Enhanced Electrochemical Performance of LiNi(0.5)Mn(1.5)O(4) Composite Cathodes for Lithium-Ion Batteries by Selective Doping of K(+)/Cl(−) and K(+)/F(−)

K(+)/Cl(−) and K(+)/F(−) co-doped LiNi(0.5)Mn(1.5)O(4) (LNMO) materials were successfully synthesized via a solid-state method. Structural characterization revealed that both K(+)/Cl(−) and K(+)/F(−) co-doping reduced the Li(x)Ni(1)(−)(x)O impurities and enlarged the lattice parameters compared to those of pure LNMO. Besides this, the K(+)/F(−) co-doping decreased the Mn(3+) ion content, which could inhibit the Jahn–Teller distortion and was beneficial to the cycling performance. Furthermore, both the K(+)/Cl(−) and the K(+)/F(−) co-doping reduced the particle size and made the particles more uniform. The K(+)/Cl(−) co-doped particles possessed a similar octahedral structure to that of pure LNMO. In contrast, as the K(+)/F(−) co-doping amount increased, the crystal structure became a truncated octahedral shape. The Li(+) diffusion coefficient calculated from the CV tests showed that both K(+)/Cl(−) and K(+)/F(−) co-doping facilitated Li(+) diffusion in the LNMO. The impedance tests showed that the charge transfer resistances were reduced by the co-doping. These results indicated that both the K(+)/Cl(−) and the K(+)/F(−) co-doping stabilized the crystal structures, facilitated Li(+) diffusion, modified the particle morphologies, and increased the electrochemical kinetics. Benefiting from the unique advantages of the co-doping, the K(+)/Cl(−) and K(+)/F(−) co-doped samples exhibited improved rate and cycling performances. The K(+)/Cl(−) co-doped Li(0.97)K(0.03)Ni(0.5)Mn(1.5)O(3.97)Cl(0.03) (LNMO-KCl0.03) exhibited the best rate capability with discharge capacities of 116.1, 109.3, and 93.9 mAh g(−1) at high C-rates of 5C, 7C, and 10C, respectively. Moreover, the K(+)/F(−) co-doped Li(0.98)K(0.02)Ni(0.5)Mn(1.5)O(3.98)F(0.02) (LNMO-KF0.02) delivered excellent cycling stability, maintaining 85.8% of its initial discharge capacity after circulation for 500 cycles at 5C. Therefore, the K(+)/Cl(−) or K(+)/F(−) co-doping strategy proposed herein will play a significant role in the further construction of other high-voltage cathodes for high-energy LIBs.