An electrolyte additive for the improved high voltage performance of LiNi0.5Mn1.5O4 (LNMO) cathodes in Li-ion batteries

Li-Site Defects Induce Formation of Li-Rich Impurity Phases: Implications for Charge Distribution and Performance of LiNi0.5- xMxMn1.5O4 Cathodes (M = Fe and Mg; x = 0.05-0.2)

An understanding of the structural properties that allow for optimal cathode performance, and their origin, is necessary for devising advanced cathode design strategies and accelerating the commercialization of next-generation cathodes. High-voltage, Fe- and Mg-substituted LiNi0.5Mn1.5O4 cathodes offer a low-cost, cobalt-free, yet energy-dense alternative to commercial cathodes. In this work, the effect of substitution on several important structure properties is explored, including Ni/Mn ordering, charge distribution, and extrinsic defects. In the cation-disordered samples studied, a correlation is observed between increased Fe/Mg substitution, Li-site defects, and Li-rich impurity phase formation-the concentrations of which are greater for Mg-substituted samples. This is attributed to the lower formation energy of MgLi defects when compared to FeLi defects. Li-site defect-induced impurity phases consequently alter the charge distribution of the system, resulting in increased [Mn3+] with Fe/Mg substitution. In addition to impurity phases, other charge compensators are also investigated to explain the origin of Mn3+ (extrinsic defects, [Ni3+], oxygen vacancies and intrinsic off-stoichiometry), although their effects are found to be negligible.

Subtractive transformation of cathode materials in spent Li-ion batteries to a low-cobalt 5 V-class cathode material

Adding extra raw materials for direct recycling or upcycling is prospective for battery recycling, but overlooks subtracting specific components beforehand can facilitate the recycling to a self-sufficient mode of sustainable production. Here, a subtractive transformation strategy of degraded LiNi0.5Co0.2Mn0.3O2 and LiMn2O4 to a 5 V-class disordered spinel LiNi0.5Mn1.5O4-like cathode material is proposed. Equal amounts of Co and Ni from degraded materials are selectively extracted, and the remaining transition metals are directly converted into Ni0.4Co0.1Mn1.5(CO3)2 precursor for preparing cathode material with in-situ Co doping. The cathode material with improved conductivity and bond strength delivers high-rate (10 C and 20 C) and high-temperature (60 °C) cycling stability. This strategy with no extra precursor input can be generalized to practical degraded black mass and reduces the dependence of current cathode production on rare elements, showing the potential of upcycling from the spent to a next-generation 5 V-class cathode material for the sustainable Li-ion battery industry.

Additive Strategy Enhancing In Situ Polymerization Uniformity for High-Voltage Sodium Metal Batteries

In situ polymerization to prepare quasi-solid electrolyte has attracted wide attentions for its advantage in achieving intimate electrode-electrolyte contact and the high process compatibility with current liquid batteries; however, gases can be generated during polymerization process and remained in the final electrolyte, severely impairing the electrolyte uniformity and electrochemical performance. In this work, an in situ polymerized poly(vinylene carbonate)-based quasi-solid electrolyte for high-voltage sodium metal batteries (SMBs) is demonstrated, which contains a novel multifunctional additive N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA). MSTFA as high-efficient plasticizer diminishes residual gases in electrolyte after polymerization; the softer and homogeneous electrolyte enables much faster ionic conduction. The HF/H2 O scavenge effect of MSTFA mitigates the corrosion of free acid to cathode and interfacial passivating layers, enhancing the cycle stability under high voltage. As a result, the 4.4 V Na||Na3 V2 (PO4 )2 F3 cell employing the optimized electrolyte possesses an initial discharge capacity of 112.0 mAh g-1 and a capacity retention of 91.3% after 100 cycles at 0.5C, obviously better than those of its counterparts without MSTFA addition. This work gives a pioneering study on the gas residue phenomenon in in situ polymerized electrolytes, and introduces a novel multifunctional silane additive that effectively enhances electrochemical performance in high-voltage SMBs, showing practical application significance.