The composite electrode of CoNiS_x and Ti₃C₂T_x MXene was successfully prepared using a one-step hydrothermal method under the in-situ doping of the cobalt element. The effects of in-situ doping of the cobalt element on the micromorphology and electrochemical performance of the electrodes were investigated. After in-situ doping of the cobalt element, NiS with a needle-like structure was converted into a CoNiS_x with petal-like structure. The petal-like CoNiS_x with a rough surface was very dense and evenly wrapped on the surface and interlamination of Ti₃C₂T_x, which helped increase the specific surface area and pore volume of the electrode. Under the identical test conditions, CoNiS_x@Ti₃C₂T_x had a higher specific capacitance and capacitance retention than NiS@Ti₃C₂T_x. This result indicated that the in-situ doping of the cobalt element promoted the electrochemical performance of the electrode. The energy density of the CoNiS_x@Ti₃C₂T_x/nickel foam (NF)//activated carbon (AC)/NF asymmetric supercapacitor device was 59.20 Wh·kg^–1 at a power density of 826.73 W·kg^–1, which was much higher than that of NiS@Ti₃C₂T_x/NF//AC/NF. Three CoNiS_x@Ti₃C₂T_x/NF//AC/NF in series were able to illuminate the light emitting diode lamp for about 10 min, which was higher than the 5 min of three NiS@Ti₃C₂T_x/NF//AC/NF in series under the same condition. The CoNiS_x@Ti₃C₂T_x/NF//AC/NF with high energy density had better application potential in energy storage than the NiS@Ti₃C₂T_x/NF//AC/NF.