Sodium Alginate Inhibits Cation Mixing In Lithium Ion Battery Cathode Materials

The performances of batteries are required to progress much more quickly to fit the increasing development of science and technology,the miniaturizaiotn of electronic equipment and instrument,and the fast development of modern military utilization and astronautical technology.In view of comprehensive properties,rechargeable lithium ion batteries(LIBs)area class ofhigh-performance batteries with greatdevelopmentpotentialand good application future.LiFePO4 is believed to been a very potential cathode material for LIBs due to the low cost,environmental friendliness,high specific capacity and high stability.However,Fe-Li antisite defect is afatal problem,which limits the lithium ion diffusion rate in the Li Fe PO4 paticles and reduces its rate performance.Meanwhile,Ni-rich Li(NixCoyMnz)O2(x ? 0.5)has become the research focus with its higher specific capacity and higher votage platform in recent yeas.However,the cation mixing of Ni and Li leads to the poor cycle stability and rate performance.Therefore,it is necessary to design an effective method to solve the cation mixing in the crysal structure of cathode materials of LIBs.The main purpose of this work is to find a unique method to surpress the cation mixing in the crysal structure of cathode materials of LIBs using the special structure in alginate macromolecules.For the purpose of perfectingthe crystal structure and improving the diffusion rate of lithium ion,specific energy and power density,we investigated the synthesis process of the cathode materials Li(NixCoyMnz)O2and LiFePO4,the optimization of crystalline structure,and the various factors to affectthe charge and discharge process of LIBs.We synthesized Ni-rich Li(NixCoyMnz)O2hollow fiber with low cation mixing using alginate fiber as template,in whichthe Mn+(M = Ni,Co,Mn)cations were first immobilized into a novel "egg-box" arrangement via coordination with negatively charged ?-L-guluronate(G)blocks of the linear alginate macromolecule.Meanwhile,the ?-D-mannuronate(M)blocks in alginate can absorb Li+ via the negatively charged carboxyl groups.This can suppress the cation mixing efficiently at the initial stage.The amount of Li and Ni disorder in the multi-shelled Li(NixCoyMnz)O2 hollow fibres we synthesized is as low as 0.0485 for x = 0.5.The low cation mixing results from the cationconfinement by the novel "egg-box" structure in the seaweed-derived sodium alginatetemplate.These Ni-rich Li(NixCoyMnz)O2 hollow fiber electrodesexhibit remarkably high rate performance(172.7 mAh g-1 at 2 A g-1 for x = 0.8),highly reversible capacities(229.9 mAh g-1 at 20 mA g-1 for x = 0.8),and excellent cycling stability(capacity retention of 84.36 % after 300 cycle)for LIBs,with the overall performance are superior to all the Ni-rich electrodes reported to date.This superior performancestems from thelow cation mixing and desirable multi-shelled hollow fibrous structure.We used a simple seaweed biomass conversion strategy towardsporous LiFePO4/carbon hybrid microtubes(LFP/CMTs)with very low Fe-Li antisite defects.The percentage of Fe-Li antisites in the LFP/CMTs we synthesized is as low as 0.23 % for LFP/CMT-750.The cationconfinement of the XRD patterns showed that the Fe3+ cation immobilized into a novel "egg-box" arrangement via coordination with negatively charged ?-L-guluronate(G)blocks of the linear alginate macromolecule and Li+ absorbed by the ?-D-mannuronate(M)blocks in alginate can efficiently control the prior occupancy of Fe at the beginning of the crystal formation.As the temperature increasing,the "egg-box" was converted to carbon/metal core/shell structure,which can still efficiently avoid the Fe-Li aggregation.Meanwhile,the carbon skeleton converted to porous carbon microtube under N2 atmosphere.These LFP/CMTelectrodesexhibit superior discharge capacity of 165 mAh g-1 at 0.5 C,excellent capacity retention of 91 % after 1000 cycle numbers,and outstanding rate capacity of 99.7 mAh g-1 at 100 C for LIBs,with the overall performance are superior to all theLFP/C electrodes reported to date.This superior performancestems from thelow Fe-Li antisites and desirablecarrier of highly porous carbonaceous hybrid microtube.We synthesized three-dimentional C@LFP/GA using sodium alginate.The single crystalline LiFePO4 nanosheets with very low Fe-Li antisite defects and a largepercentage of highly oriented [010] facets shorten the path of lithium ion diffusion.The as-obtained LFP provides the highest poredensity for lithium-ion insertion/extraction.As a consequent,the C@LFP/GA-10 displays superior discharge capacity of 163.6 mAh g-1 at 0.5 C,excellent capacity retention of 99.55 % after 2000 cycle numbersat 10 C,and outstanding rate capacity of 101.6 m Ah g-1 at 100 C.A full cell with C@LFP/GA as cathode electrode and Li4Ti5O12 as anode electrode achievs remarkable specific energy and power density values of 265 Wh kg-1and 6.81 kW kg-1,respectively.This superior performancestems from the structure of LFP nanosheet with large [010] surfaces and 3D porous graphite conductive network.