Pre‐Lithiation of Silicon Anodes by Thermal Evaporation of Lithium for Boosting the Energy Density of Lithium Ion Cells

Abstract

Silicon (Si) is one of the most promising anode candidates to further push the energy density of lithium ion batteries. However, its practical usage is still hindered by parasitic side reactions including electrolyte decomposition and continuous breakage and (re‐)formation of the solid electrolyte interphase (SEI), leading to consumption of active lithium. Pre‐lithiation is considered a highly appealing technique to compensate for active lithium losses. A critical parameter for a successful pre‐lithiation strategy by means of Li metal is to achieve lithiation of the active material/composite anode at the most uniform lateral and in‐depth distribution possible. Despite extensive exploration of various pre‐lithiation techniques, controlling the lithium amount precisely while keeping a homogeneous lithium distribution remains challenging. Here, the thermal evaporation of Li metal as a novel pre‐lithiation technique for pure Si anodes that allows both, that is, precise control of the degree of pre‐lithiation and a homogeneous Li deposition at the surface is reported. Li nucleation, mechanical cracking, and the ongoing phase changes are thoroughly evaluated. The terms dry‐state and wet‐state pre‐lithiation (without/with electrolyte) are revisited. Finally, a series of electrochemical methods are performed to allow a direct correlation of pre‐SEI formation with the electrochemical performance of pre‐lithiated Si.

Revealing the Role, Mechanism, and Impact of AlF3 Coatings on the Interphase of Silicon Thin Film Anodes

“…[2] In this respect, there is still room for further improvements, as silicon (Si) holds greater promise as an anode material compared to state-ofthe-art (SOTA) graphite materials due to the almost 10-fold increase in specific capacity, low delithiation potential (≈0.4 V vs. Li|Li + ), and low-cost precursor materials. [3] Si experiences a series of phase transitions when alloying with Li (formation of several intermetallic phases), offering a maximum gravimetric capacity of 3579 mAh g −1 for the Li 15 Si 4 phase. [4] Despite the perceived advantages, the commercialization of Si-rich (the so-called Si-dominant) anodes for high-energy LIB cells is still challenging.…”

Constructing a Yolk–Shell Structure SiOx/C@C Composite for Long-Life Lithium-Ion Batteries

“…10,11 Nevertheless, the enormous volume changes of silicon materials in repeated galvanostatic discharge/charge processes lead to the rapid attenuation of capacity and even cause safety problems, which seriously restricts the commercial application of silicon-based LIBs. 12,13 In addition, silicon-based materials are a common semiconductor material which has poor electrical conductivity. Therefore, improving the conductivity of silicon electrodes is necessary even if this strategy may offset the superiority of high capacity.…”

“…Energy depletion and environmental pollution have gradually become major problems that cannot be ignored in today’s world, while the pursuit of sustainable development is meaningful. − At present, consumers focus on green new energy storage technologies and devices represented by lithium-ion batteries (LIBs), which are usually used in 3C electronics on account of their advantages of high operating voltage, long service life, and environmental friendliness. − Conventional commercial LIBs based on graphite anodes are unable to match the need for high energy density, which suffer from limited theoretical specific capacity (372 mAh g –1 ). − On this basis, silicon-based anodes have become the most potential substitute for commercial graphite anodes in the future because of their high theoretical specific capacity (∼4200 mAh g –1 ) and suitable operating voltage (<0.5 V vs Li/Li + ). , Nevertheless, the enormous volume changes of silicon materials in repeated galvanostatic discharge/charge processes lead to the rapid attenuation of capacity and even cause safety problems, which seriously restricts the commercial application of silicon-based LIBs. , In addition, silicon-based materials are a common semiconductor material which has poor electrical conductivity. Therefore, improving the conductivity of silicon electrodes is necessary even if this strategy may offset the superiority of high capacity. , …”

On the Practical Applicability of the Li Metal‐Based Thermal Evaporation Prelithiation Technique on Si Anodes for Lithium Ion Batteries

“…[31][32][33] However, the inhomogeneous Li distribution within the electrode should be taken into account when applying this technique, [34] as the cells will experience self-discharge and unintentional aging behavior. [35] To overcome these issues, we recently developed a Li thermal evaporation technique on Si thin films to facilitate uniformly lateral and in-depth Li distributions. [35] Prelithiation by Li thermal evaporation overcomes the above-mentioned challenges using passivated Li metal powder, i.e., avoiding direct handling with Li metal powder, the ability to precisely control the degree of prelithiation, and ensuring highly homogeneous Li metal distribution at the electrode surface.…”

“…[35] To overcome these issues, we recently developed a Li thermal evaporation technique on Si thin films to facilitate uniformly lateral and in-depth Li distributions. [35] Prelithiation by Li thermal evaporation overcomes the above-mentioned challenges using passivated Li metal powder, i.e., avoiding direct handling with Li metal powder, the ability to precisely control the degree of prelithiation, and ensuring highly homogeneous Li metal distribution at the electrode surface. [34] In our previous study, the capacity retention was notably improved with up to 70% state-of-health after 200 cycles due to "pre-SEI formation" and homogeneous Li-Si alloying reaction.…”