Improved Electrochemical Performance and Thermal Stability of Li-excess Li1.18Co0.15Ni0.15Mn0.52O2 Cathode Material by Li3PO4 Surface Coating

Side Reactions/Changes in Lithium-Ion Batteries: Mechanisms and Strategies for Creating Safer and Better Batteries

Lithium-ion batteries (LIBs), in which lithium ions function as charge carriers, are considered the most competitive energy storage devices due to their high energy and power density. However, battery materials, especially with high capacity undergo side reactions and changes that result in capacity decay and safety issues. A deep understanding of the reactions that cause changes in the battery's internal components and the mechanisms of those reactions is needed to build safer and better batteries. This review focuses on the processes of battery failures, with voltage and temperature as the underlying factors. Voltage-induced failures result from anode interfacial reactions, current collector corrosion, cathode interfacial reactions, overcharge, and over-discharge, while temperature-induced failure mechanisms include SEI decomposition, separator damage, and interfacial reactions between electrodes and electrolytes. The review also presents protective strategies for controlling these reactions. As a result, the reader is offered a comprehensive overview of the safety features and failure mechanisms of various LIB components.

Limiting voltage and capacity fade of lithium-rich, low cobalt Li1.2Ni0.13Mn0.54Fe0.1Co0.03O2 by controlling the upper cut-off voltage

A new Li1.2Ni0.13Mn0.54Fe0.1Co0.03O2 material with a higher content of Fe and lower content of Co was designed via a simple sol-gel method. Moreover, the effect of upper cut-off voltage on the structural stability, capacity and voltage retention was studied. The Li1.2Ni0.13Mn0.54Fe0.1Co0.03O2 electrode delivers a discharge capacity of 250 mA h g-1 with good capacity retention and coulombic efficiency at 4.6 V cut-off voltage. Importantly, improved voltage retention of 94% was achieved. Ex situ XRD and Raman proved that the electrodes cycled at 4.8 V cut-off voltage showed huge structural conversion from layered-to-spinel explaining the poor capacity and voltage retention at this cut-off voltage. In addition, ex situ FT-IR demonstrates that the upper cut-off voltage of 4.8 V exhibits a higher intensity of SEI-related peaks than 4.6 V, suggesting that reducing the upper cut-off voltage can inhibit the growth of the SEI layer. In addition, when the Li1.2Ni0.13Mn0.54Fe0.1Co0.03O2 cathode was paired with a synthesized phosphorus-doped TiO2 anode (P-doped TiO2) in a complete battery cell, it exhibits good capacity and cycling stability at 1C rate. The material developed in this study represents a promising approach for designing high-performance Li-rich, low cobalt cathodes for next-generation lithium-ion batteries.

Integrating surface structure via triphenyl phosphate treatment to stabilize Li-rich Mn-based cathode materials

Li-rich Mn-based layered oxides (LLOs) have emerged as one of the most promising cathode materials for the next-generation lithium-ion batteries (LIBs) because of their high energy density, high specific capacity, and environmental friendliness. These materials, however, have drawbacks such as capacity degradation, low initial coulombic efficiency (ICE), voltage decay, and poor rate performance due to irreversible oxygen release and structural deterioration during cycling. Herein, we present a facile method of triphenyl phosphate (TPP) surface treatment to create an integrated surface structure on LLOs that includes oxygen vacancies, Li₃PO₄, and carbon. When used for LIBs, the treated LLOs show an increased initial coulombic efficiency (ICE) of 83.6% and capacity retention of 84.2% at 1C after 200 cycles. It is suggested that the enhanced performance of the treated LLOs can be attributed to the synergetic functions of each component in the integrated surface, such as the oxygen vacancy and Li₃PO₄ being able to inhibit the evolution of oxygen and accelerate the transport of lithium ions, while the carbon layer can restrain undesirable interfacial side reactions and reduce the dissolution of transition metals. Furthermore, electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) prove an enhanced kinetic property of the treated LLOs cathode, and ex-situ X-ray diffractometer shows a suppressed structural transformation of TPP-treated LLOs during the battery reaction. This study provides an effective strategy for constructing an integrated surface structure on LLOs to achieve high-energy cathode materials in LIBs.

Surface coating of a LiNi x Co y Al1-x-y O2 (x > 0.85) cathode with Li3PO4 for applying a water-based hybrid polymer binder during Li-ion battery preparation

To produce water-stable Ni-rich lithium nickel cobalt aluminum oxides (LiNi _x Co _y Al_1-x-y O₂, x > 0.85, NCAs), the formation of trilithium phosphate (Li₃PO₄)-coated layers on the NCA surfaces was attempted through the use of a surface reaction in a mixture of ethanol and water and a post-heat treatment at 350 and 400 °C. Based on the results of X-ray photoelectron spectroscopy (XPS), the coated layers consisted of nickel phosphate (Ni₃(PO₄)₂) and Li₃PO₄. The coated NCA surface could have sufficient water stability to maintain the cathode performance in a water slurry for 1 day. In addition, the coated layers formed on the NCA surfaces did not block Li⁺-ion transfer through the Ni₃(PO₄)₂/Li₃PO₄-coating layers and enhanced the high-rate discharge performance.

Boosting Electrochemical Performance of Lithium-Rich Manganese-Based Cathode Materials through a Dual Modification Strategy with Defect Designing and Interface Engineering

Low Coulombic efficiency, severe capacity fading and voltage attenuation, and poor rate performance are currently great obstacles for the industrial application of lithium-rich manganese-based cathode materials (LRMCs) in lithium-ion batteries (LIBs). Herein, a dual modification strategy combining defect designing with interface engineering is reported to solve the above problems synchronously. Oxygen vacancies, a carbon nitride protective layer, and a fast ion conductor are simultaneously introduced in the LRMCs. It has been found that oxygen vacancies can suppress the release of irreversible oxygen, which is in favor of improving the initial Coulombic efficiency, the carbon nitride protective layer can improve the structural stability and alleviate the attenuation of capacity and voltage, and the fast ion conductor can promote the diffusion rate of Li⁺ and electron conductivity and thus enhance the rate capability. The modified material exhibits significantly enhanced electrochemical performances, including a favorable capacity retention rate of 94.2% over 120 cycles at 1C (1C = 200 mAh g^-1) and excellent rate capabilities of 173.1 and 136.9 mAh g^-1 can be maintained at 5 and 10C after 100 cycles, respectively. Hence, the well-designed dual modification strategy with defect design and interface engineering provides significant exploration for the development and industrialization of LRMCs with high performance.

Optimizing surface residual alkali and enhancing electrochemical performance of LiNi0.8Co0.15Al0.05O2cathode by LiH2PO4

LiNi_0.8Co_0.15Al_0.05O₂(NCA), a promising ternary cathode material of lithium-ion batteries, has widely attracted attention due to its high energy density and excellent cycling performance. However, the presence of residual alkali (LiOH and Li₂CO₃) on the surface will accelerate its reaction with HF from LiPF₆, resulting in structural degradation and reduced safety. In this work, we develop a new coating material, LiH₂PO₄, which can effectively optimize the residual alkali on the surface of NCA to remove H₂O and CO₂and form a coating layer with excellent ion conductivity. Under this strategy, the coated sample NCA@0.02Li₃PO₄(P2-NCA) provides a capacity of 147.8 mAh g^-1at a high rate of 5 C, which is higher than the original sample (126.5 mAh g^-1). Impressively, the cycling stabilities of P2-NCA under 0.5 C significantly improved from 85.2% and 81.9% of pristine-NCA cathode to 96.1% and 90.5% at 25 °C and 55 °C, respectively. These satisfied findings indicate that this surface modification method provides a feasible strategy toward improving the performance and applicability of nickel-rich cathode materials.

Promoting the Reversible Oxygen Redox Reaction of Li-Excess Layered Cathode Materials with Surface Vanadium Cation Doping

Li-excess layered cathode (LLC) materials have a high theoretical specific capacity of 250 mAh g-1 induced by transition metal (cationic) and oxygen (anionic) redox activity. Especially, the oxygen redox reaction related to the activation of the Li2MnO3 domain plays the crucial role of providing a high specific capacity. However, it also induces an irreversible oxygen release and accelerates the layered-to-spinel phase transformation and capacity fading. Here, it is shown that surface doping of vanadium (V5+) cations into LLC material suppresses both the irreversible oxygen release and undesirable phase transformation, resulting in the improvement of capacity retention. The V-doped LLC shows a high discharge capacity of 244.3 ± 0.8 mAh g-1 with 92% retention after 100 cycles, whereas LLC delivers 233.6 ± 1.1 mAh g-1 with 74% retention. Furthermore, the average discharge voltage of V-doped LLC drops by only 0.33 V after 100 cycles, while LLC exhibits 0.43 V of average discharge voltage drop. Experimental and theoretical investigations indicate that doped V-doping increase the transition metal-oxygen (TM-O) covalency and affect the oxidation state of peroxo-like (O2) n - species during the delithiation process. The role of V-doping to make the oxygen redox reversible in LLC materials for high-energy density Li-ion batteries is illustrated here.

Surface Modification of LiNi0.8 Co0.15 Al0.05 O2 Particles via Li3 PO4 Coating to Enable Aqueous Electrode Processing

The successful implementation of an aqueous-based electrode manufacturing process for nickel-rich cathode active materials is challenging due to their high water sensitivity. In this work, the surface of LiNi0.8 Co0.15 Al0.05 O2 (NCA) was modified with a lithium phosphate coating to investigate its ability to protect the active material during electrode production. The results illustrate that the coating amount is crucial and a compromise has to be made between protection during electrode processing and sufficient electronic conductivity through the particle surface. Cells with water-based electrodes containing NCA with an optimized amount of lithium phosphate had a slightly lower specific discharge capacity than cells with conventional N-methyl-2-pyrrolidone-based electrodes. Nonetheless, the cells with optimized water-based electrodes could compete in terms of cycle life.

Passivation of the Cathode-Electrolyte Interface for 5 V-Class All-Solid-State Batteries

An all-solid-state battery is a potentially superior alternative to a state-of-the-art lithium-ion battery owing to its merits in abuse tolerance, packaging, energy density, and operable temperature ranges. In this work, a 5 V-class spinel LiNi_0.5Mn_1.5O₄ (LNMO) cathode is targeted to combine with a high-ionic-conductivity Li₆PS₅Cl (LPSCl) solid electrolyte for developing high-performance all-solid-state batteries. Aiming to passivate and stabilize the LNMO-LPSCl interface and suppress the unfavorable side reactions such as the continuous chemical/electrochemical decomposition of the solid electrolyte, oxide materials including LiNbO₃, Li₃PO₄, and Li₄Ti₅O₁₂ are rationally applied to decorate the surface of pristine LNMO particles with various amounts through a wet-chemistry approach. Electrochemical characterization demonstrates that the composite cathode consisting of 8 wt % LiNbO₃-coated LNMO and LPSCl in a weight ratio of 70:30 delivers the best electrochemical performance with an initial discharge capacity of 115 mA h g^-1 and a reversible discharge capacity of 80 mA h g^-1 at the 20th cycle, suggesting that interfacial passivation is an effective strategy to ensure the operation of 5 V-class all-solid-state batteries.

Li3PO4 modification on a primary particle surface for high performance Li-rich layered oxide Li1.18Mn0.52Co0.15Ni0.15O2via a synchronous route

A Li-rich layered oxide, Li_1.18Mn_0.52Co_0.15Ni_0.15O₂, with Li₃PO₄ modification on the surface of a primary particle, was synthesized by a facile synchronous method.

Understanding the Effect of Atomic-Scale Surface Migration of Bridging Ions in Binding Li3PO4 to the Surface of Spinel Cathode Materials

Spinel cathode materials (e.g., LiMn₂O₄ and LiNi_0.5Mn_1.5O₄) with strongly bonded surface coatings are desirable for delivering improved electrochemical performance in long-term cycling. Here, we report that the introduction of bridging ions such as Fe and Co, which can diffuse into both the spinel cathode materials and Li₃PO₄, the latter is found to cover the spinel surface in the form of dense and uniform particles (∼2-3 nm). Detailed structural analysis of the surface reveals that the bridging ions diffuse into the 16c site of the spinel structure to form ion-doped spinel cathode materials, which contribute to the formation of strong bonds between the surface and Li₃PO₄, possibly via spinel-(surface bridging ions)-Li₃PO₄ bonds. The critical role of the surface bridging ions is further investigated by heating the as-formed Li₃PO₄-coated spinel cathode materials (with bridging ions) to high temperatures, resulting in further diffusion of bringing ions from the surface to the interior of the spinel materials and consequently depletion of the surface spinel-(surface bridging ions)-Li₃PO₄ bonds. This leads to the gradual growth of surface Li₃PO₄ particles (∼20 nm) and the exposure of the spinel surface.

Ni-Rich LiNi0.8Co0.1Mn0.1O2 Oxide Coated by Dual-Conductive Layers as High Performance Cathode Material for Lithium-Ion Batteries

Ni-rich materials are appealing to replace LiCoO₂ as cathodes in Li-ion batteries due to their low cost and high capacity. However, there are also some disadvantages for Ni-rich cathode materials such as poor cycling and rate performance, especially under high voltage. Here, we demonstrate the effect of dual-conductive layers composed of Li₃PO₄ and PPy for layered Ni-rich cathode material. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy show that the coating layers are composed of Li₃PO₄ and PPy. (NH₄)₂HPO₄ transformed to Li₃PO₄ after reacting with surface lithium residuals and formed an inhomogeneous coating layer which would remarkably improve the ionic conductivity of the cathode materials and reduce the generation of HF. The PPy layer could form a uniform film which can make up for the Li₃PO₄ coating defects and enhance the electronic conductivity. The stretchy PPy capsule shell can reduce the generation of internal cracks by resisting the internal pressure as well. Thus, ionic and electronic conductivity, as well as surface structure stability have been enhanced after the modification. The electrochemistry tests show that the modified cathodes exhibited much improved cycling stability and rate capability. The capacity retention of the modified cathode material is 95.1% at 0.1 C after 50 cycles, whereas the bare sample is only 86%, and performs 159.7 mAh/g at 10 C compared with 125.7 mAh/g for the bare. This effective design strategy can be utilized to enhance the cycle stability and rate performance of other layered cathode materials.