We investigated how the pre-doping methods affected the structures and the electrochemical properties of silicon. Moreover, the capacity decreased considerably as the number of cycles increased. In contrast, the LiNCM electrode paired with a pristine silicon anode lost 15% of its capacity because the charging of silicon is not reversible. The capacity of the cell containing a pre-doped silicon anode was consistent with the theoretical value for LiNCM of 150 A h/kg. The anode/cathode balance of the full cells was set to 1.0 assuming that apparent capacity of silicon is 2500 mA h/g-Si by adjusting the amount of silicon on anode and that of LiNCM on cathode. The cycle performance indicated the quality of the SEI formed in the pre-doping process.įigure 2 shows the charge and discharge curves of full cells containing either a silicon anode electrochemically pre-doped under pressure or a pristine silicon anode with a LiNCM cathode for the first five cycles. The electric charge consumed for SEI formation was quantified by the total charge during the pre-doping process and in the first charging process. The charge capacity of the pre-doped silicon anode in the first cycle shows the amount of intercalated and removable free lithium besides that consumed to form the SEI. We describe the properties and structure of a silicon anode electrochemically pre-doped under pressure. Furthermore, the pressure relaxes the transformation strain of the silicon anode during pre-doping in a controlled manner that avoids the collapse of the silicon fine structure. The electrochemical reaction during pre-doping with electrolyte additives produces a high-quality SEI. This study proposes a pre-doping process for silicon anodes, in which electrochemical pre-doping under pressure produces the SEI on the surface of silicon particles. These methods are unsuitable for industrial-scale production and remain at the laboratory scale. The second is limiting the voltage range during battery operation to keep the volume change small, which improves the cycle life at the expense of the capacity 13, 14, 15. The first is using a binder, particularly durable binders, such as polyimides 11 or styrene-butadiene rubber 12 to maintain the size of silicon particles, but the method requires complicated pretreatments. Two main solutions to overcome these problems have been proposed. This process destroys the silicon particles completely before the SEI layer is fully formed on their surfaces. The intercalation causes the expansion and collapse of the silicon particles, continuously exposing new surfaces where the SEI is formed. The formation of a stabilized SEI is still challenging because in conventional pre-doping methods, such as contact or electrochemical pre-doping, some of the lithium doping forms the SEI on the surface of silicon particles, and the rest of the lithium intercalates into the silicon particles. The SEI provides an inactivated and stabilized conductive pathway for lithium ions and not for electrons, and is even impenetrable to the electrolyte, which prevents further growth of the SEI 9, 10. The SEI is important in silicon anodes because it allows the steady intercalation and desorption of lithium through the surface of the silicon particles. The large surface area of nanostructured silicon should produce irreversible capacity caused by the formation of a solid electrolyte interface (SEI) passivation layer 8. Various types of silicon nanoparticles 3, 4, 5 and nanowires 6, 7 have shown longer cycling lives than micron-sized particles. The high capacity of silicon causes a large expansion of electrode volume of up to 300–400%, leading to the collapse of fine particle structures, and thus causing a dramatic decline in cycle performance. In the reaction mechanism of silicon during charging and discharging, the phase transition from the crystalline to amorphous state proceeds via the formation of a lithiated amorphous silicide in the initial discharging stage, followed by the formation of Li 15Si 4 in the deep discharging stage 2. To solve this problem, silicon is an attractive anode material for the next generation of LIBs due to its high capacity of 3572 mA h/g 2, which is approximately 10 times larger than that of graphite (372 mA h/g). Rechargeable lithium-ion batteries (LIBs) are integral to these sophisticated devices however, a serious drawback is that their energy density and capacity density have not increased substantially 1. An increasing number of intelligent devices, electric vehicles, and smart energy management systems are being used in all parts of society, and this growing market, especially in mobility and transportation, requires low-cost rechargeable batteries with high energy density.
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