Promises and Challenges of Next-Generation “Beyond Li-ion” Batteries for Electric Vehicles and Grid Decarbonization

Abstract

The tremendous improvement in performance and cost of lithium-ion batteries (LIBs) have made them the technology of choice for electrical energy storage. While established battery chemistries and cell architectures for Li-ion batteries achieve good power and energy density, LIBs are unlikely to meet all the performance, cost, and scaling targets required for energy storage, in particular, in large-scale applications such as electrified transportation and grids. The demand to further reduce cost and/or increase energy density, as well as the growing concern related to natural resource needs for Li-ion have accelerated the investigation of so-called "beyond Li-ion" technologies. In this review, we will discuss the recent achievements, challenges, and opportunities of four important "beyond Li-ion" technologies: Na-ion batteries, K-ion batteries, all-solid-state batteries, and multivalent batteries. The fundamental science behind the challenges, and potential solutions toward the goals of a low-cost and/or high-energy-density future, are discussed in detail for each technology. While it is unlikely that any given new technology will fully replace Li-ion in the near future, "beyond Li-ion" technologies should be thought of as opportunities for energy storage to grow into mid/large-scale applications.

Insights into Layered Oxide Cathodes for Rechargeable Batteries

“…This is a critical feature of Li x MO 2 compounds that gives them high capacity in a relatively narrow voltage window compared to other alkali compounds, as explained below. The effective interaction between intercalating ions increases significantly when larger alkali ions (e.g., Na + and K + ) are used in the layered structure [ 41 , 42 , 43 ]. These larger alkali ions increase the oxygen slab distance, reducing the oxygen charge density available for screening within the alkali layer [ 20 , 42 , 43 ].…”

“…The effective interaction between intercalating ions increases significantly when larger alkali ions (e.g., Na + and K + ) are used in the layered structure [ 41 , 42 , 43 ]. These larger alkali ions increase the oxygen slab distance, reducing the oxygen charge density available for screening within the alkali layer [ 20 , 42 , 43 ]. The larger effective repulsion between the Na + or K + ions affects the phase transition and electrochemistry in a very significant way as shown in Figure 2 b.…”

“…This phenomenon [ 44 , 45 ] becomes even more significant in K x CoO 2 [ 46 , 47 ]. The effect of the intercalant’s size on the phase transitions and voltage steps is not just limited to Co-containing compounds but is also generally applicable to other transition metal systems as described in a recent review [ 43 ].…”

“…Second, a simple argument shows that the average voltage slope is proportional to the effective interaction: V(x) is equal to − Li (x), and since Li (x) = , = − . In a simple regular solution model for mixing, this second derivative of the free energy is proportional to the effective interaction [ 41 , 43 , 49 ]. Hence, when the effective interaction is large, as in layered K x MO 2 compounds, the voltage curve has a high slope, limiting the achievable capacity between fixed voltage limits.…”

“…This analysis shows that the advantage of lithium systems in providing large capacity within reasonable voltage limits is in part due to the highly effective screening of the Li + -Li + interaction by oxygen. For Na, and in particular for K-ion based intercalation energy storage, it may be more advantageous to search among poly-anion compounds for good cathodes [ 43 ].…”