3 Li2MnSiO4 Preparation and electrochemical properties

Publié le 31 mars 2010 par high quanlity battery

Compared Li2FeSiO4, Li2MnSiO4 have a high theoretical capacity, but because of its low electronic conductivity caused by poor circulation and reversible defects hinder development. laptop battery And Li2FeSiO4 one-electron oxidation and reduction of the comparison, Li2MnSiO4 the Mn4 + / Mn2 + redox allows reversible insertion and extraction of two Li, theoretically get more than the capacity [7, 17-18].

Shackle [19] the first cathode material related to Portland to MnCl2, SiO2, LiOH as raw materials by liquid phase synthesis Li2MnSiO4, but the electrochemical properties of composite materials is not ideal. Dominko [13] through the modification of the sol-gel method, the Ar (containing 5% H2) atmosphere of 700 ℃ heat treatment after synthesis of the orthorhombic structure Li2MnSiO4 as cathode materials for lithium ion batteries. XRD diffraction peak broadening shows that the degree of crystalline material is not ideal, and there is impurity, impurity mainly MnO, also a small number of Li2SiO3 and another did not identify the phase. Also studied using electron diffraction crystal structure and found that the lattice constant b parameter is the XRD results of the two times that Li2MnSiO4 orthogonal to a distorted crystal structure. And to 1M LiPF6/EC-DMC (1:1) as electrolyte,Compaq Presario 2500 battery (compaq 2500 battery) electrochemical testing window for the 2.0-4.5V, at room temperature with a small current of C/30 charge and discharge the first discharge capacity achieved under the conditions of each chemical formula 0.6 Li's reversible embedding, but attenuated, poor cycling performance. Compared with Li2FeSiO4, lithium manganese silicate has a high charge and discharge voltage, lower conductivity. In order to improve its electrochemical performance, Dominko improved synthetic method to obtain a finer grain size and more uniform coating of carbon cathode materials to improve the electrical conductivity [20]. To 0.8M LiBOB / EC-DEC (1:1) as electrolyte, electrochemical window is 2.0-4.2V, the C/20 charge and discharge a small current conditions were tested at room temperature and 60 ℃ of the electrochemical performance. Because of their electrical conductivity of the electrolyte at room temperature has not been any improvement in performance; 60 ℃ can be achieved under the first charge of each chemical formula 1.5mol Li of prolapse, but the first discharge process can be reversible only 0.7mol Li embedding, and the decay is still fast. Further use of technology to improve the electrochemical properties of ball milling, ball milling the material was found slightly lower polarization, the reversible capacity increases. However,Compaq Presario 2100 battery (compaq 2100 battery) still unable to get a good cycle performance improvement, the capacity after 10 cycles from 140 mAh / g down to 100 mAh / g. XRD technique using different lithium deintercalation state Li2MnSiO4 crystal structure of the material found in the lithium-ion from Li2MnSiO4 gradual extrusion process, material changes in crystal structure, crystal features gradually disappear, the final structure completely collapsed, leading to capacity degradation. Thus, for low conductivity materials for Li2MnSiO4 not restrict the performance of the biggest obstacles, which may be the cathode material in Li's prolapse occurred in the course of the irreversible structural changes. By appropriate modification by doping may increase the structural stability Li2MnSiO4 materials, such as Li2MnxFe1-xSiO4 (x ≥ 0.5) could be achieved with more than one of each chemical type of reversible Li-ion deintercalation [21]. Yang Yong etc. using liquid phase of manganese acetate, lithium acetate, ferrous oxalate, and TEOS precursor was synthesized, and then mixed with sugar milling in N2 atmosphere at 600 ℃ after 10h were prepared Li2MnxFe1-doped compounds xSiO4 / C and Li2MnSiO4 / C composite cathode materials [7, 17, 22]. To 1M LiPF6/EC-DMC (1:1) as the electrolyte, the 1.5-4.8V voltage range for charge and discharge. In the 5 mAh / g current density Li2MnSiO4 / C charge capacity of the first material 310 mAh / g, the discharge capacity reached 209 mAh / g (theoretical capacity to reach 63% of the stoichiometric type 1.25 each electronic exchange); charge and discharge current density did not lead to large capacity attenuation rate with better performance, the current density of 150 mAh / g, the discharge capacity remained at 135 mAh / g. For Li2MnxFe1-xSiO4 / C materials, x = 0.5 compaq 319411-001 battery when the material has a higher specific capacity. In the 10 mAh / g in the first discharge capacity of the current density can reach 214 mAh / g (theoretical capacity of 86%, 1.29 for each type of chemical metering electronic exchange). But Li2MnxFe1-xSiO4 / C (except x = 0) and Li2MnSiO4 / C cathode materials have shown poor cycling performance, after 10 cycles Li2MnSiO4 / C from 209 mAh / g decreased to 140 mAh / g, Li2MnxFe1-xSiO4 / C (x = 0.5) from 214 mAh / g decreased to 130 mAh / g. The study concludes with Dominko consistent, Li2MnSiO4 / C in the process of charging structure will collapse occurred, and to amorphous transition, there have been irreversible cycle of poor performance resulted in structural changes.

4 Li2CoSiO4 Preparation and electrochemical properties

Christopher Lyness first reported Li2CoSiO4 cathode materials were synthesized by three kinds of different crystal Li2CoSiO4 material [23]. First of all, prepared by hydrothermal method II-Li2CoSiO4, and then in air treatment at 700 ℃ 2h obtained I-Li2CoSiO4. 0-Li2CoSiO4 is through II-Li2CoSiO4 at 1100 ℃ heat down to 850 ℃ after 2h and then quenched to room temperature and obtained. These three kinds of different crystal Li2CoSiO4 8:2 ratio and superconducting materials mixed carbon milling to improve the material's conductive properties. 1M LiPF6/EC-DMC (1:1) as electrolyte, at 50 ℃, 2.0-4.6V voltage range for charge and discharge. At 10mA / g current density, II-Li2CoSiO4 / C materials, the first charge capacity of 180 mAh / g and discharge capacity only for 30 mAh / g, decay rapidly, the capacity after 10 cycles largely ignored. Other two kinds of crystal structure Li2CoSiO4 materials and II-Li2CoSiO4 / C similar, I, 0 the first charge capacity was 80 mAh / g and 100 mAh / g, the discharge capacity only for 30 mAh / g, 10 cycles after the basic capacity can be ignored. To further improve the carbon-coated Li2CoSiO4 / C material properties. Hydrothermal synthesis in the process of adding carbon gel after argon treatment at 700 ℃ for 2h obtained I-Li2CoSiO4 / C material, Hp F4812A battery the first charge and discharge capacity was 170 mAh / g and 60 mAh / g, 10 cycles After the discharge capacity of 40 mAh / g. Yang Yong etc. were used and the liquid phase hydrothermal synthesis Li2CoSiO4 [24]. Exist in liquid phase synthetic materials Co3O4 impurities, and hydrothermal method there are two kinds of access to material impurities. Liquid cathode materials obtained by the first electrochemical cycle, only 0.26 times the reversible deintercalation of lithium ion, carbon coated surface after a 0.46-fold reversible lithium ion deintercalation; hydrothermal synthesis obtained cathode material, the first electrochemical cycle of 0.41 times in reversible deintercalation of lithium ions, and Christopher Lyness reported similar to the first cycle irreversible capacity were greater, attenuation soon. A theoretical calculation also shows that Li2CoSiO4 higher than Li2MnSiO4 de intercalation voltage, while other properties are poor [25]; calculated Na doping could improve the material's electrochemical performance and reduce the band gap materials, an increase of conductivity with the electron density, improve the electronic conductivity and increased cell volume, the expansion of lithium ion diffusion in the lattice channels, more conducive to lithium extrusion [26].

5 Conclusion and Outlook

Li2MnSiO4 Department of lithium-ion battery cathode materials for environmental protection, low cost, security and good benefits, with a wide range of research value and application prospect, it is worth exploring in depth systematic study, to further improve the performance of such materials. At present the following main research directions:

(1) small particle size and phase structure of pure Synthesis Li2MnSiO4. At present, most researchers silicate synthesized cathode material contains impurities, to obtain the pure phase material for improving the electrochemical properties of the material is still very important. Also need to study the synthesis method to improve the material's size and its distribution. Reduce and control the uniformity of particle size distribution on diffusion controlled anionic polymer material is extremely beneficial to be able to effectively reduce the diffusion path of lithium ion to improve the electrochemical performance.

(2) Li2MnSiO4 lower electronic conductivity improvement. Carbon surface coating technology to improve the conductivity of the practical ways to further study, Hp F4809A battery to obtain uniform distribution of carbon materials, carbon and active material to improve the surface contact state, to improve the electrochemical properties of the material.

(3) are silicate materials during charge and discharge the complex structural changes in-depth study to understand the mechanism which changes. Further research by Li2MnSiO4 (M = Fe, Mn, Co) solid solution formation between the three other methods such as ion doping to improve the bulk material structure, doped and mixed ion by lysosomal synergies to improve the conductivity of materials and its structural stability, in order to obtain high-capacity long life silicate series of cathode materials.

(4) Select the match with the electrolyte, anode and the active role of material circumstances between the surface and interface phenomena, to obtain more suitable electrolyte system, to reduce the attenuation of active substances, to improve the cycling performance, rate capability and safety sex.

In summary,Hp F4098A battery because of their own environment-friendly, excellent safety performance, low cost, and the changing structure of silicate also has adjustable features, Li2MnSiO4 polyanionic materials can have greater potential to become the next generation of security, low-cost lithium-ion battery cathode material, is expected to apply in electric cars, solar energy storage and emergency power supply side.