Study On The Improvement Of Structure And Electrochemical Performance Of Si Anode For Lithium-ion Batteries

Silicon, as lithium-ion battery anode material, it’s specific capacity is up to4200 m Ah·g-1, has the very high research value. But it’s large volume change in the process of charging and discharging badly influences the electrochemical properties of the battery,leading to the loss of electrical contact, capacity fading and eventually poor cycle performance. Studies have shown that the silicon particle size and electrode binder have a significant impact on the electrode electrochemical properties. This paper improves the cycle performance of the silicon anode by mixing micro and nano silicon powder, and using water-soluble sodium alginate as binder. X-ray diffractometer(XRD), scanning electron microscope(SEM), transmission electron microscope(TEM), photoelectron spectroscopy(XPS) were used to analysis the phase composition, crystal structure, microstructure and element content; The electrochemical properties were analyzed by Land testing system,electrochemical impedance spectroscopy(EIS) and cyclic voltammetry(CV). The research content is as follows.(1) Mixing the micro and nano silicon powder can improve the electrode cracking phenomenon. When the micro silicon powder and nano silicon powder were separately used as anode material, the electrode structure changed a lot after cycling; Micro silicon powder electrode has the highest first discharge specific capacity but poor cycle performance. The electrode impedance is big before cycling and changes much during cycling. The reversibility of lithiation/ delithiation processes is not that good. For the nano silicon powder electrode,both the first discharge specific capacity and cycle performance are very poor.The electrode impedance is big and the reversibility of lithiation/ delithiation processes is bad.When mix the micro and nano silicon powder according to the proportion of 8:2, the electrode structure is the most stable, the reversibility of lithiation/ delithiation processes is very good. The first discharge specific capacity reaches 3423.2m Ah g-1 with a first high coulomb efficiency up to 78%. The battery shows the best cycle performance, the discharge specific capacity is 1105.1 m Ah g-1 after 50 cycles.(2) Using the same amount of water-soluble sodium alginate and organic PVDF as binders separately, we compared the Si electrode electrochemical properties. The binder area coated on the Si particles reduces the ionic conductivity and electrical conductivity, influences the electrochemical properties of electrodes, leading to capacity attenuation. Less binder coated area means more silicon powder directly exposed in the electrolyte, providing more channels for ion transport, resulting in smaller electrode impedance. When the amount of sodium alginate is 10%, the first discharge specific capacity reaches 3424.2m Ah g-1 with a high coulomb efficiency up to 77.8%; the discharge specific capacity is 1010.9m Ah g-1 after50 cycles. When the amount of sodium alginate is 5%, the mechanical bond is not strong enough to maintain silicon electrode structure. When the mechanical bond is strong enough tomaintain the electrode structure, the less the binder, the better the electrochemical properties are.In conclusion, by mixing micro and nano silicon powder, using a suitable content of water-soluble sodium alginate as binder, this paper effectively improved the cycle performance and other electrochemical performances of silicon anode for lithium ion battery...