Single-phase lithium manganese borate, LiMnBO3, was obtained at the temperature higher than 850°C by one-step solid state reaction without using carbon black in the starting materials. The initial specific discharge capacity for the cathode active material was 75.5mAh/g at the current density of 5mA/g and the mean fade of capacity was 0.09% per cycle except for the first cycle. The LiMnBO3 compound maintained a specific discharge capacity of 42.3mAh/g even at the current density of 50mA/g and the capacity fade per cycle was only 0.2% during 40 cycles. The cyclic voltammograms (CV) curves show that the Mn3+/Mn2+ redox couple situated at 2.23 and 4.13V can be clearly observed during anodic and cathodic sweeps. Combined the cyclic voltammograms results with the X-ray diffraction patterns of electrodes before and after cycling, where no significant change of the peak currents and the peak potentials during cycling, it was anticipated that the extraction and insertion of Li-ions are totally reversible in this compounds and the hexagonal structure for LiMnBO3 can be maintained after long cycles under high charge and discharge rate.

Li-ion battery cathode materials Li3V2-xCrx(PO4)3/C(x=0,0.05,0.10 and 0.20)were synthesized by sol-gel method.The effects of Cr doping on the samples were studied by the methods of XRD,SEM,charge-discharge,cyclic voltammetry and conductivity test.The samples were single phase.Although the initial specific capacity at low rate(0.2 C)decreased with the increasing of x,but proper Cr doping could improve its cycle and rate performance.When charge-discharge at 0.2 C and 4.0 C,the initial specific discharge capacities of Li3V1.90Cr0.10(PO4)3/C were 171.4 mAh/g and 130.2 mAh/g,respectively,the capacity retention at the 100th cycle were 78.6% and 88.9%,respectively.

Cr-doped Li3V2−xCrx(PO4)3/C (x=0, 0.05, 0.1, 0.2, 0.5, 1) compounds have been prepared using sol–gel method. The Rietveld refinement results indicate that single-phase Li3V2−xCrx(PO4)3/C with monoclinic structure can be obtained. Although the initial specific capacity decreased with Cr content at a lower current rate, both cycle performance and rate capability have excited improvement with moderate Cr-doping content in Li3V2−xCrx(PO4)3/C. Li3V1.9Cr0.1(PO4)3/C compound presents an initial capacity of 171.4mAhg−1 and 78.6% capacity retention after 100 cycles at 0.2C rate. At 4C rate, the Li3V1.9Cr0.1(PO4)3/C can give an initial capacity of 130.2mAhg−1 and 10.8% capacity loss after 100 cycles where the Li3V2(PO4)3/C presents the initial capacity of 127.4mAhg−1 and capacity loss of 14.9%. Enhanced rate and cyclic capability may be attributed to the optimizing particle size, carbon coating quality, and structural stability during the proper amount of Cr-doping (x=0.1) in V sites.

Lithium iron phosphate (LiFePO4) cathode material has been synthesized by a solid-state reaction. The XRD patterns of the samples show that the single-phase LiFePO4 compounds can be obtained in our experimental conditions. According to Popa theory, using the result from Rietveld refinement, the shape and the size of crystallite can be obtained. The result shows that the use of carbon gel in precursors do not change the structure of the crystal, but it can inhibit the particle growth and restrain the anisotropy growth of the grain at a lower temperature. At a higher temperature, carbon-coated LiFePO4 shows an anisotropy growth, i.e. growth rate along (100) crystal plane is more rapid than that of (111) crystal plane. In our experimental conditions, a spherical carbon-coated LiFePO4 can be synthesized successfully at 650°C. The electrochemical testing indicated that the spherical carbon-coated LiFePO4 had the excellent performance. Its initial specific capacities were 156.7mAhg−1 under the rate of C/10. At the 50th cycle, the reversible specific capacities were found to approach 151.2mAhg−1 (the ratio of 96.5% of initial capacity).

LiFePO4 samples have been synthesized by mixing stoichiometric amounts of (NH4)2HPO4, FeC2O4·2H2O, and LiF. During synthesis, carbon gel was used as the carbon source. Single-phase LiFePO4 can be formed when the heating temperature ranges from 650 to 800 °C and it is decomposed into Li4P2O7, Li3PO4, Fe2P, and Li3P7 when the temperature comes to 850 °C. We find that the ratio of the lattice parameter (a/c) decreases with the increasing temperature, thereby increasing the Li+ diffusion channel length. Both the decrease of a/c and the abrupt crystal growth are expected to contribute to the monotonic decrease of the initial capacity of the samples. The sample heated at 650 °C with a smaller uniform particle size and relative higher specific surface area (8.2 m2/g) shows an excellent electrochemical performance. The initial specific capacity of 156.7(3) mAh/g is obtained at the rate of C/10.