The first capacity of SZSN's silicon-based negative electrode material was 1616.3mAh / g, and the first efficiency was 76.89%. The capacity and efficiency were very close to commercial products.
In terms of the current lithium ion battery material system, the anode material is mainly graphite, but the silicon carbon anode material is considered to be the key to the industrialization of the next generation of high specific energy power batteries.
From the perspective of the market, China mainly uses nano-silicon-carbon composites and porous silicon-carbon composites. At present, only a few companies at home and abroad can achieve mass production of silicon-carbon, but there is still a large volume expansion problem in large-scale applications.
On December 21, the “Li Yuanheng · 2018 Senior Engineer Lithium Battery & Electric Vehicles Annual Conference” continued wonderfully at the Venus Royal Hotel in Shenzhen. As the annual event with the largest scale and highest participation in the lithium battery and electric vehicle industry, the site attracted more than 800 senior executives from the entire new energy vehicle industry chain of materials, equipment, batteries, BMS, PACK, complete vehicles, and operating leases.
In the material special title of Indole, SZSN R & D Director Hu Wenliang delivered a keynote speech on "Next Generation Lithium-Ion Battery Anode Materials: Silicon-Based Anodes", analyzing current Snow and domestic and international The latest development progress.
Hu Wenliang pointed out that at present, the main problems of silicon-based anode materials include volume expansion, pulverization of materials, failure of conductive networks, and repeated growth of SEI. The above problems may cause problems such as poor battery safety performance and poor rate performance. In this regard, we believe that the future development of silicon-based anodes mainly includes surface coating, special structures on the surface, pre-lithiation, compact structures, and matching of electrode systems.
Hu Wenliang said that the development direction of silicon-based anodes is mainly to reduce expansion, improve cycle life, and reduce production costs.
The measures to reduce expansion mainly include the structural design of materials, the cross-combination of multiple structures, multiple materials, and multiple technologies; the measures to improve life expectancy include nano-crystallization and in-situ coating; the cost reduction is mainly to innovate product processes, equipment and engineering Research and development, reducing production energy consumption.
Because the silicon-based negative electrode has a large volume expansion, it cannot be used directly, and it needs to be modified before it can be practically used. The main modification methods are structural modification, carbon coating modification and pre-intercalation of lithium.
Specifically, structural modification is to make materials into nanoparticles, nanowires, and nanosheets. This can improve the structural stability of the material, cushion the volume expansion of the material, and increase the active interface of the material, which is beneficial to the electrical properties of the material. Chemical properties.
Carbon coating is to coat a layer of carbon elements on the material. Carbon coating can suppress the volume expansion of the material, which is beneficial to the formation of a stable SEI film on the surface of the material. At the same time, carbon coating can improve the conductivity of the material, which is beneficial to the rate performance.
The pre-intercalation of lithium can form a layer of SEI on the surface of the electrode in advance, which reduces the first irreversible capacity loss and improves the electrode's first coulomb efficiency.
Hu Wenliang said that the first capacity of SZSN's silicon-based anode material was 1616.3mAh / g, and the first efficiency was 76.89%, which was very close to commercial products in terms of capacity and efficiency. The above data are half-battery data, and the application of full-battery is still being verified.
At the same time, Hu Wenliang also mentioned that due to the unique physical and chemical properties of silicon-based anodes, the current electrode system of graphite electrodes cannot meet the practical application of silicon-based materials, so new electrode systems need to be developed. For example, the use of new PAI binders and new electrolyte additives such as VC and FEC.
In terms of the influence of the binder on the material application, the binder should have high electrical conductivity and mechanical ductility, so as to effectively adapt to the large volume change of the silicon carbon anode during the cycle, in order to maintain high structural integrity. At the same time, the electrodes are highly conductive. The high modulus binder is beneficial to the cycling performance of the material.
In terms of the effect of the conductive agent on the application of the material, the conductive agent needs to have good conductive properties, and also needs a large aspect ratio, to form a three-dimensional conductive network in the electrode system, and the active material will not interact with the conductive agent during the cycle. Detachment occurs, keeping the electrode highly conductive.
The conductive agent in the form of dot-line composite can meet the short-range and long-range electron transmission channels, which is conducive to the performance of silicon-based cycling, and can effectively promote the capacity and improve the magnification.
In terms of the influence of the electrolyte on the material application, due to the large volume change of the silicon-based material during the cycle, the SEI film on the surface of the material will continue to weaken, grow, and consume lithium ions, which will cause the cycle performance of the material to decrease. The FEC additive has priority over the electrolyte solvent. It can form a compact SEI layer with excellent lithium conductivity at the negative electrode. A high content of FEC additive can effectively improve performance.