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

Abstract

fossil fuel-free society. [1,2] Further developments in the whole battery value chain and across all technology readiness levels are needed to fulfill the demand for batteries with increased energy density and fast charging capability, lower cost, and higher safety. [3,4] With regard to the negative electrode (anode), so-called "alloyingtype" materials such as tin and silicon have become promising candidates to replace state-of-the-art (SOTA) graphite in future LIBs because they can reversibly store nearly four lithium ions per host atom offering much higher energy densities. [5][6][7] Si has become more attractive than Sn most likely due to the lower cost, greater availability, and higher capacity. [8][9][10] In theory, the specific capacity that can be achieved with Si is up to 3579 mAh g −1 combined with a low average delithiation potential (≈0.4 V vs Li|Li + ) and low voltage hysteresis. [11] Despite all these advantageous characteristics, the practical use of Si-based anode materials in commercial LIB cells faces major challenges, i.e., enormous particle stress on the atomic scale which leads to particle fracture and detachment from the current collector on the electrode scale. [12] In addition, continuous (re-)formation of the solid electrolyte interphase (SEI) causes ongoing active lithium losses (ALL) and Lithium ion batteries (LIBs) using silicon as anode material are endowed with much higher energy density than state-of-the-art graphite-based LIBs. However, challenges of volume expansion and related dynamic surfaces lead to continuous (re-)formation of the solid electrolyte interphase, active lithium losses, and rapid capacity fading. Cell failure can be further accelerated when Si is paired with high-capacity, but also rather reactive Ni-rich cathodes, such as LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM-811). Here, the practical applicability of thermal evaporation of Li metal is evaluated as a prelithiation technique on micrometer-sized Si (µ-Si) electrodes in addressing such challenges. NCM-811 || "prelithiated µ-Si" full-cells (25% degree of prelithiation) can attain a higher initial discharge capacity of ≈192 mAh g NCM-811−1 than the cells without prelithiation with only ≈160 mAh g NCM-811−1. This study deeply discusses significant consequences of electrode capacity balancing (N:P ratio) with regard to prelithiation on the performance of full-cells. The trade-off between cell lifetime and energy density is also highlighted. It is essential to point out that the phenomena discussed here can further guide the direction of research in using the thermal evaporation of Li metal as a prelithiation technique toward its practical application on Si-based LIBs.

Stress Mitigation of Nanosilicon Anode to Achieve Energy‐Dense and Highly‐Stable Full Cell

“…[42] In the Si-Cu||LiFePO 4 full cell (Figure 3G), the ICE is 84% and the reversible cathode capacity is 146.8 mAh g −1 at 0.5 C. The energy density is calculated to be 463 Wh kg −1 , which is higher than that of commercial graphite-based and previously reported Si-based full cells. [43][44][45] After 500 cycles at a high rate of 2 C, the cathode retains a capacity of 101.1 mAh g −1 with an 81% retention and a CE of nearly 100%. Figure 3H compares the electrochemical performance of Si-based full cells, with detailed information provided in Table S2 (Supporting Information).…”

Li2SiF6 In Situ Embedded in an Amorphous SiO Matrix to Inhibit Volume Expansion during Prelithiation

“…However, the process of disassembly and reorganization of batteries is not suitable for large-scale commercial production and can be applied only to small-scale scientific research. Direct contact prelithiation mainly includes the addition of stabilized lithium metal powder supplement lithium, , lithium-related alloys supplement lithium, lithium thermal evaporation supplement lithium, − lithium foil supplement lithium − and so on. Although the degree of prelithiation can be controlled by controlling the addition of stabilized lithium metal powder and lithium-related alloys, their high chemical activity makes them difficult to be compatible with traditional electrode pastes and solvents, and there are certain safety issues in large-scale applications.…”

Built-In Electric Field Generated by the Piezoelectric Effect Facilitates a High Li+ Diffusion Rate for Li-Ion Batteries

“…Silicon (Si) anode has functioned as one of the most potential candidates for its large theoretical capacity of 4200 mAh·g –1 , relatively low discharge potential plateau (∼0.4 V vs Li/Li + ) and large elemental abundance on the earth. − However, Si-based anode still sustains challenges such as mechanical fracture of Si particles, irreversible electrode–electrolyte side reactions, and rapid capacity degradation due to dramatic volume expansion of Si anode, which greatly hinders the Si anode application in LIBs. − …”