Engineering the electrode/electrolyte interface through the addition of electrolyte additives has proven to be a promising strategy for enhancing the cell performance, and there are distinguishable discrepancies in the effect of 1,3,2-dioxathiolane-2,2-dioxide (DTD) as an electrolyte additive in different cell systems. Herein, DTD is added into the electrolyte for the Li/LiMn0.8Fe0.2PO4 cell and its functions on the LiMn0.8Fe0.2PO4 cathode are studied. The result demonstrates that a beneficial effect on the LiMn0.8Fe0.2PO4 performance is generated by adding DTD into the electrolyte, which is attributed to the decreased products arising from the interfacial side reactions on the surface of the LiMn0.8Fe0.2PO4 cathode and the reduced metal dissolution in the electrolyte because of the easier and stronger binding between DTD and PF6- and the prioritized oxidation of DTD. The addition of DTD increased the capacity retention of the LiMn0.8Fe0.2PO4 cathode from 46.52 to 70.54% after 1000 cycles at 1 C over the voltage range of 3.0-4.5 V. Therefore, DTD is rendered as an effective electrolyte additive for engineering the cathode/electrolyte interface in favor of enhancing the performance of LiMn0.8Fe0.2PO4, providing a facile interfacial strategy to enhance the performance of LiMnPO4-based cathodes.

The undesirable capacity degradation of LiMnPO4 upon cycling at high temperatures is a challenge to its practical application. Herein, a lattice doping strategy is adopted to improve the high-temperature cycling stability of LiMnPO4, and the comparative study reveals that Al3+ doping into LiMnPO4 in a form of Li0.98Al0.02MnPO4 is highly beneficial to the cycling performance of LiMnPO4 and the capacity retention can be significantly improved from 67.4% to 93.4% after 100 cycles at 1 C at 60 oC, because Al3+ doping can effectively reduce passivation products deposition on the cathode and manganese dissolution in the electrolyte, which thus improve the cathode/electrolyte interface and stabilize the structure of LiMnPO4 at high temperatures.

The effect of alkali ions (Na+ and K+) on the hydrothermal synthesis of olivine lithium metal phosphates in the P excess system was investigated by taking the synthesis of LiMn0.8Fe0.19Mg0.01PO4 as a case study. It is found that the coexisting Na+ can compete with Li+ to partly form NaMnPO4 as an impurity when the Na+/Li+ ratio exceeds the critical value, and this is not the case for the coexisting K+. These behaviors should be related to the difference in the ionic size of the alkali ions which also leads to a very different process of LiMn0.8Fe0.19Mg0.01PO4 formation. The samples derived from the K+-coexisting reaction system can deliver much higher reversible capacities as compared with the sample derived from the Na+-coexisting reaction system. This study provides new insights into the chemistry of the hydrothermal synthesis of olivine lithium metal phosphates, with an important implication for controllable synthesis and property manipulation.

The addition of electrolyte additives is an effective strategy for tuning the property of the electrolyte to engineer the electrode/electrolyte interface, and there exist obvious discrepancies regarding the effect of fluoroethylene carbonate (FEC) as an electrolyte additive on the performance of cathodes. Herein FEC is introduced into the electrolyte of the LiMn0.8Fe0.2PO4/Li cell and its effect on the properties of the LiMn0.8Fe0.2PO4 is investigated. It is found that the addition of FEC in the electrolyte has a positive effect on the performance of the LiMn0.8Fe0.2PO4 cathode, which can be attributed to the reduced products generated by the interfacial side reactions on the LiMn0.8Fe0.2PO4 cathode surface and the decreased metal dissolution in the FEC-containing electrolyte, thanks to the higher oxidation resistance of FEC and the easier and stronger binding of FEC and PF6−.

Our previous work reported a new strategy based on a P excess reaction system to hydrothermally synthesize lithium transition metal phosphates (LiMPO 4 ), and herein the effect of P excess on the synthesis and property of LiMPO 4 is investigated in detail by taking the multi-component LiMn 0.8 Fe 0.19 Mg 0.01 PO 4 as a case. The results show that a proper degree of P excess is fairly profitable for hydrothermal synthesis including the effect on suppressing the occurrence of undesired Fe 2+ oxidation during synthesis and improving the particle dispersion of hydrothermal product, and thus the obtained samples have enhanced electrochemical performance. These effects of P excess should be general and applicable to hydrothermal synthesis of other lithium transition metal phosphates.

Cubic spinel LiNi0.5Mn1.5O4 is one of the most promising cathode materials for high energy density lithium ion batteries because of its higher voltage plateau at around 4.7 V vs Li+/Li. In this paper, LiNi0.5Mn1.5O4 spinels are synthesized with different lithium excess, and their composition, structure, morphology and electrochemical behavior are measured and compared. The results show that all samples have an ordered cubic spinel structure with Ni/Mn ordering in the octahedral sites, and the change of lithium excess can induce variations in phase composition and purity, Mn3+ amount, cation mixing and electrochemical behavior of the prepared LiNi0.5Mn1.5O4. Even with the least amount of Mn3+ and a higher amount of impurity, the sample with the least occupation of transition metal ions in the tetrahedral Li sites gives the best rate performance, justifying that the occupation of transition metal ions in the tetrahedral Li sites play a critical role in affecting the kinetics of lithium ion extraction/insertion for LiNi0.5Mn1.5O4 spinel.

Multicomponent olivine LiMn 0.8 Fe 0.19 Mg 0.01 PO 4 is hydrothermally synthesized in a Li-excess reaction system. Our synthesis experiments show that undesirable oxidation obviously occurs during synthesis in an air atmosphere, and the obtained product exhibits poor electrochemical performance. In contrast, undesirable oxidation can be effectively suppressed during synthesis in a N 2 atmosphere. Thus, the electrochemical performance of the hydrothermal product is significantly improved. When the hydrothermally synthesized LiMn 0.8 Fe 0.19 Mg 0.01 PO 4 is composited with carbon, increasing the sintering temperature from 600 to 700 °C can vastly improve the electrochemical performance of the composite, and a more continuous electron-conducting network can be formed in the LiMn 0.8 Fe 0.19 Mg 0.01 PO 4 /C composite when sucrose is used as the carbon source instead of carbon black. Thus, the composite derived from sucrose can exhibit better performance at a lower carbon content.

Here a series of Al-doped LiMnPO4 with controlled cation ratios based on appropriate charge compensation mechanisms are synthesized and compared. The results suggest that Al3+ can be doped into the lattice of LiMnPO4 and the preferable doping mechanism is in a scheme of Li1-xAlxMnPO4 where Al3+ occupies Li+ site with charge compensation by electronic defect. Such a charge-compensation mechanism is much different from those previously reported and needs further study. (C) 2019 The Electrochemical Society.

A new strategy based on the P excess reaction system is innovated to hydrothermally synthesize olivine phosphates (LiMPO4), and even unoptimized samples still show competitive electrochemical performance. Meanwhile, it is found that the presence of NH4+ in the P excess reaction system is detrimental to the efficient hydrothermal synthesis of LiMPO4.