Abstract
Lithium–sulfur (Li–S) batteries have a high specific capacity, but lithium polysulfide (LPS) diffusion and lithium dendrite growth drastically reduce their cycle life. High discharge rates also necessitate their resilience to high temperature. Here we show that biomimetic self-assembled membranes from aramid nanofibers (ANFs) address these challenges. Replicating the fibrous structure of cartilage, multifactorial engineering of ion-selective mechanical, and thermal properties becomes possible. LPS adsorption on ANF surface creates a layer of negative charge on nanoscale pores blocking LPS transport. The batteries using cartilage-like bioinspired ANF membranes exhibited a close-to-theoretical-maximum capacity of 1268 mAh g−1, up to 3500+ cycle life, and up to 3C discharge rates. Essential for safety, the high thermal resilience of ANFs enables operation at temperatures up to 80 °C. The simplicity of synthesis and recyclability of ANFs open the door for engineering high-performance materials for numerous energy technologies.
Highlights
Lithium–sulfur (Li–S) batteries have a high specific capacity, but lithium polysulfide (LPS) diffusion and lithium dendrite growth drastically reduce their cycle life
Thermogravimetric analysis (TGA) on np-aramid nanofibers (ANFs) membrane indicates that no significant weight loss occurs below 600 °C in N2 atmosphere (Fig. 1D), and the differential scanning calorimetry (DSC) analysis on np-ANF confirms no significant change occurring with np-ANF until 500 °C (Supplementary Figs. 2, 3). np-ANF membranes show lower electrolyte contact angle and higher electrolyte uptake compared to CelgardTM 2400, which reduces internal resistance needed to achieve superior rate charge−discharge rate (Supplementary Fig. 4)
The highly interconnected cartilage-like pectolated network of nanofibers engenders small volume changes of np-ANF after being fully wetted by electrolyte, which facilitates tight adhesion to electrodes and is needed for efficient dendrite suppression that may not be the case for many other membrane architectures (Supplementary Fig. 5). np-ANF membranes obtained by spincoating with poly(diallyldimethylammonium chloride) (PDDA) features nanoscale pores 0.9–1.2 nm in diameter as determined by the Barrett-Joyner-Halenda (BJH) analysis (Supplementary Fig. 6), which is smaller than the hydrodynamic diameter of L2S4 of 1.3–1.5 nm[2,46,47]
Summary
Lithium–sulfur (Li–S) batteries have a high specific capacity, but lithium polysulfide (LPS) diffusion and lithium dendrite growth drastically reduce their cycle life. The problem of the LPS diffusion can be approached by optimizing the materials design of ion-conducting membranes that can block the LPS transport from S cathode to Li anode. The great challenge for all of these materials solutions for LPS membranes is to combine at least two contrarian materials properties—efficient ion transport and mechanical robustness in one material or a coating[5,15,26] Among the latter, polymers with high shear modulus are necessary to suppress dendrite growth on lithium anodes[27] while high mechanical strength (>98 MPa) and thermal stability
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