Dual modification of LiNi_(0.83)Co_(0.11)Mn_(0.06)O_(2) cathode materials by K^(+) doping and Li_(3)PO_(4) coating for lithium ions batteries

Li_(3)PO_(4)@Li_(0.99)K_(0.01)Ni_(0.83)Co_(0.11)Mn_(O.06)O_(2)(NCM-KP) cathode powders are synthesized via K^(+)doping in calcination processes and H_3PO_4 coating in sol-gel processes.K^(+) precisely enters into the lattice to widen the(003) plane to 0.4746 nm with a lower cationic disordered degree of 1.87%.Moreover,the surface residual lithium salts are treated by H_3PO_4 to generate a uniform Li_(3)PO_(4) coating layer of approximately 11.41 nm,which completely covers on the surface of secondary spherical particles to improve the interfacial stability.At 25℃,the NCM-KP electrode delivers a discharge specific capacity of 148.9 mAh·g^(-1) with a remarkable capacity retention ratio of 84.1% after 200 cycles at 1.0C and retains a high reversible specific capacity of 154.4 mAh·g^(-1) at 5.0C.Even at 1.0C and 60℃,it can maintain a reversible discharge specific capacity of 114.6 mAh·g^(-1) with 0.21% of capacity decay per cycle after 200 cycles,which is significantly lower than 0.40% for the pristine NCM powders.Importantly,the charge transfer resistance of 238.89 Ω for the NCM-KP electrode is significantly lower than 947.41 Ω for the pristine NCM one by restricting the interfacial side reactions.Therefore,combining K+doping and Li_(3)PO_(4) coating is an effective strategy to enable the significant improvement of the electrochemical property of high-nickel cathode materials,which may be mainly attributed to the widened diffusion pathway and the formed Li_(3)PO_(4) protective layer,thus promoting Li~+diffusion rate and preventing the erosion of HF.

Stabilization of high-voltage layered oxide cathode by utilizing residual lithium to form NASICON-type nanoscale functional coating

High-voltage medium-nickel low-cobalt lithium layered oxide cathode materials are becoming a popular development route for high-energy lithium-ion batteries due to their relatively high capacity,low cost,and improved safety.Unfortunately,capacity fading derived from surface lithium residue,electrode-electrolyte interfacial side reactions,and bulk structure degradation severely limits large-scale commercial utilization.In this work,an ultrathin and uniform NASICON-type Li_(3)V_(2)(PO_(4))_(3)(LVP)nanoscale functional coating is formed in situ by utilizing residual lithium to enhance the lithium storage performance of LiNi_(0.6)Co0.05Mn_(0.35)O_(2)(NCM)cathode.The GITT and ex-situ EIS and XPS demonstrate exceptional Li+diffusion and conductivity and attenuated interfacial side reactions,improving the electrode-electrolyte interface stability.The variable temperature in-situ XRD demonstrates delayed phase transition temperature to improve thermal stability.The battery in-situ XRD displays the singlephase H1-H2 reaction and weakened harmful H3 phase transition,minimizing the bulk mechanical degradation.These improvements are attributed to the removal of surface residual lithium and the formation of NASICON-type Li_(3)V_(2)(PO_(4))_(3)functional coatings with stable structure and high ionic and electronic conductivity.Consequently,the obtained NCM@LVP delivers a higher capacity retention rate(97.1%vs.79.6%)after 150 cycles and a superior rate capacity(87 mAh·g^(-1)vs.58 mAh·g^(-1))at a 5 C current density than the pristine NCM under a high cut-off voltage of 4.5 V.This work suggests a clever way to utilize residual lithium to form functional coatings in situ to improve the lithium storage performance of high-voltage medium-nickel low-cobalt cathode materials.

Simultaneously enhanced electrochemical performance and air stability of Ni-rich cathode with a modified washing process

Water washing has been regarded as one of the most effective strategies to remove surface residual lithium of nickel-rich layered oxides for lithium-ion batteries(LIBs).However,the loss of lattice lithium during the water washing process deteriorates the electrochemical performances and air stability.Herein,washing the LiNi_(0.90)Co_(0.05)Al_(0.02)O_(2)(NCA) with ammonium dihydrogen phosphate(NH_(4)H_(2)PO_(4)) solution has been proposed to simultaneously enhance electrochemical performances and air stability,in which in-situ generated Li_(3)PO_(4) coating layer on surface of NCA can suppress the loss of lattice lithium.Besides,as a fast ionic conductor,Li_(3)PO_(4) coating layer on NCA can prevent the direct contact with electrolyte/air.As a result,the NH_(4)H_(2)PO_(4) solution washed NCA cathode can deliver a high capacity of131.9 mAh·g^(-1) at 10.0C rate as well as impressive cycle stability with a capacity retention of 83.1% after 100 cycles at 1.0C,much higher than those of water washed NCA(WS-NCA) electrode.After exposed in air for 7 days,the NH_(4)H_(2)PO_(4) solution washed NCA electrode can more effectively maintain the structural integrity as well as the electrochemical performances than water-washed NCA.This work provides a simple and effective approach to enhance the cycle stability and air stability of Nickel-rich cathode materials.

Strategies of Removing Residual Lithium Compounds on the Surface of Ni-Rich Cathode Materials

Ni-rich cathode materials have become one of the most promising cathode materials for advanced high-energy Li-ion batteries(LIBs)owing to their high specific capacity.However,Ni-rich cathode materials are sensitive to the trace H2O and CO2 in the air,and tend to react with them to generate LiOH and Li2COg at the particle surface region(named residual lithium compounds,labeled as RLCs).The RLCs will deteriorate the comprehensive performances of Ni-rich cathode materials and make trouble in the subsequent manufacturing process of electrode,including causing low initial coulombic efficiency and poor storage property,bringing about potential safety hazards,and gelatinizing the electrode slurry.Therefore,it is of considerable significance to remove the RLCs.Researchers have done a lot of work on the corresponding field,such as exploring the formation mechanism and elimination methods.This paper investigates the origin of the surface residual lithium compounds on Ni-rich cathode materials,analyzes their adverse effects on the per-formance and the subsequent electrode production process,and summarizes various kinds of feasible methods for removing the RLCS.Finally,we propose a new research direction of eliminating the lithium residuals after comparing and summing up the above.We hope this work can provide a reference for alleviating the adverse effects of residual lithium compounds for Ni-rich cathode materials'industrial production.