Study of Immersion of LiNi0.5Mn0.3Co0.2O2 Material in Water for Aqueous Processing of Positive Electrode for Li-Ion Batteries

Gas Evolution Kinetics in Overlithiated Positive Electrodes and its Impact on Electrode Design

Increasing lithium contents within the lattice of positive electrode materials is projected in pursuit of high-energy-density batteries. However, it intensifies the release of lattice oxygen and subsequent gas evolution during operations. This poses significant challenges for managing internal pressure of batteries, particularly in terms of the management of gas evolution in composite electrodes-an area that remains largely unexplored. Conventional assumptions postulate that the total gas evolution is estimated by multiplying the total particle count by the quantities of gas products from an individual particle. Contrarily, this investigation on overlithiated materials-a system known to release the lattice oxygen-demonstrates that loading densities and inter-particle spacing in electrodes significantly govern gas evolution rates, leading to distinct extents of gas formation despite of an equivalent quantity of released lattice oxygen. Remarkably, this study discoveres that O2 and CO2 evolution rates are proportional to 1O2 concentration by the factor of second and first-order, respectively. This indicates an exceptionally greater change in the evolution rate of O2 compared to CO2 depending on local 1O2 concentration. These insights pave new routes for more sophisticated approaches to manage gas evolution within high-energy-density batteries.

To Enhance the Performance of LiNi0.5Co0.2Mn0.3O2 Aqueous Electrodes by the Coating Process

The Li+/H+ cation exchange reactions occur when the cathode is exposed to water and can cause the degradation of battery performance, posing a significant challenge in the preparation of cathode aqueous electrodes. In this study, kh570 [3-(trimethoxysilyl)propyl methacrylate] is used to coat and modify the surface of LiNi0.5Co0.2Mn0.3O2 cathode particles. During the coating process, kh570 undergoes hydrolysis to generate silanol groups, which are subsequently bonded onto the surface of cathode particles and undergo self-polymerization through condensation reactions. As a result, a coating layer forms on the surface of the cathode. This change alters the surface properties of the cathode particles from hydrophilic to hydrophobic, thereby increasing their resistance to water. The coating layers reduce direct contact with water and minimizes internal particle microcracks formation in aqueous electrode processing. After the preparation of aqueous electrodes, the modified cathode exhibits lower transfer resistance and lower polarization, improving both the current rate performance and the cycling performance of the battery.

Important Impact of the Slurry Mixing Speed on Water-Processed Li4Ti5O12 Lithium-Ion Anodes in the Presence of H3PO4 as the Processing Additive

The aqueous processing of lithium transition metal oxides into battery electrodes is attracting a lot of attention as it would allow for avoiding the use of harmful N-methyl-2-pyrrolidone (NMP) from the cell fabrication process and, thus, render it more sustainable. The addition of slurry additives, for instance phosphoric acid (PA), has been proven to be highly effective for overcoming the corresponding challenges such as aluminum current collector corrosion and stabilization of the active material particle. Herein, a comprehensive investigation of the effect of the ball-milling speed on the effectiveness of PA as a slurry additive is reported using Li₄Ti₅O₁₂ (LTO) as an exemplary lithium transition metal oxide. Interestingly, at elevated ball-milling speeds, rod-shaped lithium phosphate particles are formed, which remain absent at lower ball-milling speeds. A detailed surface characterization by means of SEM, EDX, HRTEM, STEM-EDX, XPS, and EIS revealed that in the latter case, a thin protective phosphate layer is formed on the LTO particles, leading to an improved electrochemical performance. As a result, the corresponding lithium-ion cells comprising LTO anodes and LiNi_0.5Mn_0.3Co_0.2O₂ (NMC₅₃₂) cathodes reveal greater long-term cycling stability and higher capacity retention after more than 800 cycles. This superior performance originates from the less resistive electrode-electrolyte interphase evolving upon cycling, owing to the interface-stabilizing effect of the lithium phosphate coating formed during electrode preparation. The results highlight the importance of commonly neglected─frequently not even reported─electrode preparation parameters.

Interfacial Reviving of the Degraded LiNi0.8 Co0.1 Mn0.1 O2 Cathode by LiPO3 Repair Strategy

Nickel-rich cathode materials, owing to their high energy density and low cost, are considered to be one of the cathodes with the most potential in next-generation lithium-ion batteries. Unfortunately, this kind of cathode with highly active surface is easy to react with H₂ O and CO₂ when exposed to ambient air, resulting in the formation of lithium impurities and interfacial phase transition as well as deterioration of the electrochemical properties. In this work, the evolution mechanism of the structure and interface of LiNi_0.8 Co_0.1 Mn_0.1 O₂ during air-exposure is systematically investigated. Furthermore, a facile reviving strategy is proposed to restore the degraded LiNi_0.8 Co_0.1 Mn_0.1 O₂ by using LiPO₃ as the repair agent. The lithium impurities on the surface of the degraded sample can transform into the repair/coating layer, and part of the rock salt phase on the subsurface can revive to layered phase after repair heat treatment. As a result, the optimized cathode delivers an initial discharge capacity of 198.3 mAh g^-1 at 0.1C and a capacity retention of 85.5% after 50 cycles. Although slightly lower than the bare sample (201 mAh g^-1 and 88%), they are obviously higher than the exposed samples (166.5 mAh g^-1 and 40.4%). The regenerated electrochemical properties should be attributed to the multifunctional repair layer that can efficiently reduce the surface lithium impurities, prevent the corrosion of electrolyte, and improve the interfacial Li⁺ diffusion kinetics. This work can effectively reduce the waste of the degraded Ni-rich ternary materials and realize the transformation of "waste" into wealth.

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.

Characterization and Laser Structuring of Aqueous Processed Li(Ni0.6Mn0.2Co0.2)O2 Thick-Film Cathodes for Lithium-Ion Batteries

Lithium-ion batteries have led the revolution in portable electronic devices and electrical vehicles due to their high gravimetric energy density. In particular, layered cathode material Li(Ni_0.6Mn_0.2Co_0.2)O₂ (NMC 622) can deliver high specific capacities of about 180 mAh/g. However, traditional cathode manufacturing involves high processing costs and environmental issues due to the use of organic binder polyvinylidenfluoride (PVDF) and highly toxic solvent N-methyl-pyrrolidone (NMP). In order to overcome these drawbacks, aqueous processing of thick-film NMC 622 cathodes was studied using carboxymethyl cellulose and fluorine acrylic hybrid latex as binders. Acetic acid was added during the mixing process to obtain slurries with pH values varying from 7.4 to 12.1. The electrode films could be produced with high homogeneity using slurries with pH values smaller than 10. Cyclic voltammetry measurements showed that the addition of acetic acid did not affect the redox reaction of active material during charging and discharging. Rate capability tests revealed that the specific capacities with higher slurry pH values were increased at C-rates above C/5. Cells with laser structured thick-film electrodes showed an increase in capacity by 40 mAh/g in comparison to cells with unstructured electrodes.

High Power Cathodes from Poly(2,2,6,6-Tetramethyl-1-Piperidinyloxy Methacrylate)/Li(NixMnyCoz)O2 Hybrid Composites

Lithium-ion batteries are today among the most efficient devices for electrochemical energy storage. However, an improvement of their performance is required to address the challenges of modern grid management, portable technology, and electric mobility. One of the most important limitations to solve is the slow kinetics of redox reactions associated to inorganic cathodic materials, directly impacting on the charging time and the power characteristics of the cells. In sharp contrast, redox polymers such as poly(2,2,6,6-tetramethyl-1-piperidinyloxy methacrylate) (PTMA) exhibit fast redox reaction kinetics and pseudocapacitors characteristics. In this contribution, we have hybridized high energy Li(Ni_xMn_yCo_z)O₂ mixed oxides (NMC) with PTMA. In this hybrid cathode configuration, the higher voltage NMC (ca. 3.7 V vs. Li/Li⁺) is able to transfer its energy to the lower voltage PTMA (3.6 V vs. Li/Li⁺) improving the discharge power performances and allowing high power cathodes to be obtained. However, the NMC-PTMA hybrid cathodes show an important capacity fading. Our investigations indicate the presence of an interface degradation reaction between NMC and PTMA transforming NMC into an electrochemically dead material. Moreover, the aqueous process used here to prepare the cathode is also shown to enable the degradation of NMC. Indeed, once NMC is immersed in water, alkaline surface species dissolve, increasing the pH of the slurry, and corroding the aluminum current collector. Additionally, the NMC surface is altered due to delithiation which enables the interface degradation reaction to take place. This reaction by surface passivation of NMC particles did not succeed in preventing the interfacial degradation. Degradation was, however, notably decreased when Li(Ni_0.8Mn_0.1Co_0.1)O₂ NMC was used and even further when alumina-coated Li(Ni_0.8Mn_0.1Co_0.1)O₂ NMC was considered. For the latter at a 20C discharge rate, the hybrids presented higher power performances compared to the single constituents, clearly emphasizing the benefits of the hybrid cathode concept.

Current and future lithium-ion battery manufacturing

Lithium-ion batteries (LIBs) have become one of the main energy storage solutions in modern society. The application fields and market share of LIBs have increased rapidly and continue to show a steady rising trend. The research on LIB materials has scored tremendous achievements. Many innovative materials have been adopted and commercialized by the industry. However, the research on LIB manufacturing falls behind. Many battery researchers may not know exactly how LIBs are being manufactured and how different steps impact the cost, energy consumption, and throughput, which prevents innovations in battery manufacturing. Here in this perspective paper, we introduce state-of-the-art manufacturing technology and analyze the cost, throughput, and energy consumption based on the production processes. We then review the research progress focusing on the high-cost, energy, and time-demand steps of LIB manufacturing. Finally, we share our views of challenges in LIB manufacturing and propose future development directions for manufacturing research in LIBs.

Effects of Extended Aqueous Processing on Structure, Chemistry, and Performance of Polycrystalline LiNixMnyCozO2 Cathode Powders

The prospect of aqueous processing of LiNi_xMn_yCo_zO₂ (NMC) cathodes has significant appeal to battery manufacturers for the reduction in materials cost, toxicological risk, and environmental impact compared to conventional N-methyl-2-pyrrolidone (NMP)-based processing. However, the effects of aqueous processing of NMC powders at industrial timescales are not well studied, with prior studies mostly focusing on relatively brief water washing processes. In this work, we investigate the bulk and surface impacts of extended aqueous processing of polycrystalline NMC powders with different compositions. We demonstrate that at timescales of several hours, polycrystalline NMC is susceptible to intergranular fracture, with the severity of fracture scaling with the NMC nickel content. While bulk crystallinity and composition are unchanged, surface sensitive techniques such as X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) indicate that the exposure of water leads to a level of delithiation, nickel reduction, and reconstruction from the layered to rock-salt structure at the surface of individual grains. Dynamic single NMC microparticle compression testing suggests that the resulting mechanical stresses weaken the integrity of the polycrystalline particle and increases susceptibility of intergranular fracture. The initially degraded surfaces along with the increased surface area lead to faster capacity fade and impedance growth during electrochemical cycling. From this work, it is demonstrated that NMC powders require surface or grain boundary modifications to make industrial-scale aqueous cathode processing viable, especially for next-generation nickel-rich NMC chemistries.

Clean the Ni-Rich Cathode Material Surface With Boric Acid to Improve Its Storage Performance

The existence of residual lithium compounds (RLCs) on the surface of layered Ni-rich materials will deteriorate the electrochemical properties and cause safety problem. This work presents an effective surface washing method to remove the RLCs from LiNi_0.90Co_0.06Mn_0.04O₂ material surface, via ethyl alcohol solution that contains low concentration of boric acid. It is a low-cost process because the filter liquor can be recycled. The optimal parameters including washing time, boric acid concentration, and solid-liquid ratio were systematically studied. It has been determined by powder pH and Fourier transform infrared spectra results that the amount of RLCs was reduced effectively, and the storage performance was significantly enhanced for the washed samples. The 150th capacity retentions after storing had increased from 68.39% of pristine material to 85.46-94.84% of the washed materials. The performance enhancements should be ascribed to the surface washing process, which removed not only the RLCs, but also the loose primary particles effectively.

Facile formulation and fabrication of the cathode using a self-lithiated carbon for all-solid-state batteries

We propose a innovative concept to boost the electrochemical performance of cathode composite electrodes using surface-modified carbons with hydrophilic moieties to increase their dispersion in a Lithium Nickel Manganese Cobalt Oxide (NMC) cathode and in-situ generate Li-rich carbon surfaces. Using a rapid aqueous process, the hydrophilic carbon is effectively dispersed in NMC particles followed by the conversion of its acid surface groups (e.g. –COOH), which interact with the NMC particles due to their basicity, into grafted Li salt (–COO⁻Li⁺). The solid-state batteries prepared using the cathode composites with surface-modified carbon exhibit better electrochemical performance. Such modified carbons led to a better electronic conduction path as well as facilitating Li⁺ ions transfer at the carbon/NMC interface due to the presence of lithiated carboxylate groups on their surface.

Surface double coating of a LiNiaCobAl1−a−bO2 (a > 0.85) cathode with TiOx and Li2CO3 to apply a water-based hybrid polymer binder to Li-ion batteries

Recently a water-based polymer binder has been getting much attention because it simplifies the production process of lithium ion batteries (LIBs) and reduce their cost. The surface of LiNi_aCo_bAl_1−a−bO₂ (a > 0.85, NCA) cathode with a high voltage and high capacity was coated doubly with water-insoluble titanium oxide (TiO_x) and Li₂CO₃ layers to protect the NCA surface from the damage caused by contacting with water during its production process. The TiO_x layer was at first coated on the NCA particle surface with a tumbling fluidized-bed granulating/coating machine for producing TiO_x-coated NCA. However, the TiO_x layer could not coat the NCA surface completely. In the next place, the coating of the TiO_x-uncoated NCA surface with Li₂CO₃ layer was conducted by bubbling CO₂ gas in the TiO_x-coated NCA aqueous slurry on the grounds that Li₂CO₃ is formed through the reaction between CO₃²⁻ ions and residual LiOH on the TiO_x-uncoated NCA surface, resulting in the doubly coated NCA particles (TiO_x/Li₂CO₃-coated NCA particles). The Li₂CO₃ coating is considered to take place on the TiO_x layer as well as the TiO_x-uncoated NCA surface. The results demonstrate that the double coating of the NCA surface with TiO_x and Li₂CO₃ allows for a high water-resistance of the NCA surface and consequently the TiO_x/Li₂CO₃-coated NCA particle cathode prepared with a water-based binder possesses the same charge/discharge performance as that obtained with a “water-uncontacted” NCA particle cathode prepared using the conventional organic solvent-based polyvinylidene difluoride binder.

Recently a water-based polymer binder has been getting much attention because it simplifies the production process of lithium ion batteries (LIBs) and reduce their cost.