Introduction to the principle and composition of lithium titanate battery

Principle of lithium titanate battery

The lithium titanate battery is composed of a positive and negative electrode plate (the positive electrode active material is ternary lithium, the negative electrode is lithium titanate), a separator, an electrolyte, a tab, and a stainless steel (aluminum alloy) outer casing. The positive and negative plates are the areas of electrochemical reaction. The diaphragm and electrolyte provide a transmission channel for Li+, and the tabs act to guide the current.

When the battery is charged, Li+ migrates from the ternary lithium material to the crystal surface, and is separated from the positive electrode material. Under the action of the electric field force, it enters the electrolyte, passes through the separator, and then migrates to the negative lithium titanate crystal through the electrolyte. The surface is then embedded in a negative lithium titanate spinel structure material. At the same time, the electron flow passes through the aluminum foil of the positive electrode, and flows through the electrode, the battery pole, the load, the negative pole, the negative electrode to the aluminum foil electrode of the negative electrode, and then flows through the electric conductor to the lithium titanate negative electrode to balance the charge.

When the battery is discharged, Li+ is deintercalated from the lithium titanate spinel structure material, enters the electrolyte, passes through the separator, and then migrates to the surface of the ternary lithium crystal through the electrolyte, and then re-embeds into the ternary lithium material. At the same time, the electrons flow through the electrical conductor to the aluminum foil electrode of the negative electrode, and flow through the electrode, the negative electrode column, the load, the positive pole and the positive electrode to the aluminum foil electrode of the positive electrode of the battery, and then flow through the electrical conductor to the ternary lithium positive electrode. Keep the charge in balance.

It can be seen that the basic principle of the lithium titanate battery is that during the charging and discharging process, the corresponding lithium ions are inserted and removed between the positive and negative electrodes to complete the charging and discharging of the battery and the supply of power to the load. The charging and discharging diagram of the lithium titanate battery is shown in the figure.

When the battery is charged, the positive electrode loses electrons, the lithium ions are eluted, and it is embedded in the negative electrode; while the negative electrode is intercalated with lithium ions, the electrons become lithium-rich. The process of discharging is just the opposite. Lithium titanate (Li4TI5O12) is an ideal embedded electrode material during Li+ intercalation or deintercalation. Li+ insertion and deintercalation have little effect on the material structure and are therefore called “zero strain” materials. It guarantees good cycle performance.

Lithium titanate has two different phases of molecular structure - Li7TI5O12 and Li4TI5O12. The crystal structure of Li7TI5O12 and the crystal structure of Li4Ti5O12 are both spinel structures, and the lattice constant changes little, and the volume change is also small. It can avoid the structure of the electrode material in the charge and discharge cycle, which leads to the destruction of the structure, thereby improving the cycle performance and service life of the electrode, reducing the capacity attenuation caused by the increase of the number of cycles, and making the lithium titanate have excellent cycle performance. .

Structure of lithium titanate battery

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 the negative electrode.

Electrolyte: A lithium battery electrolyte using carbon as a negative electrode.

Battery case: A lithium battery case with carbon as the negative electrode.

Lithium titanate battery advantages

Lithium titanate battery has small volume, 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 working temperature range, safe and stable green environment And so on, so it has a very wide application prospect in the field of communication power.

When the lithium titanate is used as the negative electrode material, the potential platform is as high as 1.55V, which is more than 1V higher than the conventional graphite negative electrode material. Although some energy density is lost, it means that the battery is safer. Lu Lu, a technical expert, once said that the battery needs to be low when the battery is rapidly charged. However, if it is too low, the lithium battery will easily precipitate very active metal lithium. This lithium ion is not only conductive but also reacts with the electrolyte. Releases heat, produces flammable gases, and causes a fire. Lithium titanate avoids the precipitation of lithium ions because the high voltage of 1V avoids the negative voltage of 0, thus ensuring the safety of the battery.

Since the lithium titanate battery can be safely used in high temperature and low temperature environments, it also shows its important advantages of wide temperature resistance (especially low temperature resistance). At present, the safe working temperature range of the Yinlong lithium titanate battery is between -50 degrees and 65 degrees, while the ordinary graphite-based negative electrode battery begins to attenuate when the temperature is lower than -20 degrees, and the charging capacity is only -30 degrees. 14% of the total charge capacity does not work properly in cold weather. In addition, since the lithium titanate battery has a volume change of only 1% even if it is overcharged, it is called a zero strain material, which makes it have an extremely long life. Yincang Wei, chairman of Yinlong, once said that the life of Yinlong lithium titanate battery can reach 30 years, which is equivalent to the service life of the automobile, while the average life of ordinary graphite anode material battery is only 3-4 years. Lithium titanate batteries are less expensive from a life cycle perspective.

The last advantage of lithium titanate is its fast charge and discharge capability and high charge rate. At present, the charging rate of Yinlong lithium titanate battery is 10C or even 20C, while the battery charging magnification of ordinary graphite anode material 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

However, the excellent safety performance makes the research on lithium titanate battery become a hot spot, but the lower electronic conductivity (10-13S/cm) and lithium ion diffusion coefficient of Li4Ti5O12 material itself (10-10~10-13cm2/ S) greatly limits the application of large magnification charging and discharging. Some scholars have shown that the nanometer particle size of Li4Ti5O12 can expand the effective reaction area and reduce the diffusion distance, thus significantly improving the rate performance of the material. However, it should be pointed out that the process of nano-materialization of materials is often difficult and requires high cost, and it is difficult to achieve large-scale industrial production at present.

Lithium titanate battery will produce gas continuously in the cycle, which will lead to battery bulge, especially at high temperature, which will affect the contact between positive and negative poles, increase the battery impedance, and affect the performance of the battery. This is one of the main obstacles to the wide application of lithium titanate as a cathode material in batteries.

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