the high voltage of the lithium titanate platform and improving the energy density of the lithium titanate full battery.And the full battery fully utilizing the movable ions in the electrolyte and electrode for energy storage,shows higher capacity and stable cycling performance（with a capacity retention rate of 76%after 600 cycles at 100 m A/g）in the temperature range of-20 to 25℃.