High‐Performance Silicon Anodes Enabled By Nonflammable Localized High‐Concentration Electrolytes

Abstract

electric vehicles. [1] LIBs with the conventional carbonaceous anode materials such as graphite have played a dominant role in the current market of customer electronics and electrical transportation. However, low capacity of carbonaceous anode materials (372 mAh g −1 ) also limits the further increase in energy densities of LIBs. [2] In this regard, silicon (Si)-based anode is considered as one of the most promising anode candidates in further boosting the specific energy of LIBs because Si has one of the highest practical capacity of 3579 mAh g −1 among various anode materials and a relatively low lithiation potential of 0.2 V versus Li/Li + . However, fast capacity fade and large swelling of Si anodes related to their large volume expansion (>300%) upon lithiation greatly hindered their deployment in practical applications. [3] There has been significant progress toward understanding and mitigating the capacity fade in Si-based anodes, including exploiting nanostructured Si materials, [4] porous structures, [5] surface coatings, [6] core-shell structures, [7] and novel binders. [8] However, the development of novel electrolytes for Si-based anodes is relatively slow because most researches have been focused on the structure development of Si electrodes. The conventional electrolytes for Si anodes are LiPF 6 /carbonate-based electrolytes with a certain amount of fluoroethylene carbonate (FEC) as an additive or cosolvent (from 5% to 10% by weight in the electrolytes). [9] Linear carbonate solvents usually have relatively low flashpoints, so they are easily ignited and may lead to safety problems under certain extreme conditions. [10] In addition, the formed solid electrolyte interphase (SEI) on anode surface in conventional carbonate electrolytes is unstable and cannot withstand the large volume changes of Si during cycling. Although the introduction of FEC in the conventional LiPF 6 / carbonate electrolytes can improve the cycling performance of Si anodes, increased amount of FEC may lead to increased gassing in full cells. Because such high content of FEC in the electrolytes may form a detrimental cathode electrolyte interface (CEI) on cathode surface and generate a serious gassing issue especially at high charge cutoff voltages and elevated temperatures, which lead to impedance increase, capacity fading and safety issue of the Si-based full cells. Therefore, the Silicon anodes are regarded as one of the most promising alternatives to graphite for high energy-density lithium-ion batteries (LIBs), but their practical applications have been hindered by high volume change, limited cycle life, and safety concerns. In this work, nonflammable localized highconcentration electrolytes (LHCEs) are developed for Si-based anodes. The LHCEs enable the Si anodes with significantly enhanced electrochemical performances comparing to conventional carbonate electrolytes with a high content of fluoroethylene carbonate (FEC). The LHCE with only 1.2 wt% FEC can further improve the long-term cycling stability of Si-base...

Role of inner solvation sheath within salt–solvent complexes in tailoring electrode/electrolyte interphases for lithium metal batteries

“…As a result, cation-anion and ion-solvent interactions in the inner solvation sheath of LHCE are further enhanced. This phenomenon has been evidenced by different experimental observations lately: the further deviation from the "ideal" KCl line in Walden plots (indicating fully dissociated ions) and the distinctive chemical shifts of coordinating oxygen atoms from 17 O-NMR spectra, compared to those in parallel HCEs (24,27,28). Therefore, the LHCE system can serve as a unique platform for investigating the properties of the inner solvation sheath and its role in the interfacial reaction processes between electrodes and electrolytes.…”

The Latest Trends in Electric Vehicles Batteries

“…Adding elements to binders that affect side reactions between anode and electrolyte is only one possible solution for improving the kinetics of SEI formation and growth. Jia et al [ 120 ] highlighted the detrimental effect carbonates contained in electrolytes, most commonly fluoroethylene carbonate, have in terms of SEI stability, and risk of flammability. The authors fabricated an electrolyte with higher salt concentration, a technique well established for Li-metal anodes, based on a similarity between stability issues in Si and Li-metal anodes.…”

“…( c ) Charge/discharge curves, and rate capability of half-cells with Si anode and high salt concentration liquid electrolyte. Reproduced with permission [ 120 ].…”

Morphology engineering of silicon nanoparticles for better performance in Li-ion battery anodes

“…7 Several approaches have been proposed to overcome the failure mechanisms outlined above not only from the perspective of materials development but also through optimization of other components. 8 The preparation of porous Si or even Si hollow nanospheres has been suggested to counteract the expansion/contraction process. [9][10][11][12][13] Nanostructuring could also be applied to Si to produce nanowires or thin Si layers which have been shown to have better stability compared to the bulk.…”