Layered oxide cathodes for lithium-ion batteries typically undergo large expansion and contraction during cycling, including a particularly abrupt shrinkage along the c lattice (c-collapse) at high states of charge, which limits their lifetime. Here we suppress the c-collapse in compositionally simple LiNi0.9Mn0.1O2 by electrochemically inducing partial disorder that is permanently retained throughout the bulk. Our approach leverages irreversible oxygen oxidation in Li-excess Ni-rich oxides to activate partial disordering of the cation sublattice, while preserving the long-range layered structure. By varying the initial Li-excess, we obtain Li-stoichiometric transition-metal oxides with tunable cation disorder. Surprisingly, when the concentration of transition-metal ions occupying Li sites (TMLi) reaches >= 12%, the c-lattice parameter remains nearly invariant during (de)lithiation, reducing chemical strain, preserving microstructural integrity and extending battery cycle life. The resulting material displays high specific capacity, long-term stability, small voltage hysteresis and negligible voltage decay. This concept opens the possibility of designing materials by inducing persistent intrinsic disorder electrochemically.

This study investigates a strategy to simultaneously enhance oxygen and cationic (Ni) redox reactions in Li2MnO3-based Li-rich cathode materials composed of LiNi0.5Mn0.5O2 (LNMO) and Li2MnO3 phases. It is demonstrated that high-temperature synthesis, particularly at 900 degrees C, promotes stabilization of the LNMO-like phase over the Li2MnO3-like phase, enabling concurrent activation of both redox reactions. The increased fraction of the LNMO-like phase significantly enhances the Ni redox reaction and raises the average discharge voltage. At the same time, the LNMO-like phase stabilization increases Ni incorporation into the Li2MnO3-like phase, which is crucial for activating the oxygen redox reaction. As a result, the material synthesized at 900 degrees C can achieve both high capacity and elevated discharge voltage. Additionally, the ratio of Li2MnO3 to NiO at 900 degrees C strongly influences redox reactions through its effect on the LNMO-like phase stabilization. While increasing NiO amount almost linearly enhances the Ni redox reaction, the oxygen redox reaction depends primarily on the Ni content incorporated into the Li2MnO3-like phase rather than its quantity. Therefore, simultaneous optimization of both redox reactions is achieved only within a specific compositional range, which can achieve certain amount of the Ni into the Li2MnO3-like phase. These findings demonstrate the phase stabilization control as an effective design strategy for high-energy-density Li2MnO3-based Li-rich layered materials.

Virtually all layered oxide positive electrodes (cathodes) for lithium-ion batteries exhibit abrupt shrinkage along the c lattice (c-collapse) at high states-of-charge, limiting cycle life. In this work, we suppress c-collapse by electrochemically inducing partial disorder permanently throughout the bulk of compositionally-simple LiNi0.9Mn0.1O2. Our approach leverages irreversible oxygen oxidation in the as-synthesized Li-excess Ni-rich oxides to activate partial disordering of the cation sublattice, while preserving the long-range layered structure. Using this method, Li-stoichiometric transition metal oxides with variable extents of cation disorder are readily fabricated by adjusting the starting Li-excess in the as-synthesized materials. Surprisingly, at a TMLi concentration of ≥12%, the c lattice parameter remains nearly invariant during (de)lithiation, leading to decreased chemical strain, enhanced microstructural integrity, and improved battery cycle life. We demonstrate a combination of high specific capacity and long cycle life, along with negligible voltage hysteresis and decay. This concept opens the opportunity for designing materials by inducing persistent intrinsic disorder electrochemically.

Developing stable and efficient electrocatalysts is vital for boosting oxygen evolution reaction (OER) rates in sustainable hydrogen production. High-entropy oxides (HEOs) consist of five or more metal cations, providing opportunities to tune their catalytic properties toward high OER efficiency. This work combines theoretical and experimental studies to scrutinize the OER activity and stability for spinel-type HEOs. Density functional theory confirms that randomly mixed metal sites show thermodynamic stability, with intermediate adsorption energies displaying wider distributions due to mixing-induced equatorial strain in active metal-oxygen bonds. The rapid sol-flame method is employed to synthesize HEO, comprising five 3d-transition metal cations, which exhibits superior OER activity and durability under alkaline conditions, outperforming lower-entropy oxides, even with partial surface oxidations. The study highlights that the enhanced activity of HEO is primarily attributed to the mixing of multiple elements, leading to strain effects near the active site, as well as surface composition and coverage.

Li- and Mn-rich (LMR) layered oxide positive electrode materials exhibit high energy density and have earth abundant compositions relative to conventional Ni-, Mn-, and Co-oxides (NMCs). The lithiation of coprecipitated precursors is a key part of synthesis and offers opportunities for tuning the properties of LMR materials. Whereas the morphology of transition metal precursors has received substantial attention, that of Li sources has not. Using Li1.14Mn0.57Ni0.29O2 as a model system, in this work we establish a detailed understanding of LMR calcination pathways via in situ and ex situ diffraction, spectroscopy, microscopy and thermogravimetry. Our work shows that large Li2CO3 particle size modulates a previously misunderstood thermogravimetric feature present at the Li2CO3 melting point during layered oxide calcination and causes heterogeneity at larger length scales (inter-secondary particle) than previously reported (intra-secondary particle). This work highlights the sensitivity of layered oxide calcination pathways to synthesis conditions and suggests design rules to minimize calcination heterogeneity in layered oxides beyond LMR.

Li-rich layered materials that have Co-free and Mn-rich 3d-transition metals have the potential to increase the achievable energy density of batteries because they are inexpensive and yield high capacity by exploiting an additional oxygen redox reaction. However, these have low electrochemical activity and sustainability, with severe voltage fade, rapid capacity decay, and poor rate capability. Here, we report sustainable cycling stability and fast rate capability of Co-free Li2MnO3-based Li-rich layered materials that are governed by the electrochemical activation process during the 1st cycle and that this process can be controlled by the degree of the cation disordering in the pristine material. From the comparative study of two samples that have different degrees of cation disordering in the same composition, an increase in cation disordering in the pristine material strongly improves its tolerance to structural changes in the bulk and on the surface during the activation process at the 1st cycle, leading to less structural changes for subsequent cycles. As a result, high electrochemical activity and superior rate capability in subsequent cycles can be achieved even with the cation disordering in the pristine. Furthermore, we verified the findings by developing an additional material that had higher cation disordering in the pristine structure than the samples tested and showing that the additional sample has improved rate capability and cycle retention. This understanding that sustainable electrochemical characteristics are governed by an activation process in the 1st cycle, which can be controlled by a structural feature of the pristine material, will be useful in the design of low-cost, Li-rich layered materials that can achieve sustainable high energy density and fast rate capability for Li-ion batteries.

The ultrafine-grained Ni-enriched Li[Ni0.95Co0.04Mo0.01]O2 (NCMo95) cathode achieved by inhibiting particle coarsening imparts the necessary mechanical toughness and significantly extends the battery life.

Co-free Mn-based Li-rich layered materials have been attracting a lot of attention due to their high capacity via the additional oxygen redox reaction and their low cost. However, their poor capacity retention and voltage fade upon cycling remains a problem for practical applications. Herein, we report on long-term cyclability of a Co-free Mn-based Li-rich layered material with superior voltage retention for 490 cycles. The developed one-step solid-state reaction, which comprises a thorough mixing and a heating process at high temperature followed by a quenching process, can increase substantially the amount of Ni incorporated into the Li2MnO3 phase, and thereby the resulting material has a robust layered structure caused by the increase in the cation disordering, and a facile electron transfer for the oxygen redox reaction leading to the remarkably improved oxygen redox reversibility for long-term cycles. The findings will provide a new strategy for achieving high performance for long-term cycles in Li-rich layered materials.

The quest for high energy density and high power density electrode materials for lithium-ion batteries has been intensified to meet strongly growing demand for powering electric vehicles. Conventional layered oxides such as Co-rich LiCoO2 and Ni-rich Li(NixMnyCoz)O-2 that rely on only transition metal redox reaction have been faced with growing constraints due to soaring price on cobalt. Therefore, Mn-rich electrode materials excluding cobalt would be desirable with respect to available resources and low cost. Here, the strategy of achieving both high energy density and high power density in Mn-rich electrode materials by controlling the solubility of atoms between phases in a composite is reported. The resulting Mn-rich material that is composed of defective spinel phase and partially cation-disordered layered phase can achieve the highest energy density, approximate to 1100 W h kg(-1) with superior power capability up to 10C rate (3 A g(-1)) among other reported Mn-rich materials. This approach provides new opportunities to design Mn-rich electrode materials that can achieve high energy density and high power density for Li-ion batteries.

Ni-rich layered electrode materials have attracted great attention as a promising cathode candidate for high-energy-density lithium-ion batteries because of their high capacity and relatively low cost. However, they have been suffering from severe capacity fading for cycles, which can originate from several factors such as the phase transition at the end of charge and disintegration of the particles. Herein, a simple and novel sublimation-induced gas-reacting (SIGR) process has been developed by using elemental sulfur to conformally coat Ni-rich layered materials. The sublimated gas-phase S can react with detrimental residual Li compounds on the surface of the particles. As a result, the reacted layer of LixSyOz phases forms on the outside of the secondary particles and simultaneously in the boundaries between primary particles inside the secondary particles. Compared to other reported surface modification processes, the SIGR-treated Ni-rich materials show substantially increased capacity retention and superior voltage retention by protecting the surface from the electrolyte and mitigating disintegration of the secondary particles. The SIGR process is a simple and scalable solid-state reaction at low temperature to improve the cycling stability of high-capacity Ni-rich electrode materials.

AbstractTo meet the growing demand for global electrical energy storage, high‐energy‐density electrode materials are required for Li‐ion batteries. To overcome the limit of the theoretical energy density in conventional electrode materials based solely on the transition metal redox reaction, the oxygen redox reaction in electrode materials has become an essential component because it can further increase the energy density by providing additional available electrons. However, the increase in the contribution of the oxygen redox reaction in a material is still limited due to the lack of understanding its controlled parameters. Here, it is first proposed that Li‐transition metals (TMs) inter‐diffusion between the phases in Li‐rich materials can be a key parameter for controlling the oxygen redox reaction in Li‐rich materials. The resulting Li‐rich materials can achieve fully exploited oxygen redox reaction and thereby can deliver the highest reversible capacity leading to the highest energy density, ≈1100 Wh kg−1 among Co‐free Li‐rich materials. The strategy of controlling Li/transition metals (TMs) inter‐diffusion between the phases in Li‐rich materials will provide feasible way for further achieving high‐energy‐density electrode materials via enhancing the oxygen redox reaction for high‐performance Li‐ion batteries.

We determined how Li doping affects the Ni/Mn ordering in high-voltage spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) by using neutron diffraction, TEM image, electrochemical measurements, and NMR data. The doped Li occupies empty octahedral interstitials (16c site) before the ordering transition, and can move to normal octahedral sites (16d (4b) site) after the transition. This movement strongly affects the Ni/Mn ordering transition because Li at 16c sites blocks the ordering transition pathway and Li at 16d (4b) sites affects electrostatic interactions with transition metals. As a result, Li doping increases in the Ni/Mn disordering without the effect of Mn 3+ ions even though the Li-doped LNMO undergoes order-disorder transition at 700 °C. Li doping can control the amount of Ni/Mn disordering in the spinel without the negative effect of Mn 3+ ions on the electrochemical property.

To quantify the effect of high voltage on the electrochemical properties of high-potential spinel ordered-LiNi0.5Mn1.5O4, it was intentionally exposed to 5.3V for 100h that can ensure the decomposition of electrolyte. After this treatment, the bulk structure did not change, but electrochemical properties of the sample were severely degraded; polarization became large and capacity loss was substantial. Polarization was caused by formation of a thick insulating passivation layer on the surface of the sample that was measured by impedance spectroscopy. The capacity loss can be partially caused by incomplete phase transformation during discharging as a result of loss of electrical contact due to the presence of the thick passivation layer on the surface of particles. This indicates that the phase transformation depends on the applied current. The other cause for the capacity loss can be from the inactiveness of transition metals in the surface that was measured by XPS. Thick passivation layer on the surface can have inactive transition metals leading to permanent capacity fading. Hence, to control the electrode stability in high voltage spinel LiNi0.5Mn1.5O4, a bare LNMO sample coated with Al2O3 by Atomic Layer Deposition (ALD) were prepared, then exposed to 5.3V for 100h. After this surface treatment, the Al2O3-coated sample showed much better electrochemical performance than the bare sample. During the exposure, the bare sample underwent intensive surface reactions with very large generated current density and large charge-transfer resistance. In contrast, the coated sample experienced much weaker surface reactions with low charge-transfer resistance even though the applied potential, 5.3V was much higher than the stable upper voltage limit (∼4.5V) of conventional electrolyte. The coating effectively protects the surface of the material from surface reactions such as oxidation of the electrolyte; therefore Al2O3-coated LNMO shows reasonable electrochemical properties after exposing at 5.3V for 100h. This finding demonstrates that detrimental effects of the exposure at high potential on the electrochemical properties strongly depends on surface characteristics. This understanding can be used to stabilize high-voltage positive electrode materials.

High energy density of a lithium ion battery (LIB) is an essential requirement for novel applications such as plug-in hybrid electric vehicles and electric vehicles. Increasing the redox potential of cathode materials is an effective way to achieve high energy density in the cell. For this purpose, high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode material for LIBs because it has a high redox potential of ~ 4.7 V, which makes its energy density (~650 W∙h/kg) 20% higher than that of conventional LiCoO2. However, the electrochemical properties of LNMO spinel depend on several factors such as its structure, the quantity of Mn3+ ions, the particle size, and the morphology of particles. Especially, the structure of the spinel has a critical influence on its electrochemical performance. LNMO structure is dictated by the ordering of Ni and Mn at two octahedral sites, which take two forms: disordered and ordered spinel. However, under typical experimental conditions, disordered spinel shows the disordering of Ni/Mn with the presence of Mn3+ ions, whereas ordered spinel shows the ordering of Ni/Mn without Mn3+ ions. As a result, electrochemical properties of the disordered spinel always depend on both the disordering of Ni/Mn and Mn3+ ions. For example, disordered spinel shows an extended solid-solution reaction during phase transformation whereas ordered spinel shows two distinct two-phases reactions. Furthermore, the presence of Mn3+ ions in the disordered spinel increases its electronic conductivity, and thereby improves its electrochemical performance. Therefore, disordered LNMO spinel can have better electrochemical performance than ordered spinel due to high electronic conductivity and facile phase transformation. The origin of the different electrochemical properties in the disordered spinel is not clear because of the coupling of the Ni/Mn disordering with Mn3+ ions. Understanding of this origin could guide improvement of LMNO’s electrochemical properties. However, experimentally understanding the effect of disordering or the effect of Mn3+ ions on the electrochemical properties is not easy because the Ni/Mn disordering is always coupled with the presence of Mn3+ ions. In this presentation, we will discuss the effect of the Ni/Mn disordering without the presence of Mn3+ on the electrochemical performance. At first, the Ni/Mn disordering was decoupled from the Mn3+ ions in this study. By using this decoupling, we will show how the Ni/Mn disordering affects electrochemical properties and the phase transformation behavior. Furthermore, we will discuss about key factors affecting superior rate capability in high voltage spinel by decoupling of the disordering from Mn3+ ions.

Electrochemical activity in high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is strongly affected by the disordering of Ni/Mn and the presence of Mn3+ ions. However, understanding the effect of the Ni/Mn disordering or the presence of Mn3+ ions on electrochemical properties is not trivial because disordering is typically coupled with the presence of Mn3+ ions. Here, we demonstrate for the first time that the doping of Li instead of Ni increases Ni/Mn disordering, which is decoupled from the presence of Mn3+ ions. The resultant material has a particle size of similar to 1-2 mu m and can achieve 120 mAh g(-1) at 10 C for 50 cycles and further deliver about 60 mAh g(-1) even at a rate of similar to 60 C (1 min discharge). Superior electrochemical performance is achieved by increased solid-solution phase transition behavior, which is caused by increased Ni/Mn disordering during delithiation. By decoupling, we find that the electrochemical properties in LNMO strongly depend on the phase transformation behavior and that the Ni/Mn disordering, rather than Mn3+ ions, affects the phase transformation by increasing the solid-solution reaction. The fundamental understanding gained from this work could be applied to the development of other phase-separating compounds to improve their electrochemical performance.