The electrochemical performance of hard carbon(HC)materials is closely related to the electrolyte used in the sodium ion batteries(SIBs).Conventional electrolytes carbonate(EC)demonstrates low initial Columbic efficie...The electrochemical performance of hard carbon(HC)materials is closely related to the electrolyte used in the sodium ion batteries(SIBs).Conventional electrolytes carbonate(EC)demonstrates low initial Columbic efficiency(ICE)and poor rate performance,which is one of the main bottlenecks that limits the practical application of HCs.Ether electrolyte(diglyme)was reported to improve the rate performance of HCs.Nevertheless,the underlying mechanism for the excellent rate capability is still lack of in-depth study.In this work,the differences of sodium-ion diffusion between ether and carbonate-base electrolytes in HCs are analyzed layer by layer.Firstly,when sodium-ions are diffused in electrolyte,the diffusion coefficient of sodium-ion in ether electrolyte is about 2.5 times higher than that in ester electrolytes by molecular dynamics(MD)simulation and experimental characterization.Furthermore,when the solvated sodium-ions are diffused into the solid electrolyte interphase(SEI)interface and the HCs material,the enhanced charge transfer kinetics(thin SEI layer(4.6 vs.12 nm)and low RSEI(1.5 vs.24Ω))at the SEI combined with low desolvation energy(0.248 eV)are responsible for high-rate performance and good cycling stability of HC in ether electrolyte.Therefore,high diffusion coefficient,low desolvation energy,and good interface are the intrinsic reasons for enhanced rate performance in ether electrolyte,which also has guiding significance for the design of other high-rate electrolytes.展开更多
Due to its high operational voltage and energy density,P2-type Na_(0.67)Ni_(0.3)Mn_(0.7)O_(2) has become a leading cathode material for sodium-ion batteries(SIBs),which is an ideal option for large-scale energy storag...Due to its high operational voltage and energy density,P2-type Na_(0.67)Ni_(0.3)Mn_(0.7)O_(2) has become a leading cathode material for sodium-ion batteries(SIBs),which is an ideal option for large-scale energy storage.However,the practical application of P2-type Na_(0.67)Ni_(0.3)Mn_(0.7)O_(2) is limited by the capacity constraints and unwanted phase transitions,presenting significant challenges to the widespread application of SIBs.To address these challenges and optimize the electrochemical properties of the P2 phase cathode material,this study proposes a Cu and Zn co-doped strategy to improve the electrochemical performance.The incorporation of Cu/Zn can stabilize the P2-phase structure against P2-O2 phase transitions,thus enhancing its electrochemical properties.The as-obtained P2-type Na0.67[Ni_(0.3)Mn_(0.58)Cu_(0.09)Zn_(0.03)]O_(2) cathode material shows an impressive cycling stability,maintaining 80%capacity retention after 1000 cycles at 2 C.The cyclic voltammetry(CV)tests show that the Cu^(2+)/Cu^(3+)redox reaction is also involved in charge compensation during the charge/discharge process.展开更多
基金supported by the National Natural Science Foundation of China(Nos.22179077,51774251,and 21908142)Shanghai Science and Technology Commission’s“2020 Science and Technology In-novation Action Plan”(No.20511104003)Natural Science Foundation in Shanghai(No.21ZR1424200).
文摘The electrochemical performance of hard carbon(HC)materials is closely related to the electrolyte used in the sodium ion batteries(SIBs).Conventional electrolytes carbonate(EC)demonstrates low initial Columbic efficiency(ICE)and poor rate performance,which is one of the main bottlenecks that limits the practical application of HCs.Ether electrolyte(diglyme)was reported to improve the rate performance of HCs.Nevertheless,the underlying mechanism for the excellent rate capability is still lack of in-depth study.In this work,the differences of sodium-ion diffusion between ether and carbonate-base electrolytes in HCs are analyzed layer by layer.Firstly,when sodium-ions are diffused in electrolyte,the diffusion coefficient of sodium-ion in ether electrolyte is about 2.5 times higher than that in ester electrolytes by molecular dynamics(MD)simulation and experimental characterization.Furthermore,when the solvated sodium-ions are diffused into the solid electrolyte interphase(SEI)interface and the HCs material,the enhanced charge transfer kinetics(thin SEI layer(4.6 vs.12 nm)and low RSEI(1.5 vs.24Ω))at the SEI combined with low desolvation energy(0.248 eV)are responsible for high-rate performance and good cycling stability of HC in ether electrolyte.Therefore,high diffusion coefficient,low desolvation energy,and good interface are the intrinsic reasons for enhanced rate performance in ether electrolyte,which also has guiding significance for the design of other high-rate electrolytes.
基金supported by the National Natural Science Foundation of China(Nos.22179077,51774251,21908142)Shanghai Science and Technology Commission’s“2020 Science and Technology In-novation Action Plan”(No.20511104003)Natural Science Foundation in Shanghai(No.21ZR1424200)。
文摘Due to its high operational voltage and energy density,P2-type Na_(0.67)Ni_(0.3)Mn_(0.7)O_(2) has become a leading cathode material for sodium-ion batteries(SIBs),which is an ideal option for large-scale energy storage.However,the practical application of P2-type Na_(0.67)Ni_(0.3)Mn_(0.7)O_(2) is limited by the capacity constraints and unwanted phase transitions,presenting significant challenges to the widespread application of SIBs.To address these challenges and optimize the electrochemical properties of the P2 phase cathode material,this study proposes a Cu and Zn co-doped strategy to improve the electrochemical performance.The incorporation of Cu/Zn can stabilize the P2-phase structure against P2-O2 phase transitions,thus enhancing its electrochemical properties.The as-obtained P2-type Na0.67[Ni_(0.3)Mn_(0.58)Cu_(0.09)Zn_(0.03)]O_(2) cathode material shows an impressive cycling stability,maintaining 80%capacity retention after 1000 cycles at 2 C.The cyclic voltammetry(CV)tests show that the Cu^(2+)/Cu^(3+)redox reaction is also involved in charge compensation during the charge/discharge process.
