Large cations such as potassium ion (K+) and sodium ion (Na+) could be introduced into the lithium-ion (Li-ion) battery system during material synthesis or battery assembly. However, the effect of these cations on charge storage or electrochemical performance has not been fully understood. In this study, sodium ion was taken as an example and introduced into the lithium titanium oxide (LTO) anode through the carboxymethyl cellulose (CMC) binder. After the charge/discharge cycles, these ions doped into the LTO lattice and improved both the lithium-ion diffusivity and the electronic conductivity of the anode. The sodium ion’s high concentration (>12.9%), however, resulted in internal doping of Na+into the LTO lattice, which retarded the transfer of lithium ions due to repulsion and physical blocking. The systematic study presented here shows that large cations with an appropriate concentration in the electrode would be beneficial to the electrochemical performance of the Li-ion battery.Keywords:lithium-ion battery;LTO anode;sodium doping;lithium-ion diffusivity
The capacity of Li4Ti5O12 (LTO) at high rates is limited due to the polarization caused by its modest Li-ion (Li+) diffusion coefficient and low electrical conductivity. Coating with ionic conductors is an available method to ameliorate charge transport. Li1+xAlxTi2–x(PO4)3 ion conductors with thermal, chemical, and electrochemical stabilities have been proven to be modification materials for electrodes. Herein, the Li1.4Al0.4Ti1.6(PO4)3 (LATP) precursor dispersion with optimized preparation is applied to the surface modification of LTO by a dynamic mix-drying method. A proper amount of LATP ultrafine particle coating could develop the ion transport rate in the electrode and restrain side reactions. The 2 wt % LATP–LTO anode exhibits an optimized capacity of 168.2 mA h g–1 at 0.1 A g–1 and retains 96.7% of its capacity after 5000 cycles at 5.0 A g–1, while the P-LTO anode retains 86.3% of the capacity. Improved Li+ transport and interface stability in the electrodes lead to the boosted rate and cycling stability. The LATP-modified LTO composites provide a possibility for the further application of related materials in the energy storage field.
Enhancing the electron/ion transfer ability of Li 4 Ti 5 O 12 materials is very important to achieve advanced high-rate and long-life anode in lithium ion batteries (LIBs). Here, for the first time, we report Li 4 Ti 5 O 12 /nitrogen, sulfur co-doped porous graphene composites (LTO/N, S-PG) via one-step facile calcination and activation process by using LiOH as Li source and activating agent. Mechanisms underlying the beneficial effects of N, S co-doped graphene for LTO anode were substantiated by the Density Functional Theory (DFT) calculations, revealing that co-doped N and S atoms not only significantly facilitate Li + adsorption, but also ameliorate Li + diffusion in graphene. Furthermore, the synergistic effects of nanosized LTO and porous graphene endow the composites with efficient Li + diffusion channels and electron-conductive networks. Therefore, the LTO/N, S-PG can deliver extraordinarily high rate capability ( e.g. 130 mA h g −1 at 80 C and 123 mA h g −1 at 100 C), and excellent cycling stability (83.1% capacity retention after 4000 cycles at 20 C). In addition, their superior electrochemical performance was also demonstrated in the full cells with LiNi 0.5 Mn 1.5 O 4 cathode, which displayed 89.5% capacity retention after 500 cycles at 5 C. These results suggest the great promise of using the LTO/N, S-PG as a novel anode material for high-rate and long-life LIBs.
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