a b s t r a c t
Homogeneous Li4Ti5O12/graphene composite is prepared via an in-situ solid state reaction, after carbon pre-coating has been carried out. Its microstructure is compared with the materials prepared by a similar way, but without carbon coating. The results reveal that the carbon coating not only effectively confines aggregation and agglomeration of the Li4Ti5O12 particles, but also enhances the combination between Li4Ti5O12 particles and graphene sheets. The Li4Ti5O12/graphene composite presents excellent rate capability and low-temperature performance. Even at 120 C, it still delivers a quite high capacity of about 136 mAh g−1. When the charge–discharge tests are performed at −10 ◦C and −20 ◦C, its specific capacities are as high as 149 and 102 mAh g−1, respectively. In addition, the full-cells using LiNi1/3Co1/3Mn1/3O2 as cathode material exhibit good rate capability.
2.3. Electrochemical measurements
The electrochemical performance of the products was evaluated in coin-type cells. In order to make an electrode laminate, a uniform slurry containing 84 wt.% active material, 8 wt.% acetylene black and 8 wt.% polyvinylidene fluoride (PVDF) dispersed in N-methyl-2-pyrrolidinone (NMP) was cast onto an copper current collector. After vacuum drying at 70 ◦C, the laminate was punched into discs (˚ 14 mm) for assembling the cells. The mass loading in the electrode was controlled at about 5 mg cm−2. In the half-cells, various LTO materials were used as working electrode and high-purity lithium metal as counter electrode. In the full-cells, the LiNi1/3Co1/3Mn1/3O2 positive electrode prepared in a similar way (just the current collector was replaced with aluminium foil) and the C-LTO/graphene negative electrode had the same mass loading, and the cell capacity was calculated on the mass of LiNi1/3Co1/3Mn1/3O2. The electrolyte was a solution of 1 M LiPF6 in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1, w/w). The separator is Celgard 2400 microporous polypropylene membrane. The cell performance of samples was evaluated on a multi-channel battery cycler (Neware BTS2300). Galvanostatic charge–discharge tests were performed under different current rates, where 1 C is corresponding to the current density of 150 mAg−1. For the half-cells and the full-cells, the cutoff voltages were set as 2.5–1.0V and 3.0–1.0V, respectively.
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