Influence of Calendering on the Electrochemical Performance of LiNi0.9Mn0.05Al0.05O2 Cathodes in Lithium-Ion Cells

Validating the Virtual Calendering Process With 3D-Reconstructed Composite Electrode: An Optimization Framework for Electrode Design

Calendering is an essential fabrication step for lithium-ion battery electrodes, aimed at achieving the target density through mechanical compression. During this process, the electrode's microstructure significantly deforms, affecting its electrochemical performance. Therefore, it is important to understand how the microstructure evolves during calendering and correlate these changes with electrochemical behavior. Despite tremendous experimental efforts, there are limitations in obtaining sufficient outcomes. In this regard, simulations offer valuable information; however, the highest priority is to develop a reliable modeling framework that reflects actual microstructural changes and establish a robust validating methodology. Without such a framework, computational predictions may not align with experimental results. This study develops a virtual calendering framework based on high-resolution FIB-SEM tomography images of a bimodal LiNi0.6Co0.2Mn0.2O2 cathode with a mass loading of 19.8 mg cm-2 and 96 wt.% active material. The framework is rigorously validated through systematically designed experiments across various electrode densities (2.3-4.0 g cm-3) and further analysis of hidden microstructural features, such as ionic tortuosity, contact area, and crack structure through additional tomography analysis. The virtual calendering framework successfully predicts microstructural changes and electrochemical performance, offering a reliable pathway for identifying optimal design parameters in a time- and cost-effective manner.

Electrolyte-Enabled High-Voltage Operation of a Low-Nickel, Low-Cobalt Layered Oxide Cathode for High Energy Density Lithium-Ion Batteries

The lithium-ion battery industry acknowledges the need to reduce expensive metals, such as cobalt and nickel, due to supply chain challenges. However, doing so can drastically reduce the overall battery energy density, attenuating the driving range for electric vehicles. Cycling to higher voltages can increase the capacity and energy density but will consequently exacerbate cell degradation due to the instability at high voltages. Herein, an advanced localized high-concentration electrolyte (LHCE) is utilized to enable long-term cycling of a low-Ni, low-Co layered oxide cathode LiNi0.60Mn0.31Co0.07Al0.02O2 (NMCA) in full cells with graphite or graphite-silicon anodes at 4.5 V (≈4.6 vs Li+/Li). NMCA cells with the LHCE deliver a high initial capacity of 194 mA h g-1 at C/10 rate along with 73% capacity retention after 400 cycles compared to 49% retention in a baseline carbonate electrolyte. This is facilitated by reduced impedance growth, active material loss, and gas evolution with the NMCA cathode. These improvements are attributed to the formation of robust, inorganic-rich interphase layers on both the cathode and anode throughout cycling, which are induced by a favorable salt decomposition in the LHCE. This study demonstrates the efficacy of electrolytes toward facilitating the operation of high-energy-density, long-life, and cost-effective cathodes.

Efficacy of atomic layer deposition of Al2O3 on composite LiNi0.8Mn0.1Co0.1O2 electrode for Li-ion batteries

LiNi0.8Mn0.1Co0.1O2 (NMC811) is a popular cathode material for Li-ion batteries, yet degradation and side reactions at the cathode-electrolyte interface pose significant challenges to their long-term cycling stability. Coating LiNixMnyCo1-x-yO2 (NMC) with refractory materials has been widely used to improve the stability of the cathode-electrolyte interface, but mixed results have been reported for Al2O3 coatings of the Ni-rich NMC811 materials. To elucidate the role and effect of the Al2O3 coating, we have coated commercial-grade NMC811 electrodes with Al2O3 by the atomic layer deposition (ALD) technique. Through a systematic investigation of the long-term cycling stability at different upper cutoff voltages, the stability against ambient storage, the rate capability, and the charger transfer kinetics, our results show no significant differences between the Al2O3-coated and the bare (uncoated) electrodes. This highlights the contentious role of Al2O3 coating on Ni-rich NMC cathodes and calls into question the benefits of coating on commercial-grade electrodes.

Origins and Importance of Intragranular Cracking in Layered Lithium Transition Metal Oxide Cathodes

Li-ion batteries have a pivotal role in the transition toward electric transportation. Ni-rich layered transition metal oxide (LTMO) cathode materials promise high specific capacity and lower cost but exhibit faster degradation compared with lower Ni alternatives. Here, we employ high-resolution electron microscopy and spectroscopy techniques to investigate the nanoscale origins and impact on performance of intragranular cracking (within primary crystals) in Ni-rich LTMOs. We find that intragranular cracking is widespread in charged specimens early in cycle life but uncommon in discharged samples even after cycling. The distribution of intragranular cracking is highly inhomogeneous. We conclude that intragranular cracking is caused by local stresses that can have several independent sources: neighboring particle anisotropic expansion/contraction, Li- and TM-inhomogeneities at the primary and secondary particle levels, and interfacing of electrochemically active and inactive phases. Our results suggest that intragranular cracks can manifest at different points of life of the cathode and can potentially lead to capacity fade and impedance rise of LTMO cathodes through plane gliding and particle detachment that lead to exposure of additional surfaces to the electrolyte and loss of electrical contact.

A Comprehensive Review of In Situ Measurement Techniques for Evaluating the Electro-Chemo-Mechanical Behaviors of Battery Electrodes

The global production landscape exhibits a substantial need for efficient and clean energy. Enhancing and advancing energy storage systems are a crucial avenue to optimize energy utilization and mitigate costs. Lithium batteries are the most effective and impressive energy utilization system at present, with good safety, high energy density, excellent cycle performance, and other advantages, occupying most of the market. However, due to the defects in the electrode material of the battery itself, the electrode will undergo the process of expansion, stress evolution, and electrode damage during electro-chemical cycling, which will degrade battery performance. Therefore, the detection of property changes in the electrode during electro-chemical cycling, such as the evolution of stress and the modulus change, are useful for preventing the degradation of lithium-ion batteries. This review presents a current overview of measurement systems applied to the performance detection of batteries' electrodes, including the multi-beam optical stress sensor (MOSS) measurement system, the digital image correlation (DIC) measurement system, and the bending curvature measurement system (BCMS), which aims to highlight the measurement principles and advantages of the different systems, summarizes a part of the research methods by using each system, and discusses an effective way to improve the battery performance.

Design of an Online Electrochemical Mass Spectrometry System to Study Gas Evolution from Cells with Lean and Volatile Electrolytes

Gas evolution in high-energy Li-ion batteries remains a pervasive problem for a multitude of chemistries, jeopardizing the electrochemical performance and safety for consumers of electric vehicles. Many electrode-electrolyte degradation processes evolve gasses that may be detected in-situ with online electrochemical mass spectrometry (OEMS). In this work, details are provided for the setup and validation of an OEMS system that operates well under lean and volatile electrolyte conditions. Quite notably, the OEMS cells with only 40 µL of electrolyte and intermittent headspace sampling exhibit comparable electrochemical performance to flooded coin-cells. It is demonstrated that the onset time, shape, and magnitude of the gas evolution profiles calculated from mass spectrometer measurements match well to a known pressure reference through the use of an empirically determined fraction of removal. The off-gassing characteristics from a set of layered-oxide materials, NMC532, NMC811, and LNO, are used to further validate the OEMS setup against the literature. It is shown that many of the features present in the OEMS curves for equivalent systems from other groups are captured by this OEMS system. At an upper cut-off voltage of 4.4 V, LNO exhibits an intense release of CO₂ , O₂ , and CO gas relative to NMC532 and NMC811.

Realization of High Loading Density Lithium Polymer Batteries by Optimizing Lithium-Ion Transport and Electronic Conductivity

Lithium polymer batteries (LPBs) with a high energy density and safety are being actively studied for their use as an energy storage system. However, bottlenecks to their development include charge-transport resistance and poor interfacial contact. In this paper, we introduce carbon nanofiber (CNF) as a conductive additive and the optimization of porosity in the electrode by calendering to realize a high loading density LPB. A simple dispersion strategy is applied to homogeneously disperse nanofiber additives in the electrode to achieve high electronic conductivity. Calendering with optimized pressing degree was performed on the CNF-based electrode to enhance lithium-ion transport and electron conduction in the LPB. The optimal pressing conditions were confirmed by measuring the electronic conductivity, internal resistance, lithium-ion diffusion coefficient, and charge transport characteristics of the cells. When the electrode was pressed by 35%, optimum electrode wettability by solid polymer electrolyte and contact between particles and current collector were achieved, resulting in the high performance of the LPB. Finally, at the optimized pressing degree, we successfully demonstrate 90% cycle retention during 100 cycles and an improvement of the volumetric energy density by over seven-fold.

Opportunities and Challenges of Li2 C4 O4 as Pre-Lithiation Additive for the Positive Electrode in NMC622||Silicon/Graphite Lithium Ion Cells

Silicon (Si)-based negative electrodes have attracted much attention to increase the energy density of lithium ion batteries (LIBs) but suffer from severe volume changes, leading to continuous re-formation of the solid electrolyte interphase and consumption of active lithium. The pre-lithiation approach with the help of positive electrode additives has emerged as a highly appealing strategy to decrease the loss of active lithium in Si-based LIB full-cells and enable their practical implementation. Here, the use of lithium squarate (Li2 C4 O4 ) as low-cost and air-stable pre-lithiation additive for a LiNi0.6 Mn0.2 Co0.2 O2 (NMC622)-based positive electrode is investigated. The effect of additive oxidation on the electrode morphology and cell electrochemical properties is systematically evaluated. An increase in cycle life of NMC622||Si/graphite full-cells is reported, which grows linearly with the initial amount of Li2 C4 O4 , due to the extra Li+ ions provided by the additive in the first charge. Post mortem investigations of the cathode electrolyte interphase also reveal significant compositional changes and an increased occurrence of carbonates and oxidized carbon species. This study not only demonstrates the advantages of this pre-lithiation approach but also features potential limitations for its practical application arising from the emerging porosity and gas development during decomposition of the pre-lithiation additive.

From Materials to Cell: State-of-the-Art and Prospective Technologies for Lithium-Ion Battery Electrode Processing

Electrode processing plays an important role in advancing lithium-ion battery technologies and has a significant impact on cell energy density, manufacturing cost, and throughput. Compared to the extensive research on materials development, however, there has been much less effort in this area. In this Review, we outline each step in the electrode processing of lithium-ion batteries from materials to cell assembly, summarize the recent progress in individual steps, deconvolute the interplays between those steps, discuss the underlying constraints, and share some prospective technologies. This Review aims to provide an overview of the whole process in lithium-ion battery fabrication from powder to cell formation and bridge the gap between academic development and industrial manufacturing.