Recently, a seminar on lithium titanate batteries closed in Wuxi. The industry's enthusiasm for lithium titanate is beyond imagination. The guests at the conference conducted thorough and in-depth discussions on a number of topics, and the participants expressed that they have benefited a lot. The author sorted out the speech content of many speakers, from which we can get a glimpse of the current status of lithium titanate battery technology development and the industry's views on key issues.
The latest progress in the performance research of lithium titanate batteries
Energy storage is considered to be the next outlet for new energy, and the application of lithium titanate batteries in the field of energy storage is highly expected. Lai Xiaokang, Dean of China Electric Power Research Institute, shared in the report his team's research and application experience in lithium titanate energy storage battery reconstruction technology, evaluation technology, and system application technology. They found through research that the life of lithium titanate batteries is greatly affected by the calendar time. At present, cycle life and accelerated aging are mainly carried out. Next, it is necessary to find the relationship between calendar time and accelerated aging, optimize the existing electrochemical model, and the future The combination of more refined boundary conditions improves the accuracy of the accelerated evaluation method for lithium-ion energy storage batteries.
Faster charging speed and longer service life are people's constant expectations for power batteries. Liu Wenjuan, vice president of technology of Weihong Power System (Huzhou) Co., Ltd. (hereinafter referred to as "Weihong Power"), introduced the company's power battery research and development progress. The product roadmap of Weihong Power shows that the battery technology developed by the company has undergone the evolution of "LPTO-LPCO-MPCO". Among them, the charging rate of the LPTO battery reaches 6C and the cycle life reaches 25,000 times; the energy density of the LPCO battery is 120~140Wh/kg, The charging rate is 4C, the cycle life is more than 10,000 times, and it can be started at -30℃; the MPCO battery developed in 2017 has a mass-energy density of 170Wh/kg, a volume energy density of 300Wh/L, and a charging rate of 4C With a cycle life of more than 7000 times, this battery cell has been planned to be loaded on a taxi.
Tianjin Gateway Power Industry Co., Ltd. (hereinafter referred to as “Gateway Power”) has launched research and development for the 48Ah high-energy lithium titanate battery. At present, the product has an energy density of 115Wh/kg under the condition of 1C charging; under the condition of 6C, constant current charging The input ratio reached 84%, the 6C discharge capacity retention rate reached 95%, and the -20°C discharge capacity retention rate reached 77%. Wang Chiweenie, Technical Director of Gateway Power, said that the company expects to complete the development of 120Wh/kg products by the end of 2017. For lithium titanate batteries, this energy density is really not low, which also caused heated discussions at the meeting.
The team of Professor Tang Zhiyuan from the Department of Applied Chemistry, School of Chemical Engineering and Technology, Tianjin University developed a cylindrical ultra-large-capacity monomer 400Ah lithium titanate/lithium iron phosphate battery. For the first time, the battery uses lithium iron phosphate with good thermal stability as the positive electrode material, and "zero strain" lithium titanate as the negative electrode material. Starting from the design of the internal structure of the power battery, it solves the problem of internal heat dissipation, current density distribution, and battery oversize. The contradictory relationship between capacity and high power ensures the safety and cycle life of the battery (more than 800 times). In addition, the team designed a novel stainless steel casing, which has a lower cost, and the battery has strong practical performance such as pressure resistance and impact resistance. It is understood that the project has obtained more than ten authorized national invention patents. In addition to civilian use, it has a wide range of industrial application prospects in aerospace, military, and other fields.
Lithium titanate battery material innovation
Titanium-based anode material: Professor Xia Yongyao's team from the New Energy Research Institute of the Department of Chemistry, Fudan University has developed a new type of lithium-ion battery anode material-Li2TiSi5. This titanium-based anode material fills the existing carbon for commercial lithium-ion batteries The gap with lithium titanate anode materials has certain application prospects.
Although the "zero strain" material Li4Ti5O12 avoids the problem of graphite anode dendrites, its lower theoretical capacity (160mAh/g) and high lithium insertion potential (1.5V relative to metal lithium) cause battery energy The density is low. In order to ensure the safety and high energy density of the battery, the development of a new anode material with a relatively large capacity and a lithium-intercalation potential lower than 1V but not close to the Li deposition potential has become a top priority. The new titanium-based anode material Li2TiSiO5 developed by the scientific research team of Professor Yongyao Xia not only has a large capacity (308mA/g), but also has a relatively low lithium insertion potential (about 0.28V, vs. Li+/Li). The further development of batteries is of great significance.
High-performance micro-nano anode materials: Shenzhen Beterui New Energy Materials Co., Ltd. (hereinafter referred to as "Betterui") has developed lithium titanate products earlier. The structure of the second generation product (LTO-2S) optimizes the void distribution and adopts a spherical design, which is beneficial to improve the vibration and compaction. This micro-nano anode material is mainly used in "Super Electric" and has been successfully mass-produced in 2016. According to Battery China.com, BTR's third-generation product (LTO-3S) began research and development in 2017.
Graphene composite lithium titanate anode material: Aiming at the problems of poor conductivity of lithium titanate batteries, low lithium diffusion coefficient, and low energy density, Tianjin Pulan Energy Technology Co., Ltd. has developed graphene composite lithium titanate anode materials. The negative electrode battery has good safety, long cycle life, small volume strain, and a high SOC utilization rate.
Modified lithium titanate materials: Shandong Yuhuang New Energy Technology Co., Ltd. has developed modified lithium titanate materials for the manufacture of high-performance batteries. The company improves electronic conductivity through carbon-nitrogen conductive layer modification and ion doping; through surface modification of nano-oxide/nitride to increase specific capacity. In terms of cycling, the specific capacity under 1C state is 174.2mAh/g, and the capacity retention rate is 90.4% for 1100 cycles; in terms of rate, the specific capacity of 10C is about 120mAh/g; constant current 15C fast charge (about 3.5min), charge Enter about 90% of the rated capacity.
Discussion on Gas Production
Guo Chuntai, chairman of Tianjin Gateway Power Industry Co., Ltd., said that lithium titanate batteries have several major problems: low energy density, difficult manufacturing, and high cost. Among them, gas production is an old and difficult problem in the manufacturing and use of lithium titanate batteries. If it is not well controlled, it will affect the safety performance of the battery to a certain extent.
As for the cause of gas production, Associate Professor He Yanbing of Shenzhen Graduate School of Tsinghua University believes that the intrinsic interface reaction between lithium titanate and electrolyte solvent is the main reason for battery gas production. The main gases produced are hydrogen, carbon monoxide, and carbon dioxide.
So, how do we view the gas production of lithium titanate batteries? Fan Weifeng, a researcher at the Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, is more optimistic. He regards whether the gas production problem affects the application of power batteries as a criterion for judgment. For example, he said that power batteries with a cycle number of less than 10,000 are not affected by gas production; in production, some companies leave a small airbag on the soft pack battery to leave a space for the gas produced. Therefore, Fan Weifeng believes that the problem of gas production has almost no impact on lithium titanate batteries.
Zhan Shiying, manager of the research and development department of Yinlong New Energy Battery Research Institute, believes that the problem of gas production is a chemical problem that all lithium batteries have, and the key to its solution lies in materials and production processes.
The solution of He Yanbing’s team is to establish an insulation layer between the lithium titanate and the electrolyte interface (such as constructing a nano-carbon coating layer on the surface of lithium titanate), and the SEI film formed on the coordinated insulation layer can significantly inhibit lithium titanate/ The interface reaction of the electrolyte also improves the cycle stability of lithium titanate. They have specifically developed a flatulence-free nano-, sub-nano, and micro-scale lithium titanate material with dense structures that combine high density, high rate, and long cycle performance.
Weihong Power has improved the anode material of lithium titanate battery and adjusted the electrolyte formula and production process. Therefore, the soft package LPTO battery produced by Weihong Power has high safety; Gateway Power adopts high-potential and strong film-forming measures To solve the problem; Tianjin Pulan Energy Technology Co., Ltd.’s approach is also to reduce or block reactive sites.
In addition, with regard to gas production and safety issues, Lu Xuelong, a senior industry analyst at the Industrial Economics and Trends Research Center of the Taiwan Institute of Industrial Technology, believes that square batteries are safer than soft-pack batteries. Xu Jiayu, the chief scientist of Shandong Yuhuang New Energy Technology Co., Ltd., emphasized that battery safety is a systematic project, not just a matter of one or two materials. Although lithium titanate batteries have gas production problems, he still believes that lithium titanate batteries are currently the safest type of battery.
At the same time, some guests also expressed their opinions on the size of lithium titanate particles. Initially, the industry believed that the smaller the lithium titanate particles, the better, and their technical focus were on the refinement of lithium titanate particles. Later, through production practices, it was gradually discovered that the particles are not as small as possible: the finer particles may be More and more side reactions. This view has now become the consensus of the industry, and it also confirms the tortuous road of lithium titanate technology development.
The road ahead for lithium titanate batteries will still be bumpy, but the direction is always going forward. The efforts made by industry enterprises and research institutions on the development of lithium titanate battery technology will promote the continuous development of lithium titanate batteries.
