Novel polymer coating for chemically absorbing CO2 for safe Li-ion battery

Abstract

Gas evolution in Li-ion batteries remains a barrier for the implementation of high voltage materials in a pouch cell format; the inflation of the pouch cell is a safety issue that can cause battery failure. In particular, for manganese-based materials employed for fabricating cathodes, the dissolution of Mn 2+ in the electrolyte can accelerate cell degradation, and subsequently gas evolution, of which carbon dioxide (co 2) is a major component. We report on the utilization of a mixture of polymers that can chemically absorb the co 2 , including the coating of aluminum foils, which serve as trapping sheets, introduced into two Ah pouch cells-based on a LiMnfepo 4 (cathode) and a Li 4 ti 5 o 12 (anode). The pouch cells with trapping sheets experienced only an 8.0 vol% inflation (2.7 mmol CO 2 per gram of polymers) as opposed to the 40 vol% inflation for the reference sample. Moreover, the cells were cycled for 570 cycles at 1 C and 45 °C before reaching 80% of their retention capacity. The continuous quest for an inexpensive, high-energy battery for electrical vehicles (EVs) and energy storage (ES) applications has pushed industrial scientists to develop cells with high energy density by weight and volume. Optimizing the capacity of active materials in electrodes, and stacking increasingly more electrodes into a large format cell has become a valid path to increasing the energy density in battery packs, and minimizing their cost 1-4. On the other hand, safety should not be compromised, which is a real concern for consumers as no one wants to travel on potential "rolling bombs. " The implementation of a cathode with a high capacity and voltage to increase the battery's energy density is in vogue; consequently, manganese (Mn) or cobalt-based (Co) cathode materials have become prevalent in the production of high energy batteries. However, since the cost of Mn is lower than that of Co, reducing Co in cathode materials is a common approach to reduce cell costs 5. However, increasing the Mn content in active materials can cause other problems. The unwanted dissolution of Mn 2+ in the electrolyte (also initiated by water and HF) during cell operations can cause myriad side effects such as deposits on the anode surface and a reaction with the electrolyte where the liquid electrolyte may degrade rapidly during the first few cycles to produce gas. Gas evolution during cycling is one of the major problems associated with (especially) Mn-based cathodes. These gases principally constitute CO 2 , which originates from the decomposition of the liquid electrolyte in the presence of Mn ions 6-8. In the case of LMO, reaction occurs on the surface with Li + and Mn 2+ , and they are leached from the surface, therefore there is more Li ions migrate from the core, consequently electrons hopping from Mn 3+ to Mn 4+. The disproportionate reaction of Mn 3+ generates Mn 2+ /Mn 4+ which diffuses in electrolytes; studies with LMFP are limited. The degradation of the solvents in the presence of a Li 4 Ti 5 O 12 (LTO) anode and initiated by PF ...

High performance LiMnFePO4/Li4Ti5O12full cells by functionalized polymeric additives

“…Moreover, we report of first example of LMFP / LTO cell at 3.0 V having good cycle-life. There are limited articles on LMFP / LTO cells 42,[45][46][47] and only one LTO-based Li-ion battery was commercialized. 48 Hence, this discovery can pave the way for novel research on additive polymers that can interact positively with active materials or electrolytes during the battery operation in an effort to enhance performance.…”

Acid- and Gas-Scavenging Electrolyte Additive Improving the Electrochemical Reversibility of Ni-Rich Cathodes in Li-Ion Batteries

“…21−25 Although the introduction of pouch films coated with epoxide-containing polymers can reduce pouch swelling through the abovementioned CO 2 capture, the practical application of this strategy is hindered by the difficulty of coating such polymers on aluminum foil. 25 Previously, the coating of TiO rich NCA cathodes during initial cycling did not ensure good cycling stability because of the additional Li site loss at the surface due to the interaction between NCM and TiO 2 . 26 Furthermore, although surface coatings have been introduced to mitigate the direct contact of HF and electrodes, the thickness of coating layers and their compatibility with active materials require further optimization to increase battery longevity.…”

“…Compounds with silyl ether moieties have been examined as effective HF scavengers in LiPF 6 -based electrolytes owing to the high affinity of these moieties to F – ions . Trimethylsilyl (TMS) group-containing additives are capable of HF scavenging but suffer from the concomitant formation of the highly volatile trimethylsilyl fluoride (TMS-F, boiling point = 16 °C). − The epoxide moiety was reported to capture CO 2 via cycloaddition and is therefore expected to restrain pouch swelling when coated on the inside of the pouch bag. − Although the introduction of pouch films coated with epoxide-containing polymers can reduce pouch swelling through the abovementioned CO 2 capture, the practical application of this strategy is hindered by the difficulty of coating such polymers on aluminum foil . Previously, the coating of TiO 2 on Ni-rich cathode material particles to mitigate surface phase transitions and crack propagation in Ni-rich NCA cathodes during initial cycling did not ensure good cycling stability because of the additional Li site loss at the surface due to the interaction between NCM and TiO 2 .…”