A new P2-structured oxide Na0.8Ni0.4Mn0.6O2 was synthesized using a solid reaction method in which Na2CO3, MnO2 and NiO were used as starting materials. This oxide has a high amount of electrochemically active Ni and exhibits good electrochemical intercalation behavior of Na ions, including good rate capability and good cycle performance at both room temperature and elevated temperature. It displays two apparent voltage plateaus at about 3.6 and 3.3 V, and its discharge capacity reaches 92 mAh·g−1 at 0.1C in the voltage range of 2.0–4.0 V. At 1.0C, its discharge capacity reaches 85.3 mAh·g−1. After 80 cycles at different current rates, the as-prepared sample exhibits good capacity retention. At elevated temperature of 55 °C, the discharge capacity remains the same at low current rate of 0.1C, but at high current rate of 1.0C, the discharge capacity is a little lower than that at room temperature.

•The laws of calcination temperature affecting oxygen deficiency in LiNi0.5Mn1.5O4 were investigated.•A model of oxygen deficiency in spinel LiNi0.5Mn1.5O4 is set up.•The coulomb efficiency of LiNi0.45Cr0.1Mn1.45O4 in the first charge and discharge cycle reached a high value of 89.1%.The oxygen deficiency is an important factor to affect the electrochemical properties of spinel LiNi0.5Mn1.5O4. In this study, we investigated how oxygen deficiency in spinel LiNi0.5Mn1.5O4 was affected by calcination temperature and oxygen partial pressure. The oxygen deficiency as a function of calcination temperatures has been modeled. Doping elements have influence on oxygen deficiency. The oxygen dissipation of Cr-doped compounds LiNi0.45Cr0.1Mn1.45O4 at high temperature is less than pristine LiNi0.5Mn1.5O4. Under the same calcination and cooling condition, there more oxygen deficiency remained in Fe and Cr-doped compounds than in pristine LiMn1.5Ni0.5O4. The coulomb efficiencies of LiNi0.45Cr0.1Mn1.45O4 in the first charge and discharge cycle reached a high value of 89.1%.

Spinel LiNi0.5Mn1.5O4 is a very important and promising cathode material for lithium ion batteries. The strategy of doping elements is a common used way to improve its electrochemical properties. The action mechanism of doping elements in LiNi0.5Mn1.5O4 is complex. In this study, we synthesized the Cr, Fe-doped compounds LiNi0.45M0.1Mn1.45O4 (M = Cr, Fe) and pristine compound LiNi0.5Mn1.5O4 at the same annealing conditions. The as prepared samples display different morphological features. The thermogravimetric analysis shows different situation for these samples. Oxygen dissipation in the Cr-doped compound at high temperature is less than the other two samples. The XPS spectra display that the doping elements have influences on the chemical valence of Ni, and result in more Ni(III) amount in the Cr, Fe-doped products. The doped compounds exhibit excellent rate capability. At 10C-charge/10C-discharge rate, their capacities are 85 mAh g−1, 74 mAh g−1 and 50 mAh g−1 for LiNi0.45Fe0.1Mn1.45O4, LiNi0.45Cr0.1Mn1.45O4 and LiNi0.5Mn1.5O4, respectively.

The pure phase P2-Na2/3Ni1/3Mn2/3O2 was synthesized by a solid reaction process. The optimum calcination temperature was 850 °C. The as-prepared product delivered a capacity of 158 mAh g−1 in the voltage range of 2–4.5 V, and there was a phase transition from P2 to O2 at about 4.2 V in the charge process. The P2 phase exhibited excellent intercalation behavior of Na ions. The reversible capacity is about 88.5 mAh g−1 at 0.1 C in the voltage range of 2–4 V at room temperature. At an elevated temperature of 55 °C, it could remain as an excellent capacity retention at low current rates. The P2-Na2/3Ni1/3Mn2/3O2 is a potential cathode material for sodium-ion batteries.

In the past, the electrochemical properties of spinel LiNi0.5Mn1.5O4, i.e. rate capability at room temperature and cycle performance at elevated temperature, were not satisfactory. In this study, the influence of glycolic acid on the electrochemical properties of spinel LiNi0.5Mn1.5O4 was studied. With some amount of glycolic acid as an additional reactant, spinel LiNi0.5Mn1.5O4 was synthesized, and its electrochemical properties were improved. In addition, the mechanism of capacity decay at elevated temperature was also studied, which presents constructive view to further improve the electrochemical properties of spinel LiNi0.5Mn1.5O4.

The formation of impurity LixNi1−xO when synthesizing spinel LiNi0.5Mn1.5O4 using solid state reaction method, and its influence on the electrochemical properties of product LiNi0.5Mn1.5O4 were studied. The secondary phase LixNi1−xO emerges at high temperature due to oxygen deficiency for LiNi0.5Mn1.5O4 and partial reduction of Mn4+ to Mn3+ in LiNi0.5Mn1.5O4. Annealing process can diminish oxygen deficiency and inhibit impurity LixNi1−xO. The impurity reduces the specific capacity of product, but it does not have obvious negative effect on cycle performance of product. The capacity of LiNi0.5Mn1.5O4 that contains LixNi1−xO can deliver about 120 mAh g−1.Highlights► This manuscript investigated the influence of impurity LixNi1−xO on the electrochemical properties of LiNi0.5Mn1.5O4. ► The impurity LixNi1−xO is usually present in products synthesized by solid state methods which are used in industry. ► So this study is useful to produce LiNi0.5Mn1.5O4 commercially.

The spinel compound Li4Ti5O12 was synthesized by a solid state method. In this synthesizing process, anatase TiO2 and Li2CO3 were used as reactants. The influences of reaction temperature and calcination time on the properties of products were studied. When calcination temperature was 750 °C and calcination temperature was 24 h, the products exhibited good electrochemical properties. Its discharge capacity reached 160 mAh g−1 and its capacity retention was 97% at the 50th cycle when the current rate was 1 C. When current rate increased to 10 C, its first discharge capacity could reach 136 mAh g−1, and its capacity retention was 85% at the 50th cycle.Highlights► An easy solid state method was used to synthesize Li4Ti5O12. ► The product exhibited excellent electrochemical performances. ► For example, the capacities were 134 and 126 mAh g−1 at 5 and 10 °C, respectively. ► The synthesizing conditions were discussed. ► It provides some useful references for synthesizing Li4Ti5O12.

Spinel compound LiNi0.4Mn1.5Cr0.1O4 (LNMCO) and Li4Ti5O12 (LTO) were synthesized by the sol-gel method and the solid-state method, respectively. The particle sizes of the products LiNi0.4Mn1.5Cr0.1O4 and Li4Ti5O12 were 0.5 to 2 um and 0.5 to 0.8 um, respectively. All samples exhibited excellent electrochemical properties. A LiNi0.4Mn1.5Cr0.1O4/Li4Ti5O12 (LNMCO/LTO) cell was fabricated and was demonstrated to exhibit good electrochemical properties at the high current rate of 1 C. When the specific capacity was determined based on the mass of the LNMCO cathode, the LNMCO/LTO cell delivered 125 mAh g−1 at 1 C and 77 mAh g−1 at 5 C. The capacity retentions after 30 cycles were 94.4 % and 83.1 %, respectively.

The spinel compound LiCr0.1Ni0.4Mn1.5O4 is synthesized by a sol–gel method. In this synthesizing process, Li(CH3COO)·2H2O, Ni(CH3COO)2·4H2O, Mn(CH3COO)2·4H2O and Cr(NO3)3·9H2O are used as reactants, and malic acid as chelating agent. The reaction takes place at 900 °C for 8 h. The electrochemical performances of the as-prepared sample are measured at different current rates. In the range of 3.5–5.0 V, its discharge capacities are 141, 125 and 95 mAh g−1 at 0.5, 1 and 5 C, respectively. Based on cycle voltammetry results, the diffusion coefficient of Li+ is calculated as 6.75 × 10−10 cm2 s−1 at 4.07 V in oxidation process.

The spinel material LiNi0.5Mn1.5O4 displays a remarkable property of high charge/discharge voltage plateau at around 4.7 V. It is a promising cathode material for new-generation lithium-ion batteries with high voltage. Recently, a lot of researches related to this material have been carried out. In this review we present a summary of these researches, including the structure, the mechanism of high voltage, and the latest developments in improving its electrochemical properties like rate ability and cycle performance at elevated temperature, etc. Doping element and synthesizing nanoscale material are effective ways to improve its rate ability. The novel battery systems, like LiNi0.5Mn1.5O4/Li5Ti4O12 with good electrochemical properties, are also in progress.

The electrochemical properties of spinel compound LiNi0.5Mn1.2Ti0.3O4 were investigated in this study. The chemicals LiAc·2H2O, Mn(Ac)2·2H2O, Ni(Ac)2·4H2O, and Ti(OCH3)4 were used to synthesize LiNi0.5Mn1.2Ti0.3O4 by a simple sol-gel method. The discharge capacity of the sample reached 134 mAh/g at a current rate of 0.1C. The first and fifth cycle voltammogram almost overlapped, which showed that the prepared sample LiNi0.5Mn1.2Ti0.3O4 had excellent good cycle performance. There were two oxidation peaks at 4.21 V and 4.86 V, and two reduction peaks at 4.55 V and 3.88 V in the cycle voltammogram, respectively. By electrochemical impedance spectroscopy and its fitted result, the lithium ion diffusion coefficient was measured to be approximately 7.76 × 10−11 cm2/s.