2-thiophene sulfonamide (2-TS) is demonstrated as a multi-functional additive to functionalize the electrolyte and improve the performances of LiNi_0.8Mn_0.1Co_0.1O₂ (NCM811)/graphite batteries. Compared with the batteries without 2-TS, the performances of batteries with 2-TS containing electrolyte are significantly improved at wide temperature and high cut-off charge voltage of 4.40 V (vs. Li/Li⁺）. After 500 cycles at room temperature and in the voltage range of 2.80–4.20 V, the batteries with 1% 2-TS and without 2-TS additive lose 8.40% and 23.59% initial discharge capacity, respectively. At an elevated temperature of 45 °C and in the voltage range of 2.80–4.40 V, the cycle performance of the batteries with 1% 2-TS is also enhanced, i.e., 68.68% initial discharge capacity is remained after 115 cycles, while the batteries without 2-TS has already decayed to the lifespan point. It is shown that 2-TS molecules can both consume the H₂O/HF residues to alleviate the decomposition of LiPF₆ and preferentially react on the electrodes to form uniform and dense low-resistance films. These results demonstrate this electrolyte can effectively improve the battery performances and has promising prospects applying in high-voltage and high-nickel NCM-based batteries.