Study on lithium titanate hydrate technology for fast charge and discharge and stable circulating lithium ion battery

【introduction】

At present, the commonly used lithium ion batteries use organic electrolytes, and the electrolyte LiPF6 is a substance which is easily decomposed by water. Therefore, in the conventional concept, the electrode materials of lithium ion batteries are required to be calcined at a high temperature to sufficiently remove water. However, this causes unavoidable side reactions such as particle agglomeration and grain coarsening.

[Introduction]

On September 20th, Nature Communications published a book entitled "A Lithium Titanate Hydrate - Lithium Titanate Hydrates with Superfast and Stable Cycling" (Lithium Titanate Hydrates with Superfast and Stable Cycling) Research paper in Lithium Ion Batteries). This achievement is aimed at the field of titanium-based energy storage materials, and reported a series of lithium titanate hydrates, which are applied to lithium ion batteries with long cycle life and high rate performance, which effectively expands the research scope of energy storage materials and provides electrode materials. New ideas for modification. The author of the paper is Professor Tang Zilong from Tsinghua University School of Materials, Lu Jun, a researcher at the Argonne National Laboratory, and Professor Li Ju from the Massachusetts Institute of Technology. The first author is Wang Shitong, a 2012 Ph.D. student at the School of Materials, Tsinghua University.

[This article highlights]

The Li-H-Ti-O system materials discovered by the research team are related to the Li-Ti-O system and Ti-O system materials (including materials after nanocrystallization, doping and coating) which are excellent at home and abroad. It has comparable or even superior electrochemical properties. As an electrode material containing "water", such lithium titanate hydrate can achieve a stable cycle of up to tens of thousands of times in a high-voltage organic electrolyte system, which breaks the traditional perception. The so-called "crystal water" firmly bonded inside the material crystal not only does not destroy the electrochemical performance of the electrode material under the organic electrolyte system, but promotes the diversity of the crystal structure (such as two-dimensional layer) and the construction of the nanocomposite. Essentially increases the ion diffusion coefficient of the material.

[Graphic introduction]

Fig.1 Synthetic route diagram of Li2O-TiO2-H2O ternary phase diagram and lithium titanate hydrate

Fig. 2 Schematic diagram of the synthesis process of lithium titanate hydrate and the process of rapid lithium insertion/delithiation

Figure 3 Lithium titanate hydrate precursor during heating and dehydration

(a) Thermogravimetric analysis, (b) Off-site XRD analysis and (c) In-situ synchrotron radiation HEXRD contour map (where red indicates the highest diffraction intensity and blue indicates the lowest diffraction intensity); HN, LS and DN electrode materials (d) Stable charge-discharge curves in the voltage range 1.0~2.5 V, current density 100 mA g-1, (e) rate performance and (f) cycle performance comparison at 4000 mA g-1.

Figure 4 Electrochemical mechanism analysis of lithium titanate hydrate

(a) anodic peak current (jp) response of LS, HN and DN for scan rate (v); (b) in situ synchrotron radiation for LS electrode material at 100 mA g-1 for the third cycle XRD results (c) Comparison of lithium ion diffusion coefficients of LS, HN and DN electrodes at different SOCs; (d) HRTEM image of HN nanomaterials, enlarged view of the box in (e)d and (f) selected area electron diffraction Figure.

Figure 5 Electrochemical performance of AC//HN lithium ion capacitor

(a) CV scan curves from 10 mV s-1 to 100 mV s-1, (b) Ragone plots of energy density and power density, and (c) cycle stability at current densities of 2000 mA g-1 With the Coulomb efficiency map.

[Outlook]

Using the new modification of Li-H-Ti-O system materials and its essential and universal characteristics, the degree of freedom of electrode material performance adjustment and optimization can be extended, and other hydrogen-containing components are expected. The application of transition metal compound systems in the field of energy materials provides greater inspiration and guidance.