Rice husks (RHs) are rich in silica and organic carbon components, which have been widely applied in lithium ion batteries. However, the natural structure of uneven dispersion between SiO 2 and amorphous C in RHs leads to poor electrical conductivity and structural integrity. In this work, SiO 2 /C composites were prepared by mechanical mixing and high-temperature carbonization from RHs, with coal tar electronic pitch (CTEP) or polyvinyl chloride (PVC) as the carbon coating agent, which imparted some improvement in cycling performance, initial coulombic efficiency (ICE), and rate performance. Compared with the high electrical conductivity of CTEP, PVC with low viscosity coated uniformly the surface of BM-SiO 2 /C, which is beneficial to providing both elastic and mechanical stability and keeping the structural integrity. BM-SiO 2 /C-PVC-6 exhibits a more stable cycling performance and higher specific capacity of 730 mA h g -1 after 100 cycles at 0.1 A g -1 , with the ICE of 60%. Hence, the application of carbon coating agent plays a vital role in improving the electrochemical performance of SiO 2 /C composites. PVC with excellent coating performance was selected to coat RHs-SiO 2 /C and the electrochemical performance was enhanced, which provides a method of converting biomass material into a useful storage device.
Caiyan Shen,Huinan Yu,Zhiyuan Xue,Guorong Hu,Yanbing Cao,Zhongdong Peng,Ke Du
LiMn 2 O 4 is considered to be a promising cathode material for lithium-ion batteries due to its decent energy density, low price and environmental benignity. However, the problems of Mn dissolution, migration and deposition during the cycle, seriously affect its lifespan, especially at high temperature. In this study, we developed a strategy by which we killed two birds with one stone. A low molecular weight polyacrylic acid (PAA) mixed with sodium carboxymethyl cellulose (CMC) is applied as binder and coating agent for cathode particles at the same time. The conventional and environmental unfriendly polyvinylidene difluoride (PVDF)-N-methylpyrrolidone (NMP) system is replaced by the cheap and green aqueous binder with improved adhesive effect. Furthermore, the binder-based surface coating layer not only alleviates the side reaction between the electrolyte and the cathode particles, but also chelates the dissolved Mn 2+ by the large amount of carboxyl groups in PAA molecules and so prevents the following migration and deposition of Mn 2+ . In the button half-cell with low molecular weight PAA based binder, the capacity retention reaches 94.1 % after 1000 cycles at room temperature and 92.0 % after 200 cycles at 60 degrees centigrade. Meanwhile, 18650-type cylindrical cells were prepared with this binder, which shows a great high temperature storage performance. After the cell was held at 60 degrees centigrade for 25 days at full charged state, the internal resistance increased by only 1.25mΩ, the voltage decreased by only 0.1 V, the residual capacity retention and recovery capacity retention reaches 85.6 % and 92.2 %. This work shows the great potential of the aqueous binder in dealing with the problem of Mn dissolution during the cycling of manganese-based cathode materials for lithium-ion batteries.
The prevalent synthesis of colloidal metal oxide nanocrystals relies on the synthesis of various precursors, such as organometallic compounds, which are usually sensitive to moisture or oxygen and generally expensive. Based on the economic efficiency, the costs of the starting materials and synthetic process should be addressed. Herein, a general simple synthetic procedure from inexpensive and nontoxic precursors is developed. Under optimized reaction conditions, MnO nanocrystals are synthesized with commercially purchased bulk manganese oxides as starting materials, such as MnO, MnO2, and Mn3O4. The size and morphologies of nanoparticles are modulated by tuning the types and dosage of coating agents. Moreover, this synthetic strategy is further extended to other nanoparticles including Fe3O4 nanocrystals and FeMnOx nanocrystals. Furthermore, Re doped MnO nanocrystals exhibiting fluorescence properties have been synthesized with this method, which endows the fluorescence properties to these oxide nanocrystals.
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