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Carbon-coated Li 2 MnSiO 4 nanocrystallites are synthesized via a solid state reaction, and their cathode and anode performance is comparatively studied. The Li 2 MnSiO 4 cathode shows an initial charge/discharge capacity of 405/134 mAh g −1 at a current density of 16.6 mA g −1 , and a low charge/discharge capacity of 93/66 mAh g −1 during the 20th cycle. Partial Li 2 MnSiO 4 cathode decomposes at 4.56 V ( vs Li + /Li) during the initial charge. Interestingly, the Li 2 MnSiO 4 anode exhibits a high initial discharge/charge capacity of 658/388 mAh g −1 at a current density of 20 mA g −1 , and a discharge/charge capacity of 459/456 mAh g −1 during the 50th cycle. Li 2 MnSiO 4 anodes also have stable and good rate capabilities. The Li 2 MnSiO 4 crystallites as anode decompose during cycling, and their capacity increases simultaneously. It is proposed that Li 2 MnSiO 4 anode converts energy via a reversible conversion reaction. [ABSTRACT FROM AUTHOR]

The LiMnFePO/C nanocrystallites with a uniform size (∼50 nm) are successfully prepared by employing a facile solvothermal method at 180 °C. Amphiphilic carbonaceous material (ACM) is chosen as the carbon precursor and forms a homogeneous carbon layer covering the LiMnFePO particles. The as-prepared LiMnFePO/C sample, with a high Brunauer-Emmett-Teller (BET) surface area of 69.3 m g, is used as the cathode material for lithium-ion batteries (LIBs) and delivers a reversible capacity of 158 mAh g at 0.05 C. It shows remarkable rate capability with discharge capacities of 130 mAh g at 1 C, 105 mAh g at 10 C and 99 mAh g at 30 C. Meanwhile, the material maintains 121 mAh g at 1 C after 150 cycles with 93 % capacity retention. The kinetic behaviors of LiMnFePO/C sample are investigated by high throughout cyclic voltammetry. The small particle size, partial Fe substitution, and homogeneous carbon coating make a synergetic effect on enhancing the sample's electrochemical properties. [ABSTRACT FROM AUTHOR]

Lithium-rich layered oxide Li[LiNiMn]O, which also can be written as 0.6LiMnO·0.4LiNiMnO or 0.9Li[LiMn]O·0.4LiNiMnO, is synthesized using a solid-state reaction method. Its crystal structure and electrochemical behavior as the cathode material in lithium-ion batteries are studied. A reaction mechanism is proposed to interpret its unique electrochemical behavior shown in the first charge-discharge cycle. It includes four reactions: (1) LiNiMnO → Li + NiMnO + e, (2) Li[LiMn]O → Li + [LiMn]O + e, (3) [LiMn]O → 1/3 Li + 2/3 MnO + 2/3 O· + e, and (4) Li + NiMnO + e → LiNiMnO. The extraction of oxygen atoms (O·) in the reaction (3) results in the crystal structure rearrangement. Based on this hypothesis, it is found that the expected capacity of activated lithium-rich layered oxide xLiMnO·(1 − x)LiNiMnO (0 ≤ x ≤ 1) increases from 230 to 280 mAh g with increasing x value. Li[LiNiMn]O has an expected total first charge capacity of 396 mAh g, but its expected capacity is only 247 mAh g due to an initial capacity loss caused by the oxygen loss. Experimentally, within a charge-discharge voltage window from 2.0 to 4.8 V, Li[LiNiMn]O delivers a charge capacity of 310 mAh g and a discharge capacity of 215 mAh g, respectively, at 40 mA g during the first cycle. The electrochemical kinetic behavior of Li[LiNiMn]O is controlled by the charge-transfer process rather than by Li diffusion or blockage of solid-electrolyte interphase (SEI) layers at the end of Li extraction in the first charge. [ABSTRACT FROM AUTHOR]

To enhance the rate and cyclic performances of LiMnPO 4 cathode material for lithium-ion batteries, Mn is partially substituted with Fe, and LiMn 1− x Fe x PO 4 ( x = 0.2, 0.3, 0.4, 0.5) solid solutions are synthesized and investigated. Amphiphilic carbonaceous material (ACM) forms well carbon coating and connects the LiMn 1− x Fe x PO 4 crystallites by a three-dimensional (3D) carbon network. The synergetic Fe substitution and carbon connection obviously improve the samples’ rate capacities and cyclic stability. The optimized LiMn 0.6 Fe 0.4 PO 4 /C sample delivers discharge capacities of 160 mA h g −1 at 0.05 C, 148 mA h g −1 at 1 C, and 115 mA h g −1 at 20 C. All samples have well capacity retention (>92%) after 50 charge/discharge cycles at 1 C. The enhanced electrochemical properties are mainly attributed to the improvement of Li ion and electron transport in the LiMn 1− x Fe x PO 4 /C samples, respectively mainly resulting from their modified crystal structures caused by Fe substitution and the 3D carbon coating/connection originating from ACM carbonization. LiMn 1− x Fe x PO 4 materials exhibit two discharge plateaus at ∼4.0 and ∼3.5 V (vs. Li + /Li), whose heights respectively reflect the redox potentials of Mn 3+ /Mn 2+ and Fe 3+ /Fe 2+ couples. The plateaus’ lengths correspond to the Mn/Fe ratio in LiMn 1− x Fe x PO 4 and are affected by the kinetic behavior of samples. Though the ∼4.0 V plateau shrinks with increasing discharge rate, the ∼3.5 V plateau may slightly elongate. Moreover, the Fe substituted in the partial Mn sites could significantly improve the Li ion diffusion, thus enhance the kinetic behaviors of LiMn 1− x Fe x PO 4 . [ABSTRACT FROM AUTHOR]

Abstract: The high discharge potential of LiMnPO4, 4.1 V vs. Li/Li+, and its theoretical capacity of 170 mAh g−1 make it a promising candidate as a cathode material in lithium-ion batteries. But extremely low electronics conductivity, slow lithium diffusion kinetics, and the Jahn-Teller effect of Mn3+ limit the electrochemical performances of LiMnPO4. In this work, the pre-synthesized and defined FePO4·2H2O nanocrystallites are used as one of the raw materials to synthesize LiFe1−x Mn x PO4/C (x = 0.85, 0.75, 0.65) composites via solid-state reactions. The synthesized LiFe1−x Mn x PO4 samples show well-crystallized structures and have enhanced electrochemical properties. There exist two plateaus around 3.5 and 4.1 V on both of their charge and discharge curves. Among the samples, the Fe0.25Mn0.75PO4 one exhibits the longest high-voltage charge/discharge plateau at 4.10 V/4.05 V, and has an average discharge voltage of ∼3.78 V vs. Li/Li+ and a discharge capacity of ∼130 mAh g−1 at 0.05 C rate. For the Fe0.25Mn0.75PO4 sample, the noticeable improvement of its electrochemical performances is mainly attributed to iron substitution, the appropriate Mn/Fe ratio, and the well-ordered crystal structure forming by using FePO4·2H2O nanocrystallites as one of the raw materials. [Copyright &y& Elsevier]