Uncovering the solid-phase conversion mechanism via a new range of organosulfur polymer composite cathodes for lithium-sulfur batteries

The sulfur cathodes operating via solid phase conversion of sulfur have natural advantages in suppressing polysulfide dissolution and lowering the electrolyte dosage,and thus realizing significant improvements in both cycle life and energy density.To realize an ideal solid-phase conversion of sulfur,a deep understanding of the regulation path of reaction mechanism and a corresponding intentional material and/or cathode design are highly essential.Herein,via covalently fixing of sulfur onto the triallyl isocyanurate,a series of S-triallyl isocyanurate organosulfur polymer composites(STIs) are developed.Relationship between the structure and the electrochemical conversion behavior of STIs is systematically investigated.It is found that the structure of STIs varies with the synthetic temperature,and correspondingly the electrochemical redox of sulfur can be controlled from conventional "solid-liquid-solid" conversion to the "solid-solid" one.Among the STI series,the STI-5 composite realizes an ideal solid-phase conversion and demonstrates great potential for building a Li-S battery with high-energy density and long-cyclelife:it realizes stable cycling over 1000 cycles in carbonate electrolyte,with a degradation rate of0.053% per cycle;the corresponding pouch cell shows almost no capacity decay for 125 cycles under the conditions of high sulfur loading(4.5 mg cm^(-2)) and lean electrolyte(8 μL mg_s^(-1)).In addition,the tailoring strategy of STI can also apply to other precursors with allyl functional groups to develop new organosulfur polymers for "solid-solid" sulfur cathodes.The vulcanized triallyl phosphate(STP) and triallylamine(STA) both show great lithium storage potential.This strategy successfully develops a new family of organosulfur polymers as cathodes for Li-S batteries via solid-phase conversion of sulfur,and brings insights to the mechanism study in Li-S batteries.

Post-Synthetic and In Situ Vacancy Repairing of Iron Hexacyanoferrate Toward Highly Stable Cathodes for Sodium-Ion Batteries

Iron hexacyanoferrate(FeHCF)is a promising cathode material for sodium-ion batteries.However,FeHCF always suffers from a poor cycling stability,which is closely related to the abundant vacancy defects in its framework.Herein,post-synthetic and in-situ vacancy repairing strategies are proposed for the synthesis of highquality FeHCF in a highly concentrated Na_(4)Fe(CN)_(6) solution.Both the post-synthetic and in-situ vacancy repaired FeHCF products(FeHCF-P and FeHCF-I)show the significant decrease in the number of vacancy defects and the reinforced structure,which can suppress the side reactions and activate the capacity from low-spin Fe in FeHCF.In particular,FeHCF-P delivers a reversible discharge capacity of 131 mAh g^(−1) at 1 C and remains 109 mAh g^(−1) after 500 cycles,with a capacity retention of 83%.FeHCF-I can deliver a high discharge capacity of 158.5 mAh g^(−1) at 1 C.Even at 10 C,the FeHCF-I electrode still maintains a discharge specific capacity of 103 mAh g^(−1) and retains 75% after 800 cycles.This work provides a new vacancy repairing strategy for the solution synthesis of high-quality FeHCF.

Facile synthesis of sulfurized polyacrylonitrile composite as cathode for high-rate lithium-sulfur batteries

Sulfurized polyacrylonitrile(SPAN)as a promising cathode material for lithium sulfur(Li-S)batteries has drawn increasing attention for its improved electrochemical performance in carbonate-based electrolyte.However,the relatively poor electronic and ionic conductivities of SPAN limit its high-rate and lowtemperature performances.In this work,a novel one-dimensional nanofiber SPAN(SFPAN)composite is developed as the cathode material for Li-S batteries.Benefitting from its one-dimensional nanostructure,the SFPAN composite cathode provides fast channels for the migration of ions and electronics,thus effectively improving its electrochemical performance at high rates and low temperature.As a result,the SFPAN maintains a high reversible specific capacity^1200 mAh g−1 after 400 cycles at 0.3 A g−1 and can deliver a high capacity of^850 mAh g−1 even at a high current density of 12.5 A g−1.What is more,the SFPAN can achieve a capacity of^800 mAh g−1 at 0℃and^1550 mAh g−1 at 60℃,thus providing a wider temperature range of applications.This work provides new perspectives on the cathode design for high-rate lithium-sulfur batteries.

利用简单硫化处理的铜箔获取稳定的金属锂负极

金属锂被认为是下一代高能量密度二次电池的终极形式.但是,金属锂的高活性和枝晶生长严重限制了其商业化应用.只有实现锂离子的均匀沉积才能解决相关问题.本研究通过对商业化铜箔进行简单的一步法硫化处理,在其表面原位生成一层具有亲锂性的Cu2S修饰层.该Cu2S层不仅可以利用其亲锂性促进锂离子的均匀沉积,而且在初始活化过程中有利于形成稳定的固态电解质界面.在锂沉积/剥离循环过程中,这种经过修饰的铜箔集流体有效抑制了锂枝晶生长,即使在4 mA h cm^-2的循环条件下,也能够展现出较高的库仑效率和稳定的循环性能.将沉积金属锂后的Cu2S/Cu-Li复合负极与Li Fe PO4正极组装成全电池,其循环稳定性和库仑效率均大幅度提高,表明该修饰后的铜箔在二次金属锂电池领域具有良好的应用前景.

利用Cu_(3)N改性铜箔集流体提高锂金属负极的循环稳定性

在二次电池的所有固态负极中,锂金属负极因其极高的理论比容量和极低的还原电位对促进二次电池的进一步发展具有很大的潜力.然而,锂负极在不断脱锂/嵌锂的过程中因锂枝晶的生长导致低库伦效率并存在安全隐患,严重阻碍了锂金属负极的实际应用.该研究通过化学方法在商业化的铜箔集流体表面原位修饰Cu_(3)N纳米线得到复合微结构型集流体(Cu_(3)N NWs/Cu).引入的Cu_(3)N纳米线具有三维结构,不仅可以增大集流体的比表面积、降低集流体表面的电流密度,还可以容纳锂负极在沉积/脱嵌过程中发生的体积变化.此外,在首次锂沉积的过程中,Cu_(3)N与锂金属反应生成Li_(3)N(3Li+Cu_(3)N→Li_(3)N+3Cu),可以促进稳定的富含Li_(3)N的固态电解质膜(SEI)形成.富含Li_(3)N的SEI既能增强锂离子的传输,又能给锂的沉积提供充足的形核位点,促进锂金属的均匀沉积,从而抑制了锂枝晶的生长.在锂沉积/剥离循环过程中,这种经过Cu_(3)N纳米线修饰的铜箔集流体在电流密度为1 mA cm^(-2),锂沉积量为1 mA h cm^(-2)的条件下可以稳定循环270圈,平均库伦效率为98.6%.将沉积锂金属后的Cu_(3)N NWs/Cu-Li复合负极与LiFePO_(4)正极(正极活性物质载量:10 mg cm^(-2);N/P=2.35)组装成全电池,该全电池能稳定循环430圈.研究表明经Cu_(3)N纳米线修饰的铜箔集流体在提高锂金属负极的循环稳定性方面具有良好的应用前景.