Recently, Toshiba Corporation of Japan released a news on its official website that the company’s Toshiba Infrastructure Systems and Solutions company TISS entered into an agreement with Sojitz and Brazilian mining company CBMM to jointly develop TiNb2O7, the next generation lithium ion battery anode material. According to reports, the material has a high volume energy density, fast charge and discharge, and long-life characteristics that can meet the application requirements of electric vehicles. What? Toshiba has also begun to get involved in the power battery? Yes, right, In fact, Toshiba had been in 2008 as early as Started development of lithium titanate batteries with safety, long life, and fast charge characteristics. However, lithium titanate batteries have a fatal shortcoming—energy density is too low. Toshiba Corporation introduced a new generation of power battery products, SCiBTM, in 2017. This product uses neodymium-titanium oxide NTO as a negative electrode, NTO compound volumetric capacity is twice that of graphite negative electrode, significantly improve the performance of SCiBTM battery, the company plans to bring the product to market in 2020.
Currently, there are two major types of negative electrode materials on the market. One is graphite negative electrode material, which occupies the vast majority of the market, and one is silicon-carbon material. It has achieved more applications in high specific energy battery market. So what is this ghost of Toshiba's NTO? In fact, we can see some clues from Toshiba's press release. This NTO material has a deep relationship with LTO materials. Toshiba has been deeply plowing in the field of lithium titanate (LTO) batteries for many years. Although there was no substantial breakthrough in LTO battery, but accumulated experience in the modification and development of LTO materials, this lanthanum titanium oxide NTO material is developed on the basis of LTO materials. Xiaobian also specially Toshiba’s article on the material published in the top journal JPS was found, providing a comprehensive understanding of Toshiba’s development of NTO materials.
The NTO material developed by Toshiba is mainly composed of spherical secondary particles. The surface of the particles has been coated with carbon. The reversible capacity of this material is 341mAh/g, which is close to that of graphite materials. NCM622 is used as the positive electrode and NTO is used as the material. 49Ah battery made from a negative electrode, with a volumetric energy density of 350Wh/L, a maximum input power of 10kW/L (50%SoC), a minimum of 6 minutes from 0% SoC charging to 90% SoC, and 7,000 cycles at 1C magnification The capacity retention rate is up to 86%, and the life expectancy is over 14,000 times. It almost perfectly meets the demand for power batteries for electric vehicles.
The formula of TNO slurry was 91wt% TNO, 5% graphite conductive agent and 2% CMC, 2% SBR. Tests showed that the density of high-density TNO materials developed by Toshiba Corporation can reach 2.7g/cm3. It is much higher than the compacted density of graphite materials. From the results of cyclic voltammetry, the potentials of LiN and LiLi of TNO are close to 1.56V and 1.69V, respectively.
The following figure shows the results of the AC impedance test of the TNO material under different Li-loading levels. The equivalent circuit in the figure is used for the fitting. Ro is the ohmic impedance, Rp is the polarization impedance, and it contains the charge exchange impedance and the surface film impedance. Zw is Diffusion impedance, from the test results, the ohmic resistance Ro does not change substantially under different Li-inserted conditions, but Rp changes significantly with the number of Li-doped NTO materials. When the amount of lithium intercalated x is between 0-0.6. In the interim, Rp decreases with the increase in the amount of intercalated lithium. At x=0.6-1.6, Rp remains almost constant. At x=1.6-3.2, Rp increases significantly with the increase of x, while the polarization of the battery The increase is not significant. In the range of x>3.2, Rp slightly rises when the amount of intercalation lithium increases, but the polarization of the material increases significantly, indicating that the diffusion resistance of Li+ is the main limit compared to the charge exchange impedance at this time. factor.
The black curve below shows the test results of the high-density carbon-coated TNO material developed by Toshiba Corporation. The blue curve is the low-density TNO material (70% NTO, 20% acetylene black, 7% CMC and 3% SBR). For the high-density TNO material without carbon coating, it can be seen from the figure that the low-density TNO exhibits a very good rate performance due to the addition of a large amount of conductive agent, but due to the lower content of the active material, the volumetric specific capacity It is obviously lower than the carbon-coated high-density TNO material. This test shows that the TNO material greatly improves the rate performance of the material after 2% carbon coating, while maintaining the advantage of high volume energy density.
To verify whether this material can be used in electric vehicles, Toshiba used carbon-coated high-density TNO materials and NCM622 materials to produce a 49-Ah power battery. The battery voltage platform was 2.25V, and the volume energy density was 350Wh/L. The weight energy density reaches 138Wh/kg. The test shows that the battery has a capacity retention rate of 93% at 10C discharge rate. This can not only meet the demand of pure electric vehicles, but also fully meet the demand of plug-in hybrid vehicles. The battery also showed excellent low temperature performance. The discharge capacity of the battery can still reach 63% at room temperature at -30°C.
Fast charge performance is also a very important point of our concern. Tests have shown that the time required for the battery to fully charge 90% at 4C, 6C, 8C and 10C rates is 13.6, 9.0, 6.9 and 5.5 minutes respectively. It takes less than 6 minutes to fully charge 90% of its capacity at a charging rate. About one song time, this fast charging speed has made electric vehicles comparable in convenience to fuel vehicles. Low temperature charging at -10°C In the test, it takes only 12 minutes to fill the capacity of 90% at 5C rate, and the negative electrode has no lithium precipitation at all, which greatly improves the convenience of the use of electric vehicles in the winter.
In addition to the above performance indicators, the power battery is the most concerned about the cycle life of the power battery. The following figure shows the cycle performance of the TNO/NCM battery at 1C rate. From the test results, the battery capacity is maintained after 7000 cycles. The rate is still 86%, and the 80% capacity retention life is expected to reach around 14,000 cycles, while the NCM/graphite battery with a graphite negative electrode has a capacity retention rate of 80% after 3400 cycles, indicating that TNO/NCM has a service life. This is a very big advantage, which is of great significance in reducing the life cycle cost of electric vehicles.
In general, this TNO negative electrode material developed by Toshiba Corp. is close to the graphite material in terms of specific capacity, but because its compaction density is much higher than that of graphite material, it compensates for the higher disadvantages of the voltage platform, from the TNO material and the NMC 622 material. The prepared power battery is close to the LFP battery in terms of volumetric energy density and weight energy density, and the TNO material exhibits excellent fast charge performance, and can be filled with 90% capacity within 6 minutes at room temperature, which greatly improves the use of the electric vehicle. Convenience, and TNO material also showed excellent performance in cycle life, cycling 7000 times at 1C rate, capacity retention rate up to 86%, greatly reducing the life cycle cost of electric vehicles, now The only thing to worry about is the cost of this material. If it can approach the graphite material, then the material will have a huge market prospect.
