MXene-bonded flexible hard carbon film as anode for stable Na/K-ion storage ---Advanced Functional Materials, 2019, 29, 1906282.

Ning Sun, Qizhen Zhu, Babak Anasori, Peng Zhang, Huan Liu, Yury Gogotsi,* and Bin Xu*

      Hard carbon (HC) is a promising anode material for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs), but the volume change during the insertion/extraction of Na⁺ or K⁺ limits the cycle life, especially for PIBs due to the large ion size of K⁺. Moreover, the conventional anodes fabricated through the coating method cannot satisfy the requirement of flexible devices. Here, it is shown that 2D carbide flakes of Ti₃C₂T_x MXene can be used as multifunctional conductive binders for flexible HC electrodes. The use of MXene nanosheets eliminates the need for all the electrochemically inactive components in the conventional polyvinylidene fluoride–bonded HC electrode, including polymer binders, conductive additives, and current collectors. In MXene-bonded HC electrodes, conductive and hydrophilic MXene 2D nanosheets construct a 3D network, which can effectively stabilize the electrode structure and accommodate the volume expansion of HC during the charge/discharge process, leading to an enhanced electrode capacity and excellent cycle performance as anodes for both SIBs and PIBs. Benefiting from the 3D conductive network, the MXene-bonded HC film electrodes also present improved rate capability, indicating MXene is a very promising multifunctional binder for next-generation flexible secondary rechargeable batteries.