中间相炭微球在锂离子电池负极材料的应用进展

中间相炭微球(MCMB)具有良好锂离子扩散性、导电性和机械稳定性等优势,是目前应用广泛、综合性能优异的锂离子电池负极材料,但较低理论比容量是制约其发展的关键因素。为了获得性能优良的MCMB基锂离子电池负极材料,改性修饰和复合材料已然成为目前研发重点。笔者论述了碳结构、表界面和复合材料等微观结构设计对MCMB负极材料电化学性能的影响。从碳堆积结构类型、有序性、层间距以及球体粒径大小等方面,论述了碳结构微观设计对MCMB电化学性能的影响。发现具有乱层结构的MCMB在充放电过程中内部产生应力较小,且碳结构较稳定,具有优异循环稳定性;内部具有大量微孔或碳层间距较大的MCMB,在充放电过程中可提高锂离子在电极中的迁移速率,并提供更多的储锂空间,一般具有优良的充放电比容量和倍率性能;小粒径MCMB具有较短的锂离子迁移路径和随之增加的比表面积,通常具有较好倍率性能,伴随着可逆比容量和充放电效率的衰减。从表界面碳层改性、包覆和掺杂改性等方面,论述了表界面改性对MCMB电化学性能的影响。表面碳层修饰可增加MCMB与电解液的相容性及其比表面积,提高了与电解液的接触面积及贮锂容量,改善了锂离子电池负极材料的电化学性能;另外,MCMB表面包覆一层无定型碳,可避免其表面与电解液直接接触,减少电化学副反应的产生,提升其可逆比容量。从碳活性物质复合材料、非碳活性物质复合材料等方面,论述了复合材料微观结构设计对MCMB电化学性能的影响。碳活性物质可降低MCMB内部碳层结构的有序性,减少锂离子嵌入过程中的内部应力,提升MCMB循环稳定性。非碳活性物质诱导MCMB生成更加有序的碳层结构,提高MCMB的比表面积,从而改善MCMB表面与电解液分子的接触能力及其嵌锂性能,有利于提升MCMB负极材料可逆比容量、循环性能和倍率性能。MCMB具有高碳层间距和多缺陷位点等结构特征,有利于钠离子自由脱嵌,应用于钠离子电池时具有良好的可逆比容量、循环稳定性和倍率性能。MCMB的不规则定向层状结构经活化等处理具有较高比表面积,可应用于超级电容器电极材料。最后提出在高性能锂离子电池电极材料快速发展的需求下,从微观结构角度设计MCMB纳米复合材料将是MCMB负极材料的研究重点。

Application progress on mesocarbon microbeads as anode materials for lithium ion batteries

MCMB has the advantages of good lithium ion dispersion,conductivity and mechanical stability,which is a widely used anode material of lithium ion battery with excellent comprehensive performance. However,the low theoretical specific capacity is a key factor for restricting its development. In order to obtain MCMB based anode materials with excellent performance,the modification of MCMB and its composite materials have become the focus of current research and development. So,the effect of microstructure design on electrochemical properties of MCMB lithium-ion battery anode materials was discussed,such as carbon structure,surface interface and composite materials.The influence of carbon structure microstructure design on the electrochemical performance of MCMB was discussed from the aspects of carbon stacking structure type,carbon layer order,carbon layer interlayer spacing and sphere particle size. It is concluded that MCMB with a disordered layer structure generates less internal stress during charging and discharging,and the carbon structure is relatively stable,thereby it has excellent cycle stability. MCMB with a large number of micropores or a large carbon layer spacing,can increase the migration rate of lithium ions in the electrode and provide more lithium storage space during charging and discharging,which often shows excellent charge and discharge specific capacity and rate performance. MCMB with the small particle size has a shorter lithium ion migration path,but the specific surface area of the electrode material will also increase accordingly,which show better rate performance and relatively poor reversible specific capacity and the attenuation of charge discharge efficiency.The influence of surface interface carbon layer modification on the electrochemical properties of MCMB was discussed from the aspects of surface interface modification,coating and doping modification. The literature indicates that the surface carbon layer modification can increase the electrolyte compatibility specific surface area of MCMB with electrolyte,promote the contact area of electrolyte and the lithium storage capacity,and improve the electrochemical performance of lithium ion battery anode materials. In addition,the MCMB surface coating a layer of amorphous carbon can avoid direct contact between its surface and the electrolyte,reduce the electrochemical side reactions and increase the reversible specific capacity. From the aspects of carbon active material composites and non-carbon active material composites,the influence of the microstructure design of the composite materials on the electrochemical performance of MCMB was discussed. The carbon active material can decrease the carbon layer structure order inside the MCMB,which can reduce the internal stress caused by the lithium ion insertion process and improve the cycle stability. Non-carbon active materials can induce MCMB to form a more ordered carbon layer structure and increase its specific surface area,improve the contact ability and the lithium insertion performance between MCMB surface and electrolyte molecules,which is conducive to improving the reversible specific capacity,cycling performance and rate performance of MCMB anode. MCMB possesses the specially structural characteristics,such as the high carbon layer spacing and the multiple defect sites,which is also conducive to the free extraction of sodium ions. When MCMB is applied to sodium ion batteries,it often shows good reversible specific capacity,cycle stability,and rate performance. Similarly,the irregularly oriented layered structure of MCMB has a high specific surface area after activation,so MCMB can be applied to the electrode materials of supercapacitors. Finally,the application of MCMB as lithium ion battery anode materials was prospected. With the development of high-performance lithium ion battery electrode materials,the research focus of MCMB anode materials would be to design the MCMB nanocomposite materials from the perspective of microstructure.