Structure and Interface Design Enable Stable Li-Rich Cathode

Abstract

Li-rich layered-oxide cathodes have the highest theoretical energy density among all the intercalated cathodes, which have attracted intense interests for high-energy Li-ion batteries. However, O3-structured layered-oxide cathodes suffer from a low initial Coulombic efficiency (CE), severe voltage fade, and poor cycling stability because of the continuous oxygen release, structural rearrangements due to irreversible transition-metal migration, and serious side reactions between the delithiated cathode and electrolyte. Herein, we report that these challenges are migrated by using a stable O2-structured Li1.2­Ni0.13­Co0.13­Mn0.54­O2 (O2-LR-NCM) and all-fluorinated electrolyte. The O2-LR-NCM can restrict the transition metals migrating into the Li layer, and the in situ formed fluorinated cathode–electrolyte interphase (CEI) on the surface of the O2-LR-NCM from the decomposition of all-fluorinated electrolyte during initial cycles effectively restrains the structure transition, suppresses the O2 release, and thereby safeguards the transition metal redox couples, enabling a highly reversible and stable oxygen redox reaction. O2-LR-NCM in all fluorinated electrolytes achieves a high initial CE of 99.82%, a cycling CE of >99.9%, a high reversible capacity of 278 mAh/g, and high capacity retention of 83.3% after 100 cycles. The synergic design of electrolyte and cathode structure represents a promising direction to stabilize high-energy cathodes.

Surface Modification of Li‐Rich Mn‐Based Layered Oxide Cathodes: Challenges, Materials, Methods, and Characterization

“…The high resulting initial columbic efficiency and cycle efficiency of O 2 ‐type LMLO were attributed to the films formed by surface reactions of the fluorinated solvents, which avoid degradation by side reactions and suppress O 2 release upon initial cycling (Figure 10b). [ 177 ] In Figure 10c,d, the comparison of normalized voltage profiles upon discharge in the first and 100th cycles demonstrates that the voltage fading is effectively inhibited, owing to the use of the new electrolyte solution. In general, solutions that contain fluorinated solvents like FEC enable formation of effective passivating surface films of both negative and positive (high voltage) electrodes, due to elimination of HF, which forms very reactive intermediate species with double bonds.…”

“…[184] As each element has its own range of binding energy values, the response -intensity of Reproduced with permission. [177] Copyright 2020, American Chemical Society.…”

Designing positive electrodes with high energy density for lithium-ion batteries

“…For example, O2-type layered oxides LiTMO 2 and Li 1+x TM 1Àx O 2 (O2: lithium ions occupy octahedral sites in a close-packed oxide-ion array of ABCBA) mitigate TM migration due to TM-TM coulombic repulsion, which suppresses capacity fade and voltage decay during cycling. [250][251][252] In addition, a layered structure self-organizes upon cycling via coulombic attractions between ions and vacancies in Na 2Àx RuO 3 , which can effectively retain a large capacity. 253,254 Transition-metal vacancies can generate nonbonding O 2p states, leading to a highly reversible and stable oxygen-redox capacity, as reported for Na 2Àx Mn 3 O 7 .…”

Suppression of voltage-decay in Li2MnO3 cathode via reconstruction of layered-spinel coexisting phases

“…11,12 The voltage decay issue has been partially mitigated by several groups, nevertheless, a completely removal has not been reached yet. 13,14,15,16 For example, Y. S. Meng et. al minimized the voltage degradation of Li-rich layered Li 1.2 Ni 0.2 Mn 0.6 O 2 with micrometer-sized particles, leading to decreased surface area and increased structural mechanical stability.…”