Understanding of the sodium storage mechanism in hard carbon anodes

Hard carbon has been regarded as the most promising anode material for sodiumion batteries(SIBs)due to its low cost,high reversible capacity,and low working potential.However,the uncertain sodium storage mechanism hinders the rational design and synthesis of high-performance hard carbon anode materials for practical SIBs.During the past decades,tremendous efforts have been put to stimulate the development of hard carbon materials.In this review,we discuss the recent progress of the study on the sodium storage mechanism of hard carbon anodes,and the effective strategies to improve their sodium storage performance have been summarized.It is anticipated that hard carbon anodes with high electrochemical properties will be inspired and fabricated for large-scale energy storage applications.

A polyethylene microsphere-coated separator with rapid thermal shutdown function for lithium-ion batteries

Thermal runaway is the main factor contributing to the unsafe behaviors of lithium-ion batteries(LIBs)in practical applications.The application of separators for the thermal shutdown has been proven as an effective approach to protecting LIBs from thermal runaway.In this work,we developed a thermal shutdown separator by coating a thin layer of low-density polyethylene microspheres(PM)onto a commercial porous polypropylene(PP)membrane and investigated the thermal response behaviors of the as-prepared PM/PP separator in LIBs.The structural and thermal analysis results revealed that the coated PM layer had a porous structure,which facilitated the occurrence of normal charge-discharge reactions at ambient temperature,although it could melt completely and fuse together within very short time periods:3 s at 110℃and 1 s at 120℃,to block off the pores of the PP substrate,thereby cutting off the ion transportation between the electrodes and interrupting the battery reaction.Consequently,the PM/PP separator exhibits very similar electrochemical performance to that of a conventional separator at ambient temperature.However,it performs a rapid thermal shutdown at an elevated temperature of^110℃,thus controlling the temperature rise and maintaining the cell in a safe status.Due to its synthetic simplicity and low cost,this separator shows promise for possible application in building safe LIBs.

Boosting rate and cycling performance of K-doped Na_(3)V_(2)(PO_(4))_(2)F_(3) cathode for high-energy-density sodium-ion batteries

As a promising cathode material,Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)has attracted wide attention for sodium-ion batteries(SIBs)because of its high operating voltage and high structural stability.However,the low intrinsic electronic conductivity and insufficient Na ion mobility of NVPF limit its development.Herein,K-doping NVPF is prepared through a facile ball-milling combined calcination method.The effects of K-doping on the crystal structure,kinetic properties and electrochemical performance are investigated.The results demonstrate that the Na_(2.90)K_(0.10)V_(2)(PO_(4))_(3)F_(3)(K0.10-NVPF)exhibits a high capacity(120.8 mAh g^(-1) at 0.1 C),high rate capability(66 mAh g^(-1) at 30 C)and excellent cycling performance(a capacity retention of 97.5%at 1 C over 500 cycles).Also,the occupation site of K ions in the lattice,electronic band structure and Na-ion transport kinetic property in K-doped NVPF are investigated by density functional theory(DFT)calculations,which reveals that the K-doped NVPF exhibits improved electronic and ionic conductivities,and located K^(+) ions in the lattice to contribute to high reversible capacity,rate capability and cycling stability.Therefore,the K-doped NVPF serves as a promising cathode material for high-energy and high-power SIBs.

揭示钠离子电池正极材料Na_(6-2x)Fe_(x)(SO_(4))_(3)(1.5≤x≤2.0)的结构及电化学性质

铁基硫酸盐聚阴离子材料因其成本低廉、电化学性能优异等优点,是钠离子电池大规模应用最有前景的候选材料之一.尽管Na_(2)Fe_(2)(SO_(4))_(3),Na_(2)Fe_(1.5)(SO_(4))_(3),Na_(2.4)Fe_(1.8)(SO_(4))_(3)和Na_(2.4)Fe_(1.8)(SO_(4))_(3)等Na_(6-2x)Fe_(x)(SO_(4))_(3)(NFSO-x 1.5≤x≤2.0)材料在储钠方面取得了巨大成果,但这些NFSO-x的相和结构特性仍存在争议,难以实现具有最佳电化学性能的纯相材料.本文通过实验方法和密度泛函理论计算研究了6个具有不同x的NFSO-x样品,以分析其相和结构特性.结果表明在NFSO-x的1.6≤x≤1.7区域存在纯相,部分Na离子倾向于占据Fe位点以形成更稳定的框架.NFSO-1.7在NFSO-x样品中表现出最佳的电化学性能,具有高的放电容量(0.1 C时为104.5 mAh g^(-1),接近其理论容量105 mAh g^(-1))、出色的倍率性能(30 C时为81.5 mAh g^(-1)),并在10,000次循环中具有超长的循环稳定性,容量保持率为72.4%.本研究有助于阐明铁基硫酸盐聚阴离子材料的相和结构特征,以促进其在大规模储能中的应用.

Amorphous NaVOPO_(4)as a High-Rate and Ultrastable Cathode Material for Sodium-Ion Batteries

The low cost and profusion of sodium resources make sodium-ion batteries(SIBs)a potential alternative to lithium-ion batteries for grid-scale energy storage applications.However,the use of conventional cathode materials for Na-ion intercalation/deintercalation cannot satisfy the requirements of high-powered and long lifespan performance due to multiphase transition and lattice confinement.