Lithium titanate batteries consist of positive and negative plates (triode lithium for positive active materials, lithium titanate for negative electrodes), separators, electrolytes, tabs, and stainless steel (aluminum alloy) housings. The positive and negative plates are the areas of electrochemical reaction. The diaphragm and the electrolyte provide Li+ transmission channels, and the tabs serve to guide the current.
When the battery is charged, Li+ migrates from the ternary Lithium material to the surface of the crystal, and is released from the positive electrode plate material. Under the action of the electric field force, the electrolyte enters the electrolyte, passes through the separator, and then migrates through the electrolyte to the lithium titanate crystal of the negative electrode. The surface is then embedded in the negative lithium titanate spinel structure material. At the same time, electrons flow through the aluminum foil of the positive electrode, through the tabs, battery posts, loads, negative pole posts, and negative electrode ear currents to the aluminum foil electrodes of the negative electrode, and then flow through the conductors to the lithium titanate negative electrode, so that the charge is balanced.
When the battery is discharged, Li+ is deintercalated from the lithium titanate spinel structural material, enters the electrolyte, passes through the separator, migrates through the electrolyte to the surface of the ternary lithium crystal, and is then re-embedded into the ternary lithium material. At the same time, the aluminum foil electrode, which flows through the conductor to the negative electrode through the conductor, flows through the tab, the negative pole of the battery, the load, the positive pole, and the positive pole tab to the aluminum foil electrode of the battery positive pole, and then flows through the conductor to the trivalent lithium positive pole. Bring the charge up to balance.
Thus, the basic principle of lithium titanate battery is that during the charging and discharging process, the corresponding lithium ions insert back and forth between the positive and negative electrodes to complete the charge and discharge of the battery and the power supply to the load. Lithium titanate battery charge and discharge diagram as shown.
When the battery is charged, the positive electrode loses electrons, and lithium ions are released and embedded in the negative electrode. When the negative electrode is intercalated with lithium ions, the electrons become lithium-rich at the same time. The process is exactly the opposite when it is discharged. During the reaction of Li+ intercalation or deintercalation, lithium titanate (Li4TI5O12) is an ideal embedded electrode material. Li+ insertion and deintercalation have almost no influence on the material structure, so it is called "zero-strain" material. Ensure its good cycle performance.
Lithium titanate has two different phases of molecular structure - Li7TI5O12 and Li4TI5O12. Both the crystal structure of Li7Ti5O12 and the crystal structure of Li4Ti5O12 are spinel structures with little change in lattice constant and small volume change. It can avoid the collapse of the structure of the electrode material during the charge-discharge cycle, so as to improve the cycle performance and service life of the electrode, reduce the attenuation of the capacity with the increase of the number of cycles, so that lithium titanate has excellent cycle performance. .
The electrochemical reaction equation of lithium titanate battery:
The total chemical reaction equation:
Lithium titanate battery structure composition：
Positive electrode: lithium iron phosphate, lithium manganate or ternary material, lithium nickel manganese oxide.
Negative electrode: Lithium titanate material.
Diaphragm: Lithium battery separator with carbon as negative electrode.
Electrolyte: Lithium battery electrolyte with carbon as anode.
Battery case: Lithium battery case with carbon as negative electrode.
Lithium titanate battery’advantages
Lithium titanate battery has small size, light weight, high energy density, good sealing performance, no leakage, no memory effect, low self-discharge rate, rapid charge and discharge, long cycle life, wide operating temperature range, safety and stability, and environmental protection Such characteristics, so it has a very wide range of application prospects in the field of communications power.
When lithium titanate is used as a negative electrode material, the potential plateau is as high as 1.55 V, which is more than 1 V higher than the conventional graphite negative electrode material. Although some energy density is lost, it also means that the battery is more safe. Lu Blu-ray, a technical expert, once stated that when the battery is rapidly charged, the voltage requirement for the negative electrode is relatively low, but if it is too low, the lithium battery can easily precipitate very active metallic lithium. This lithium ion not only conducts electricity, but also reacts with the electrolyte, and then Releases heat, produces combustible gases, and causes fire. The lithium titanate prevents the negative voltage from being 0 due to the high 1V voltage, which indirectly avoids the precipitation of lithium ions, thus ensuring the safety of the battery.
Since lithium titanate batteries can be used safely in high-temperature and low-temperature environments, they also demonstrate their important advantages of wide temperature resistance (especially low temperature resistance). At present, the safe working temperature range of Lilong Lithium Titanate battery is between -50 degrees and 65 degrees, and the energy of ordinary graphite negative batteries begins to decay when the temperature is lower than -20 degrees, and the charging capacity is only -30 degrees. 14% of the total charging capacity does not work at all in cold weather. In addition, since the lithium titanate battery has an 1% volume change even if it is overcharged, it is called a zero-strain material, which gives it an extremely long life. Yin Longchang, chairman of Yinlong, once stated that the lifespan of Lilong Lithium Titanate battery can reach 30 years, which is equivalent to the service life of the car, while the average life span of ordinary graphite negative electrode materials is only 3-4 years. From the perspective of the entire life cycle, lithium titanate battery cost is lower.
The last advantage of lithium titanate is its rapid charge and discharge capability and its high charge rate. Currently, the charge rate of silver-silver titanate batteries is 10C or even 20C, while that of ordinary graphite anode materials is only 2C-4C. Based on these technical characteristics of lithium titanate batteries, the industry believes that it meets the needs of new energy buses and large-scale energy storage equipment.
Disadvantages of lithium titanate battery
The excellent safety performance makes the study of lithium titanate batteries become a hot spot, but the Li4Ti5O12 material itself has a low electron conductivity (10-13S/cm) and a lithium ion diffusion coefficient (10-10~10-13cm2/S). ) Greatly limited the application at high magnification. Some scholars have shown that after nano-particle size Li4Ti5O12 can expand the effective reaction area and reduce the diffusion distance, thereby significantly improve the material's rate performance. However, it should be pointed out that the process of nanocrystallization of material particles is often difficult and requires high costs. It is difficult to achieve large-scale industrial production at present.
Lithium titanate batteries will continue to produce gas during the cycle, causing the battery pack to bulge, especially at high temperatures, affecting the positive and negative electrode contact, increasing the battery impedance, affecting the performance of the battery. This is also one of the major obstacles to limiting the wide application of lithium titanate as a negative electrode material in batteries.
The difficulty of Lithium Titanate Battery Technology Development and Its Development Direction
1.Reasons for Developing Lithium Titanate Battery Technology in China
The competition of lithium titanate battery technology in China's various energy storage batteries should take advantage of time, location, and people. In terms of service life, the long cycle life of lithium titanate batteries is far better than that of lead-acid batteries of various types; its efficiency, cost, and electrochemical performance are even better than those of sodium and sulfur and liquid flow vanadium.
China’s population base accounts for about 1/5 of the world’s population. Due to its large population, China’s electric vehicle, energy storage, and industrial application market is a huge market that is being coveted by multinational companies in many countries. In recent years, the Chinese government has attached great importance to the development of electric vehicles and energy storage industries, and various national encouragement policies have been introduced. Lithium titanate battery systems made in China have accumulated commercial application data for several years in hybrid electric buses in Chongqing and Europe, demonstration storage stations in Zhangbei, and Shenzhen Baoqing Energy Storage Power Station.
In addition, the upstream and downstream industries of China's lithium battery industry have already become a climate, in addition to a complete battery material supply and equipment manufacturing capabilities, lithium battery production capacity is also Japan and South Korea three points. This has made China's lithium battery manufacturers have an inherent condition for the transition from traditional lithium production to lithium titanate battery production.
China has already had such powerful and experienced companies as Lithium Titanate, Sichuan Yinlong, Zhuhai Yinlong, and Huzhou Weihong. Representative companies that have emerged in the production of lithium titanate batteries include Huzhou Weihong, Zhuhai Yinlong, Shenzhen Boleida, and Tianjin Jiewei.
These companies have already established their own sales channels at home and abroad in the electric vehicle and energy storage market. In particular, it is worth pointing out that Shenzhen Boreda possesses a series of proprietary technologies and intellectual property rights ranging from material production to battery production and system integration. At present, China's lithium power industry is still a rare manufacturer with independent intellectual property rights.
2. The future development direction of lithium titanate technology
Finally, it is necessary to comprehensively summarize the advantages and disadvantages of lithium titanate as a lithium negative electrode. The advantages are: ultra-high safety, long life, high and low temperature range, high power, low cost, and environmental protection. Disadvantages: Lithium titanate material has low energy density, strong water absorption, high environmental requirements for battery production, corresponding updating of the production process, new process requires investment in necessary equipment and higher humidity control, and lithium titanate battery The application market has not yet fully opened.