Ni-rich LiNi0.8Co0.1Mn0.1O2 layered oxide cathodes have been highlighted for large-scale energy applications due to their high energy density. Although its specific capacity is enhanced at higher voltages as Ni ratio increases, its structural degradation due to phase transformations and lattice distortions during cycling becomes severe. For these reasons, we focused on the origins of crack generation from phase transformations and structural distortions in Ni-rich LiNi0.8Co0.1Mn0.1O2 using multiscale approaches, from first-principles to meso-scale phase-field model. Atomic-scale structure analysis demonstrated that opposite changes in the lattice parameters are observed until the inverse Li content x = 0.75; then, structure collapses due to complete extraction of Li from between transition metal layers. Combined-phase investigations represent the highest phase barrier and steepest chemical potential after x = 0.75, leading to phase transformations to highly Li-deficient phases with an inactive character. Abrupt phase transformations with heterogeneous structural collapse after x = 0.81 (~220 mAh g−1) were identified in the nanodomain. Further, meso-scale strain distributions show around 5% of anisotropic contraction with lower critical energy release rates, which cause not only micro-crack generations of secondary particles on the interfaces between the contracted primary particles, but also mechanical instability of primary particles from heterogeneous strain changes.

Solid-state electrolytes based on ionic liquids and a gelling matrix are promising for rechargeable lithiumion batteries due to their safety under diverse operating conditions, favorable electrochemical and thermal properties, and wide processing compatibility. However, gel electrolytes also suffer from low mechanical moduli, which imply poor structural integrity and thus an enhanced probability of electrical shorting, particularly under conditions that are favorable for lithium dendrite growth. Here, we realize high-modulus, ion-conductive gel electrolytes based on imidazolium ionic liquids and exfoliated hexagonal boron nitride (hBN) nanoplatelets. Compared to conventional bulk hBN microparticles, exfoliated hBN nanoplatelets improve the mechanical properties of gel electrolytes by 2 orders of magnitude (shear storage modulus ∼5 MPa), while retaining high ionic conductivity at room temperature (>1 mS cm −1 ). Moreover, exfoliated hBN nanoplatelets are compatible with high-voltage cathodes (>5 V vs Li/Li + ) and impart exceptional thermal stability that allows high-rate operation of solid-state rechargeable lithium-ion batteries at temperatures up to 175 °C.

Lithium-rich oxide materials are promising candidates for high-energy lithium ion batteries, but currently have critical challenges of poor cycle performance and voltage drop induced by undesirable phase transformation. To resolve these problems, it is necessary to identify the origins and mechanism of phase transformation in Li 2 MnO 3 , a key component of Li-rich oxides. In this work, the phase transformation of bulk Li 2 MnO 3 is investigated by thermodynamic and kinetic approaches based on first-principles calculations and validated by experiments. Using the calculated thermodynamic energies, the most stable structure is determined as a function of Li extraction for Li 2Àx MnO 3 : monoclinic (x ¼ 0.0-0.75), layered-like (x ¼ 1.0-1.25), and spinel-like (x ¼ 1.5-2.0) structures. The phase transformation becomes kinetically possible for Li 2Àx MnO 3 (x > 1.0). Atomic scale origins and the mechanism of phase transformation are elucidated by the thermodynamically stable and kinetically movable tetrahedral coordination of Mn 4+ in the transition state. These theoretical observations are validated by ex situ X-ray photoelectron spectroscopy combined with electrochemical experiments for Li 2Àx MnO 3 with various Li contents upon cycling. The mechanistic understanding from theoretical calculations and experimental observations is expected to provide a fundamental solution and guidelines for improving the electrochemical performance of Li-rich oxides and, by extension, the battery performance.

As a promising hybrid energy storage system, lithium ion capacitors (LICs) have been intensively investigated regarding their practical use in various applications, ranging from portable electronics to grid support. The asymmetric LIC offers high-energy and high-power densities compared with conventional energy storage systems such as electrochemical double-layer capacitors (EDLCs) and lithium ion batteries (LIBs). To enable suitable operation of the LIC, the negative electrode should be pre-lithiated prior to cell operation, which is regarded as a key technology for developing self-sustainable LICs. In this work, we have demonstrated the potential use of Li 6 CoO 4 as an alternative lithium source to metallic lithium. A large amount of Li + can be electrochemically extracted from the structure incorporated into the positive electrode via a highly irreversible process. Most of the extracted Li + is available for pre-lithiation of the negative electrode during the first charge. This intriguing electrochemical behaviour of Li 6 CoO 4 is suitable for providing sufficient Li + to the negative electrode. To obtain a fundamental understanding of this system, the electrochemical behaviour and structural stability of Li 6 CoO 4 is thoroughly investigated by means of electrochemical experiments and theoretical validation based on first principles calculations.

By preventing electrical contact between anode and cathode electrodes while promoting ionic transport, separators are critical components in the safe operation of rechargeable battery technologies. However, traditional polymer-based separators have limited thermal stability, which has contributed to catastrophic thermal runaway failure modes that have conspicuously plagued lithium-ion batteries. Here, we describe the development of phase-inversion composite separators based on carbon-coated hexagonal boron nitride (hBN) nanosheets and poly­(vinylidene fluoride) (PVDF) polymers that possess high porosity, electrolyte wettability, and thermal stability. The carbon-coated hBN nanosheets are obtained through a scalable liquid-phase shear exfoliation method using ethyl cellulose as a polymer stabilizer and source of the carbon coating following thermal pyrolysis. When incorporated within the PVDF matrix, the carbon-coated hBN nanosheets promote favorable interfacial interactions during the phase-inversion process, resulting in porous, flexible, free-standing composite separators. The unique chemical composition of these carbon-coated hBN separators implies high wettability for a wide range of liquid electrolytes. This combination of high porosity and electrolyte wettability enables enhanced ionic conductivity and lithium-ion battery electrochemical performance that exceeds incumbent polyolefin separators over a wide range of operating conditions. The hBN nanosheets also impart high thermal stability, providing safe lithium-ion battery operation up to 120 °C.

Through first-principles calculations and experimental observations, we first present the correlation between the Ni and Mn ratio and the redox behaviors of the layered NCM cathodes. The equilibrium potentials based on redox reactions of Ni 2+ /Ni 3+ are highly dependent on the Mn ratio (NCM523 and NCM721: ∼3.7 and 3.5 V) because of a donor electron, in the e g band, transferred from Mn to Ni owing to their crystal field splitting (CFS) with different electronegativities, leading to oxidation states of Ni 2+ -like and Mn 4+ . Considering the electronic donor (Mn) based on CFS with electronegativity of transition metals (TMs), we finally expect V as a promising doping source to provide donor electrons for Ni redox reactions in Ni-rich layered oxides, leading to be higher delithiation potentials (NCV523: 3.8 V). From our theoretical calculations in the NCV oxide, the oxidation states of Ni and V are stable Ni 2+ -like and V 5+ , respectively, and the fractional d-band fillings of Ni are the highest value as compared with NCM523 and LiNiO 2 because of two donor electrons in the t 2g band. Based on the underlying understanding on the CFS with electronegativity of TMs, it would be possible to design new Ni-rich layered cathodes with higher energy for use in Li-ion batteries.

To achieve the high energy densities demanded by emerging technologies, lithium battery electrodes need to approach the volumetric and specific capacity limits of their electrochemically active constituents, which requires minimization of the inactive components of the electrode. However, a reduction in the percentage of inactive conductive additives limits charge transport within the battery electrode, which results in compromised electrochemical performance. Here, we introduce an electrode design that achieves efficient electron and lithium-ion transport kinetics at exceptionally low conductive additive levels and industrially relevant active material areal loadings. Using a scalable Pickering emulsion approach, Ni-rich LiNi 0.8 Co 0.15 Al 0.05 O 2 cathode powders are conformally coated using only 0.5 wt% of solution-processed graphene, resulting in an electrical conductivity that is comparable to 5 wt% carbon black. Moreover, the conformal graphene coating mitigates degradation at the cathode surface, thus This article is protected by copyright. All rights reserved.3 providing improved electrochemical cycle life. The morphology of the electrodes also facilitates rapid lithium-ion transport kinetics, which provides superlative rate capability.Overall, this electrode design concurrently approaches theoretical volumetric and specific capacity limits without tradeoffs in cycle life, rate capability, or active material areal loading.

Liquid-phase exfoliation of layered solids holds promise for the scalable production of 2D nanosheets. When combined with suitable solvents and stabilizing polymers, the rheology of the resulting nanosheet dispersions can be tuned for a variety of additive manufacturing methods. While significant progress is made in the development of electrically conductive nanosheet inks, minimal effort is applied to ion-conductive nanosheet inks despite their central role in energy storage applications. Here, the formulation of viscosity-tunable hexagonal boron nitride (hBN) inks compatible with a wide range of printing methods that span the spectrum from low-viscosity inkjet printing to high-viscosity blade coating is demonstrated. The inks are prepared by liquid-phase exfoliation with ethyl cellulose as the polymer dispersant and stabilizer. Thermal annealing of the printed structures volatilizes the polymer, resulting in a porous microstructure and the formation of a nanoscale carbonaceous coating on the hBN nanosheets, which promotes high wettability to battery electrolytes. The final result is a printed hBN nanosheet film that possesses high ionic conductivity, chemical and thermal stability, and electrically insulating character, which are ideal characteristics for printable battery components such as separators. Indeed, lithium-ion battery cells based on printed hBN separators reveal enhanced electrochemical performance that exceeds commercial polymer separators.