HEPES-Assisted Co-Precipitation Synthesis of LiNi_0.5Mn_1.5O₄: Tuning the Mn³⁺ Content and Electrochemical Properties by pH Values

Abstract

Spinel LiNi0.5Mn1.5O4 material (LNMO) is now actively developed as a promising cathode for next generation lithium-ion batteries due to its high specific energy, high rate capability, high operating potential, and low cost. However, its performance degradation originating from transition metal dissolution and severe side reactions remains a critical challenge. Herein, a new solution system 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES) buffer solution for the synthesis of the spinel LiNi0.5Mn1.5O4 material is reported, which is not only the pH stabilizer, but also the chelating agent. The obtained LNMO exhibits excellent electrochemical performance, and its capacity retention is kept as 95.8%, and 88.9% after cycled at 5 C and 10 C for 1000 times, respectively. These can be attributed to homogenous distributions of elements in the as-prepared carbonate precursors, stable pH value of reaction base solution and suitable Mn3+ content in pure LNMO.

Synthesis of high-voltage cathode material using the Taylor-Couette flow-based co-precipitation method

“…The BET specific surface areas of the C-LNMO and TC-LNMO samples were 0.58 and 2.61 m 2 g −1 , respectively. A high specific surface area can result in a high contact area between the electrode and electrolyte, resulting in rapid diffusion of Li + ions ( Wu et al, 2021 ). Therefore, these characteristics are expected to improve the electrochemical performance of TC-LNMO cathode material.…”

“…The equivalent circuit corresponding to the EIS spectra is shown in Figure 8C , where R ohm is the ohm resistance corresponding to the intercept of the semicircle in the high-frequency range, and R s is the resistance of the surface, which corresponds to the semicircle in the high-frequency range. R ct is the charge transfer resistance corresponding to the semicircle of the medium-frequency region, and the inclined line in the low-frequency region represents the Warburg impedance (W) ( Li et al, 2020b ; Wu et al, 2021 ). The resistance values of the C-LNMO and TC-LNMO samples are listed in Table 2 .…”

Doping and Coating Synergy to Improve the Rate Capability and Cycling Stability of Lithium-Rich Cathode Materials for Lithium-Ion Batteries

“…The target product Li 1.2 Mn 0.54 Co 0.13 Ni 0.13 O 2 material was synthesized by a method of co-precipitation in N -(2-hydroxyethyl)­piperazine- N ′-ethanesulfonic acid (HEPES) buffer solution followed by high-temperature calcination (Figure S1a). HEPES buffer solution (pH = 7.8) was prepared according to the literature. , The pH value was measured using a DELTA 320 pH meter (Mettler-Toledo Instruments, USA). In a typical process, the HEPES buffer solution (200 mmol L –1 , pH = 7.5) was fed into a three-necked flask as the basic solution.…”

“…HEPES buffer solution (pH = 7.8) was prepared according to the literature. 5,37 The pH value was measured using a DELTA 320 pH meter (Mettler-Toledo Instruments, USA). In a typical process, the HEPES buffer solution (200 mmol L −1 , pH = 7.5) was fed into a three-necked flask as the basic solution.…”