The silicon (Si) based anode material has a high theoretical specific capacity (4200 mAh/g) and is suitable for the lithium-ion platform. It is an ideal high-capacity anode material for lithium ion batteries. During the charging and discharging process, the volume change of Si reaches more than 300%, and the internal stress generated by the severe volume change easily causes the electrode to be powdered and peeled off, which affects the cycle stability.
In lithium ion batteries, the binder is one of the important factors affecting the stability of the electrode structure. According to the nature of the dispersion medium, the lithium ion battery binder can be classified into an oily binder using an organic solvent as a dispersing agent and an aqueous binder using water as a dispersing agent. Liu Xin et al reviewed the research progress of binders for ruthenium capacity negative electrode. It is believed that the application of polyvinylidene fluoride (PVDF) modified binder and aqueous binder can improve the electrochemical performance of high capacity anodes, but There is no discussion or comparison of binders for silicon based anodes.
The authors reviewed the research progress of silicon-based anode material binders and compared the advantages and disadvantages of different types of binders.
1. Oily binder
Among the oily binders, the homopolymers and copolymers of PVDF are the most widely used.
1.1 PVDF homopolymer adhesive
In the large-scale production of lithium ion batteries, PVDF is generally used as a binder, and an organic solvent N-methylpyrrolidone (NMP) or the like is used as a dispersing agent. PVDF has good viscosity and electrochemical stability, but electron and ion conductivity is poor, organic solvent is volatile, flammable, explosive and toxic; and PVDF is only connected to silicon-based anode material with weak van der Waals force, and can not adapt to Si Dramatic volume changes. Conventional PVDF is not suitable for silicon-based anode materials [3 -5].
1.2 PVDF modified binder
In order to improve the electrochemical performance of PVDF applied to silicon-based anode materials, some scholars have proposed modification methods such as copolymerization and heat treatment. ZH Chen et al found that the terpolymer polyvinylidene fluoride-tetrafluoroethylene-ethylene copolymer [P(VDF-TFE-P)] can enhance the mechanical properties and viscoelasticity of PVDF. J. Li et al found that heat treatment at 300 ° C under argon gas protection can improve the dispersion and viscoelasticity of PVDF. The modified PVDF/Si electrode was cycled 50 times at 150 mA/g at 0.17 ~ 0_90 V with a specific capacity of 600 mAh/g. Although the PVDF/Si electrode has been modified, the cycle performance is improved, but the cycle stability is still not satisfactory.
2, water-based binder
Compared with oily binders, water-based binders are becoming more environmentally friendly, cheaper and safer to use, and are gradually being promoted. The currently studied silicon-based anode material binders are aqueous binders such as sodium carboxymethyl cellulose (CMC) and polyacrylic acid (PAA).
2. 1 styrene butadiene rubber (SBR) / carboxymethyl fiber sodium (CMC) binder
SBR/CMC has good viscoelasticity and dispersibility and has been widely used in the scale production of graphite anodes. W. R Liu et al found that the (SBR/CMC)/Si electrode can be charged and discharged in a constant capacity of 1 〇〇〇mAh/g (0 ~ 1.2 V) 60 times, and the electrochemical performance is better than that of PVDF/Si electrode, but 60 The secondary cycle does not fully explain the cycle stability.
2.2 CMC binder
Compared with SBR/CMC and PEAc/CMC with better viscoelasticity, it is considered that the inelastic CMC binder is more suitable for silicon-based anode materials. J. Li et al [7] found that the CMC/Si electrode is cycled 70 times at 150 mA/g at 0•17 ~0. 90 V, with a specific capacity of 1 100 mAh/g, which is better than (SBR/CMC)/Si and PVDF/Si electrode. B. Lestriez et al. [8] found that the electrochemical performance of the CMC/Si electrode is better than that of the (PEAA/CMC)/Si electrode because PEAA tends to agglomerate the carbon black and affect the cycle stability of the electrode.
The carboxymethyl group of CMC can be bonded to Si through a chemical bond (covalent bond or a bond), and has a strong bonding force to maintain the connection between Si particles; and CMC can form a solid electrolyte phase interface film (SEI) on the surface of Si. The coating inhibits the decomposition of the electrolyte.
Although the electrode exhibits good electrochemical performance when CMC is used as a binder, the electrode ratio, pH value and CMC substitution degree (DS) affect the electrochemical performance of the CMC/Si electrode to varying degrees. JS Bridel et al [12-14] found that when m(Si):m(C): CMC binder has a good application prospect, but CMC has general viscosity and brittleness and poor flexibility. The pole piece is easy to crack when charging and discharging [13], and CMC is greatly affected by the electrode ratio and pH value. Related research remains to be seen. 2.3 PAA binder PAA has a simple molecular structure, is easy to synthesize, and is soluble in water and some organic solvents. Studies have shown that PAA with higher carboxyl content is more suitable for silicon-based anode materials than CMC [15%. Nine Magasinski et al. [15] found that PAA not only forms a strong hydrogen bond with Si, but also forms a more uniform coating on the Si surface than CMC. The PAA/Si electrode is C/2 at 0•01 ~ 1. 00 V. Cyclic 100 times, the specific capacity is 2 400 mAh / g0 S. Komaba et al [16] found that: PAA distribution in the pole piece is more uniform, can form a similar SEI film coating on the Si surface, inhibit electrolyte decomposition, excellent performance In CMC, polyvinyl alcohol (PVA) and PVDF. M. Hasegawa et al. believe that although PAA containing a large amount of carboxyl groups has good viscosity, the carboxyl group is hydrophilic, and easily reacts with residual moisture in the battery to affect performance. If the electrode still has hydroxyl or water, it will react with LiPF6 in the electrolyte to decompose PF5 (>60 1C), which will decompose the organic solvent and affect the charge and discharge performance of the electrode. If the PAA is vacuum heat treated at 150 - 200 t for 4 ~ 12 h, the carboxyl moiety of PAA is condensed, which not only reduces the hydrophilicity of the electrode, but also enhances the structural stability of the electrode [1^7]. B. Koo et al. heat treated CMC and PAA for 2 h at 150 t:, and obtained the c-CMC-PAA/Si electrode at a cycle of 1. 5 A/g at 0_005 ~ 2. 000 V for 100 times. 1 500 mAh/g. 2.4 sodium alginate binder The structure of sodium alginate is similar to that of CMC, and the arrangement of carboxyl groups is more regular. I. Kovalenko et al [20] used sodium alginate as a binder for a silicon-based anode material, and prepared a sodium alginate/Si electrode at a cycle of 4. 2 A/g at 0.01 to 1.00 V for 100 times, with a specific capacity of 1 700 mAh/g, better than CMC/Si and PVDF/Si electrodes. At present, there are few reports on sodium alginate, and similar to PAA, sodium alginate has a high carboxyl group content and has a problem of strong hydrophilicity. 2.5 Conductive polymer binder The conductive polymer binder has both viscosity and electrical conductivity, and can improve the electrical conductivity while maintaining the stability of the pole piece structure. G. Liu et al. [21] used poly(9,9-dioctylfluorene-co-fluorenone-co-methylbenzoic acid) (PFFOMB) for silicon-based anode materials, and prepared PFF0MB/Si electrodes with C/ 10 cycles 650 times from 0.01 to 1.00 V with a specific capacity of 2 100 mAh/g. H. Wu et al [22] in situ synthesized, prepared polyaniline (PAni) / Si electrode, cycled at 0.00 A / g at 0.01 - 1.00 V 5,000 times, the specific capacity is still 550 mAh / g. 2.6 Other binders In addition to the above binders, binders such as carboxymethyl chitosan, polyacrylonitrile (PAN) and PVA can also be used for the silicon-based negative electrode material.竣Methyl chitosan/Si electrode is cycled 50 times at 500 mA/g at 0. 12 ~ 1. 00 V, specific capacity is 950 mAh/g[s], PAN/Si electrode and PVA/Si electrode are at C/ 2 Cycled 50 times from 0.005 to [3] 000 V, and the specific capacity was maintained at 600 mAh/g 124-251. Although the above binders can form a strong hydrogen bond with Si and have good cycle stability, the cycle stability is slightly inferior to those of CMC, PAA and sodium alginate. 3. Conclusion The development and application of adhesives is one of the effective ways to improve the cycle stability of silicon-based anode materials for lithium-ion batteries. The use of PVDF modified binder or aqueous binder can improve the cycle stability and electrochemical performance of the silicon-based anode to some extent. Different types of binders have their own advantages and disadvantages. Relatively speaking, PAA, sodium alginate and conductive polymer binders exhibit better cycle stability and electrochemical performance when applied to silicon-based anode materials. The development of an aqueous binder capable of forming a strong chemical bond and a relatively uniform coating with Si is an important development direction of a silicon-based negative electrode material binder. In addition, conductive polymer binders with both viscous and conductive properties also have broad application prospects.
The low-voltage transformer mainly uses the principle of electromagnetic induction to change the AC voltage. Its main functions are voltage conversion, current conversion, impedance conversion, isolation, and voltage stabilization. The low voltage transformer is the transformer below 600V. Low-voltage transformer is composed of three parts: primary coil, secondary coil and iron core (magnetic core). It is usually used in electrical equipment and wireless circuits as a tool for raising and lowering voltage, matching impedance, and safety isolation.
Classification of low-voltage transformers
2. According to the purpose, it is divided into control transformer, local lighting transformer, isolation transformer, rectification transformer, etc.
3. According to the coil winding method, it can be divided into foil winding, wire winding, etc.
4. According to the protection mode, it can be divided into: with enclosure, without enclosure, etc.
Low Voltage Transformer,Auto Transformer 380V,Transformer 380V To 220V,Single Phase To 3 Phase Transformer
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