Lianyi Shao

Comparison of LiVPO4F to Li4Ti5O12 as anode materials for lithium-ion batteries.

In this paper, we reported on a comparison of LiVPO4F to Li4Ti5O12 as anode materials for lithium-ion batteries. Combined with powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, galvanostatic discharge/charge tests and in situ X-ray diffraction technologies, we explore and compare the insertion/extraction mechanisms of LiVPO4F based on the V3+/V2+/V+ redox couples and Li4Ti5O12 based on the Ti4+/Ti3+ redox couple cycled in 1.0-3.0 V and 0.0-3.0 V. The electrochemical results indicate that both LiVPO4F and Li4Ti5O12 are solid electrolyte interphase free materials in 1.0-3.0 V. The insertion/extraction mechanisms of LiVPO4F and Li4Ti5O12 are similar with each other in 1.0-3.0 V as proved by in situ X-ray diffraction. It also demonstrates that both samples possess stable structure in 0.0-3.0 V. Additionally, the electrochemical performance tests of LiVPO4F and Li4Ti5O12 indicate that both samples cycled in 0.0-3.0 V exhibit much higher capacities than those cycled in 1.0-3.0 V but display worse cycle performance. The rate performance of Li4Ti5O12 far exceeds that of LiVPO4F in the same electrochemical potential window. In particular, the capacity retention of Li4Ti5O12 cycled in 1.0-3.0 V is as high as 98.2% after 20 cycles. By contrast, Li4Ti5O12 is expected to be a candidate anode material considering its high working potential, structural zero-strain property, and excellent cycle stability and rate performance.

High performance Na-doped lithium zinc titanate as anode material for Li-ion batteries

A series of Li2−xNaxZnTi3O8 (x = 0, 0.05, 0.10, 0.15, 0.20) are prepared for the first time by a simple solid state method. Upon Na-doping, Rietveld refinement reveals that Na+ takes the 8c tetrahedral sites shared with Li+ and Zn2+ in the structure. Due to the larger ionic radius of Na+ than that of Li+, an increased disorder degree of ion locations in the structure is induced by Na doping. Furthermore, the lithium ion diffusion tunnel is also expanded after Na doping. Thus, higher lithium ion diffusion coefficient can be observed for all the Na-doped Li2ZnTi3O8 samples. However, phase analysis shows that high Na-doping content can result in the formation of impurity in the as-obtained titanates. Besides, the existence of too many Na ions in the spinel also decreases the structural stability. Therefore, Na-doping with low dose is beneficial to improve the electrochemical performance of Li2ZnTi3O8. Electrochemical evaluations show that Li1.95Na0.05ZnTi3O8 has the best lithium storage property among all the Li2−xNaxZnTi3O8. It can be found that Li1.95Na0.05ZnTi3O8 can deliver a reversible capacity of 267.3 mA h g−1 after 50 cycles. This finding can provide an experimental support to synthesize high performance Ti-based materials by Na doping.

Ex situ FTIR spectroscopy study of LiVPO4F as cathode material for lithium-ion batteries

The LiVPO4F as cathode material for lithium-ion batteries was synthesized through two steps of solid-state reactions and investigated by ex situ Fourier transform infrared (FTIR) spectroscopy for the initial charge and discharge cycle. The characterization of the effect on the structure of the LiVPO4F in the process of lithium-ion insertion/extraction at a molecular level by ex situ FTIR spectroscopy is helpful for the mechanism research for lithium-ion insertion/extraction and the improvement of the performance of lithium-ion batteries. In the process of the initial cycle, new bands of VPO4F appear in the charge and the featured bands of LiVPO4F reappear in the discharge. In this paper, ex situ FTIR spectra indicates that the structure of the LiVPO4F in the process of lithium-ion insertion/extraction is almost not affected, which clearly states that the LiVPO4F possesses stable structure as cathode material. Consequently, the LiVPO4F might be expected as a potential cathode replacement for commercial lithium-ion batteries.

Enhanced lithium storage property of Na-doped Li2Na2Ti6O14 anode materials for secondary lithium-ion batteries

In this paper, a series of Na-doped Li2Na2Ti6O14 samples are synthesized by a simple solid-state reaction method through Li-site substitution with Na. Morphology observation shows that all five materials are well crystallized with a particle size in the range of 150–300 nm. Electrochemical analysis shows that Li1.95Na2.05Ti6O14 exhibits lower charge–discharge polarization (0.05 V) than that (0.11 V) of other Li2−xNa2+xTi6O14 samples (x = 0.00, 0.10, 0.15, 0.20). As a result, Li1.95Na2.05Ti6O14 has the highest initial charge capacity of 243.6 mA h g−1, and maintains a reversible capacity of 210.7 mA h g−1 after 79 cycles. For comparison, Li2−xNa2+xTi6O14 (x = 0.00, 0.10, 0.15 and 0.20) samples only hold a reversible capacity of 159.1, 203.5, 190.1 and 156.7 mA h g−1, respectively. Moreover, Li1.95Na2.05Ti6O14 also delivers the best rate performance compared with the other four samples, with a charge capacity of 221.1 mA h g−1 at 200 mA g−1, 211.9 mA h g−1 at 300 mA g−1, and 198.7 mA h g−1 at 400 mA g−1. Besides, the reversible in situ structural evolution proves that Li1.95Na2.05Ti6O14 is a stable host for lithium storage. All the improved electrochemical properties of Na-doped Li2Na2Ti6O14 should be attributed to the Na-doping with low content, which reduces the charge–discharge polarization and improves the ionic conductivity.