A New Strategy to Stabilize Capacity and Insight into the Interface Behavior in Electrochemical Reaction of LiNi0.5Mn1.5O4/Graphite System for High-Voltage Lithium-Ion Batteries

High-Voltage Resistant Ionic Liquids for Lithium-Ion Batteries

With the growing demand for high energy and high power density rechargeable lithium-ion batteries, increasing research is focused on improving the output voltage of these batteries. Herein, a series of pyrrolidinium and piperidinium cations with various N-substituents (including cyanomethyl, benzyl, butyl, hexyl, and octyl groups) were synthesized and investigated with respect to their electrochemical stability under high voltages. The influence of substitutions at the N-position of pyrrolidinium and piperidinium cations on their high-voltage resistance was studied by both theoretical and experimental approaches. The voltage resistance was enhanced as the electron-donating ability of the substitutes increased. Furthermore, 1-hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([C₆Py][TFSI]) exhibited the highest decomposition voltage at approximately 5.12 V and showed promising potential in a lithium-ion battery.

Tailoring Low-Temperature Performance of a Lithium-Ion Battery via Rational Designing Interphase on an Anode

Performances of lithium-ion batteries at subambient temperatures are extremely restricted by the resistive interphases originated from electrolyte decomposition, especially on the anode surface. This work reports a novel strategy that an anode interphase of low impedance is constructed by applying an electrolyte additive dimethyl sulfite (DMS). Electrochemical measurements indicate that the as-constructed interphase provides graphite/LiNi_0.5Co_0.2Mn_0.3O₂ pouch cells with excellent low-temperature performance, outperforming the interphase constructed by 1,3,2-dioxathiolane 2,2-dioxide (DTD), a common commercially used electrolyte additive. Spectral characterizations in combination with theoretical calculations demonstrate that the improved performance is attributed to the unique molecular structure of DMS, which presents appropriate reduction activity and constructs the more stable and ionically conductive anode interphase due to the weaker combination of its reduction product with lithium ions than DTD. This rational design of interphases via an additive structure has been proven to be a low cost but rather an effective approach to tailor the performances of lithium-ion batteries.

Ab Initio Modeling of Transition Metal Dissolution from the LiNi0.5Mn1.5O4 Cathode

Irreversible dissolution of transition metals (TMs) from cathode materials in lithium-ion batteries (LIBs) represents a serious challenge for the application of high-energy-density LIBs. Despite substantial improvements achieved by Ni doping of the LiMn₂O₄ spinel, the promising high-voltage LiNi_0.5Mn_1.5O₄ (LNMO) cathode material still suffers from the loss of electro-active materials (Mn and Ni). This process contributes to the formation of solid-electrolyte interfaces and capacity loss severely limiting the battery life cycle. Here, we combine static and ab initio molecular dynamics free energy calculations based on the density functional theory to investigate the mechanism and kinetics of TM dissolution from LNMO into the liquid organic electrolyte. Our calculations help deconvolute the impact of various factors on TM dissolution rates such as the presence of surface protons and oxygen vacancies and the nature of TMs and electrolyte species. The present study also reveals a linear relationship between adsorption strength of the electrolyte species and TM dissolution barriers that should help design electrode/electrolyte interfaces less vulnerable to TM dissolution.

Truncated octahedral LiNi0.5Mn1.5O4 with excellent electrochemical properties for lithium-ion batteries prepared by a graphite assisted calcination method

A high-performance truncated octahedron structured LiNi_0.5Mn_1.5O₄ is synthesized by a graphite assisted calcination method, in which the {111} and {100} crystal plane group are meet the requirements of high ratio and long cycling performance.

Synthesis and Electrochemical Properties of LiNi0.5Mn1.5O4 for Li-Ion Batteries by the Metal-Organic Framework Method

A LiNi_0.5Mn_1.5O₄ cathode material with high surface orientation was prepared via a complexing reaction coupled with the elevated-temperature solid-state method. First, a bimetal-organic framework containing Ni²⁺ and Mn²⁺ ions was synthesized via a self-assembly route using pyromellitic acid (PMA) as a dispersant and complexing agent. This step was followed by calcination with lithium acetate using PMA as a structure-directing agent. The resulting LiNi_0.5Mn_1.5O₄ (M-LNMO) cathode material was investigated using X-ray diffraction, transmission and scanning electron microscopies, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests. For comparison, LiNi_0.5Mn_1.5O₄ samples were prepared by coprecipitation and the solid-phase method under the same conditions. M-LNMO was highly crystalline with low impurity, uniform grain size, and a preferred orientation in the (111) and (110) planes. Owing to these advantages, the M-LNMO cathode material exhibited overwhelmingly high cyclic stability and rate capability and M-LNMO delivered a capacity of 145 mAh g^-1 at a discharge rate of 0.1C and a discharge capacity retention of 86.6% at 5C after 1000 cycles. Even at an extremely high discharge rate (10C), the specific capacity was 112.7 mAh g^-1, and 78.7% of its initial capacity was retained over 500 cycles. The superior electrochemical performance, particularly during a low-rate operation, was conferred by improved crystallinity and the crystal orientation of the particles.