(Invited) Maximizing Energy Density of Lithium-Ion Batteries Using Pre-Lithiation Strategies

Next generation lithium-ion batteries (LIBs) with higher energy density adopt some novel anode materials such as low potential intercalation-type, conversion-type, and alloying-type materials. They have the potential to exhibit higher capacity, superior rate performance as well as better cycling durability than conventional graphite anode, while on the other hand always suffer from larger initial irreversible capacity loss (ICL) in the first several cycles. The huge initial ICL inevitably results in decreased energy density of full cell when pairing with cathode materials, which hinders the commercialization of next generation LIBs. During the last two decades, various pre-lithiation strategies are developed to mitigate the initial ICL by presetting the extra lithium sources into cathode, anode and/or electrolyte, which effectively improve the first coulombic efficiency and thus higher energy density as well as better cyclability [1]. In this presentation, we are going to discuss how to achieve a maximum energy density from theoretical and experimental aspects.

At first, we will provide a theoretical specific energy of LIBs with and without pre-lithiation. The specific energy of a LIB with coulombic efficiency of ε due to the initial ICL has been derived and can be expressed as:

E=V/[1/c_a+1/c_c+(1-ε)/(εc_ad)]

where, the specific energy is calculated based on electrode materials only, V is the average cell voltage, c_a and c_c are reversible specific capacities of anode and cathode, respectively, c_ad is the specific capacity of material to be used for compensating initial ICL from anode, it can be extra cathode loading or highly concentrated lithium source, called additive material. The specific energy can also be expressed as:

E=c_cell V F

where c_cell is the specific capacity of LIB cell and can be obtained from 1/c_cell=1/c_a+1/c_c, F=c_ad-eff/(c_ad-eff+c_cell) and c_ad-eff=ε c_ad/(1-ε). The F represents the reduction factor of specific energy from the maximum value due to the initial ICL. The relationships of the specific energy to the coulombic efficiency and the specific capacity of additive material will be discussed in detail.

Then, we will review four types of pre-lithiation strategies, including lithium source in anode, lithium source in cathode, sacrificed electrode method, and extra lithium source [2]. The main properties of required assembly condition, controllability, scalability, and the effect to the energy density of full cells for these pre-lithiation strategies will be carefully compared. Particularly, battery system using Si-based anode and sulfur based cathode will be discussed in detail. In general, all the current pre-lithiation strategies still face different challenges.

Finally, we will layout the current challenges and future perspectives. This presentation also aims to bring up new insights to reassess the significance of pre-lithiation strategies for the next generation LIBs and offer a guideline for the research directions based on the proposed pre-lithiation strategies.

References:

[1] K. Yao, R. Liang, and J.P. Zheng, Journal of Electrochemical Energy Conversion and Storage, Vol. 13, 011004 (2016).

[2] Shellikeri, V. Watson, D. Adams, E. E. Kalu, J. A. Read, T.R. Jow, J.S. Zheng, and J.P. Zheng, Journal of The Electrochemical Society, 164, A3914-A3924 (2017).