Li-rich Phase Research Articles

Cobalt-free spinel–layered structurally integrated Li0.8Mn0.64Ni0.183Fe0.091O2 cathodes for lithium-ion batteries

Cobalt-free, Li-rich layered-spinel structurally integrated positive electrode (cathode) materials for lithium-ion batteries (LIBs), with nominal composition 0.6(Li1.2Mn0.56Fe0.08Ni0.16O2) 0.4(LiFe0.2Mn1.4Ni0.4O4) which can otherwise be written as Li0.8Mn0.64Ni0.183Fe0.091O2 (FeSL) are synthesized via simple citric acid-assisted sol-gel route. Four different final annealing temperatures (550 °C, 650 °C, 750 °C, and 850 °C) were chosen to investigate their influence on electrochemical performance. The obtained composite materials contain spinel (space group Fd3¯m) as well as Li-rich layered phases (space group C2/m) as revealed by X-ray diffraction (XRD), HRTEM and cyclic voltammetry investigations. The excellent electrochemical performance of the composite material could be attributed to the structural stability achieved by the integration of spinel and layered components. Selected synthesized composite materials exhibit high discharge capacities close to 200 mAh g−1. The FeSL750 shows better capacity retention (92(3)% at the 50th cycle and 82(5)% at the 70th cycle) and rate capability than the FeSL550 and FeSL650 samples. However, the FeSL850 sample shows different charge-discharge behaviour. The charge capacity corresponding to FeSL850 is found to increase up to the 20th cycle, then stabilizes and displays a capacity retention of almost 100 % at the 50th cycle and 91(1)% at the 70th cycle. The electrochemical mechanism of FeSL750 was elucidated via in operando XAS investigations, which reveal electrochemical activity from all transition metals.

(Invited) Operando Nanoimaging of Phase Transformations in Energy Storage Materials

We applied operando Bragg Coherent Diffractive Imaging (BCDI) to study the discontinuous phase transformation in LixNi0.5Mn1.5O4 embedded in a fully operational battery. During Li-intercalation, we observed nucleation and growth of the Li-rich phase in a 500 nm particle embedded in the multicomponent positive electrode. The data captures the evolution from a curved coherent to planar semi-coherent interface, driven by dislocation dynamics. These dislocations travel with the interface and are expelled upon the completion of the phase transformation, resulting in a crystal devoid of defects. We hypothesize that these defects move via glissile motion without diffusion of host ions. Our data indicate the absence of significant kinetic limitations affecting the transformation kinetics, even under rapid discharge within 2 hours. This study underscores the capability of BCDI as a powerful tool for operando analysis of nanoscale phase transformations, offering guidance for the design and optimization of electrochemical materials.

Phase transitions limit lithium adsorption in titanium-based ion sieves

Hydrogen titanium oxide (HTO) is a promising material in extracting lithium ions from dilute sources such as geothermal or oil/gas brines. However, experiments show limited Li adsorption in HTO compared to its theoretical maximum capacity, where all H atoms in HTO are replaced by Li that forms lithium titanium oxide (LTO). Here, ab initio molecular dynamics (AIMD) simulations show clear evidence of phase transitions at specific Li adsorption in pure or doped HTO/LTO, which directly predict their experimental maximum capacity. Analysis of thermodynamic properties as well as layered crystal structures show distinct Li-poor to Li-rich phase transitions in the pure, Mo-doped, and Fe-doped HTO/LTO. In addition, it is observed a second phase transition in the Fe-doped HTO/LTO in the Li-poor phases that further constrains Li adsorption. To the best of my knowledge, this is the first study that accurately predict the experimental capacities in ion sieves from first principle. More importantly, this study puts spotlights on phase transitions as an important consideration in molecular engineering developments of functional separation materials, such as the high-performance lithium-ion sieves presented herein.

Li-Site Defects Induce Formation of Li-Rich Impurity Phases: Implications for Charge Distribution and Performance of LiNi0.5- xMxMn1.5O4 Cathodes (M = Fe and Mg; x = 0.05-0.2).

An understanding of the structural properties that allow for optimal cathode performance, and their origin, is necessary for devising advanced cathode design strategies and accelerating the commercialization of next-generation cathodes. High-voltage, Fe- and Mg-substituted LiNi0.5Mn1.5O4 cathodes offer a low-cost, cobalt-free, yet energy-dense alternative to commercial cathodes. In this work, the effect of substitution on several important structure properties is explored, including Ni/Mn ordering, charge distribution, and extrinsic defects. In the cation-disordered samples studied, a correlation is observed between increased Fe/Mg substitution, Li-site defects, and Li-rich impurity phase formation-the concentrations of which are greater for Mg-substituted samples. This is attributed to the lower formation energy of MgLi defects when compared to FeLi defects. Li-site defect-induced impurity phases consequently alter the charge distribution of the system, resulting in increased [Mn3+] with Fe/Mg substitution. In addition to impurity phases, other charge compensators are also investigated to explain the origin of Mn3+ (extrinsic defects, [Ni3+], oxygen vacancies and intrinsic off-stoichiometry), although their effects are found to be negligible.

Unlocking room temperature formation of Li-rich phases in aluminum anodes for Li-ion batteries

Aluminum (Al) has been an attractive anode candidate for lithium-ion batteries (LIBs) since the 1970s. While the formation of β-LiAl is considered the origin of the Li storage capability in Al anodes, multiple Li-Al phases are known to exist which have even greater lithium content, and the most enriched phase offers twice the theoretical specific capacity of the β-LiAl phase (ca. 2,000 mAh g−1-Al). These Li-rich phases are often neglected in the field of electrochemical energy storage since they are generally believed to be only approachable at elevated temperatures. Here, we demonstrate for the first time that both Li3Al2 and Li2-xAl can readily form at room temperature, but only under extraordinarily slow rates, proving that their formation is largely kinetically limited. Although Li9Al4 also seems to exist, experimental evidence suggests that its formation is governed by a different mechanism than the other higher-ordered phases. With the constant interplay between diffusion and nucleation, we set out to map the behaviors of Al anodes at different temperatures and rates considering the formation of Li3Al2 and Li2-xAl. Also, systematic impedance spectroscopy is employed to shed light on the kinetical properties of these two phases, which seem very different from the well-studied β-LiAl, explaining why they were largely neglected in the field of LIBs. While these investigations are mostly consistent with earlier studies, further material characterizations are warranted to better understand how to utilize these Li-rich phases strategically, such that they may be employed in novel lithium-ion cells.

Enhancement effect of Li addition on nitriding reaction and combustion of Al-Li alloy in N2

For aluminum-based alloy particles, the addition of alloying element lithium (Li) with the properties of a high chemical activity and a low melting/boiling point can significantly improve the thermo-reactive properties of aluminum (Al) particles. To further reveal the combustion mechanism, this paper presents the nitriding reaction and combustion characteristics of Al-Li alloy in nitrogen (N2) through thermogravimetric analysis and differential scanning calorimetry (TG-DSC) analysis at a low heating rate and laser-induced ignition experiments at a high heating rate, considering the influences of two kinds of Li contents (1.0 wt% @ Al-1.0Li and 2.5 wt% @ Al-2.5Li) on these characteristics and making a comparison to the counterpart Al. Al-Li alloy powders as-prepared by gas atomization method showed the texture of the Li-rich eutectic phase compounds on the surface by scanning electron microscope (SEM) characterization. The TG-DSC results demonstrated that the thermal nitriding reaction of Al-Li alloy in N2 was significantly faster than that of pure Al. The nitriding reaction temperature decreased from 853 °C for pure Al to 245 °C for Al-2.5Li alloy with a reduction of 71 %. The final weight gain of Al-2.5Li alloy was almost three times higher than that of pure Al in N2. The SEM photograph of intermediate nitriding products revealed that the cracks and loose “island” structures in the Li-rich zone on the Al-Li surface were the key to preventing the formation of a “passivation effect” into Al and promoting N2 uptake during melting. In addition, Li also acts as a catalytic carrier and “oxygen absorber” to enhance the Al-N reaction. The combustion of single Al-Li alloy microparticles induced by laser showed two stages: preheating and rapid nitriding. Al-Li alloy particles were ignited more rapidly and showed typical gas-phase / surface combustion modes different from pure Al. According to these findings, the combustion mechanism was proposed to help guide the development of Al-based solid propellants containing Li and the synthesis of AlN/Al composites in nitrogen-rich environments.

Limiting cobalt fraction in lithium rich cathode materials for stable and fast activation

Li-rich layered oxides (LRLOs) have been considered as promising cathode materials for high-energy Li-ion batteries. However, considerable fractionsof costly Co and Ni are normally needed in LRLOs to access the high capacity. In this work, a series of Ni/Co-poor LRLOs is designed to study the effect of Ni:Co ratio on their electrochemical behavior. Due to the lowest-lying Co t2g band, the introduction of minor Co significantly promotes the activation of Li-rich phase. While high Co content exacerbates the interfacial reactions to form a thick and unstable cathode-electrolyte film. Consequently, the low-Co LRLO (ca. 4 % of transition metal) attains stable and fast activation, maintaining 233.3 mA h g−1 after 300 cycles at 1C. Moreover, the low-Co LRLO//graphite full cell retains 86.4 % of its capacity after 200 cycles. This work will shed light on the compositional design of LRLOs towards higher electrochemical performance and lower materials cost.

Review and Stress Analysis on the Lithiation Onset of Amorphous Silicon Films

This work aims to review and understand the behavior of the electrochemical lithiation onset of amorphous silicon (a-Si) films as electrochemically active material for new generation lithium-ion batteries. The article includes (i) a review on the lithiation onset of silicon films and (ii) a mechanochemical model with numerical results on the depth-resolved mechanical stress during the lithiation onset of silicon films. Recent experimental studies have revealed that the electrochemical lithiation onset of a-Si films involves the formation of a Li-poor phase (Li0.3Si alloy) and the propagation of a reaction front in the films. The literature review performed reveals peculiarities in the lithiation onset of a-Si films, such as (i) the build-up of the highest mechanical stress (up to 1.2 GPa) during lithiation, (ii) a linear increase in the mechanical stress with lithiation which mimics the characteristics of linear elastic deformation, (iii) only a minute volume increase during Li incorporation, which is lower than expected from the number of Li ions entering the silicon electrode, (iv) the largest heat generation appearing during cycling with only a minor degree of parasitic heat contribution, and (v) an unexpected enhanced brittleness. The literature review points to the important role of mechanical stresses in the formation of the Li-poor phase and the propagation of the reaction front. Consequently, a mechanochemical model consisting of two stages for the lithiation onset of a-Si film is developed. The numerical results calculated from the mechanochemical model are in good accord with the corresponding experimental data for the variations in the volumetric change with state of charge and for the moving speed of the reaction front for the lithiation of an a-Si film of 230 nm thickness under a total C-rate of C/18. An increase in the total C-rate increases the moving speed of the reaction front, and a Li-rich phase is likely formed prior to the end of the growth of the Li-poor phase at a high total C-rate. The stress-induced phase formation of the Li-poor phase likely occurs during the lithiation onset of silicon electrodes in lithium-ion battery.

Utilization of Li-Rich Phases in Aluminum Anodes for Improved Cycling Performance through Strategic Thermal Control

Lithium-ion batteries with aluminum anodes had appeared to resolve critical dendrite issues of lithium metal cells in the 1970s. However, the poor cycling performance attributed to aluminum anodes would lead to their obsolescence. In this work, we demonstrate how strategic thermal control in cycling aluminum anodes circumvents the problematic α/β phase transformations that yield poor cycling life. Instead, electrochemical formation of the Li3Al2 and Li2–xAl phases necessitates temperatures slightly above ambient, as the Li3Al2 and Li2–xAl phases are key enablers for high capacity and stable cycling. While delivering a competitive capacity level (ca. 1 Ah kg–1-Al), cycling among those higher-order phases is found to be significantly improved, from several cycles to 100 cycles with ca. 67% capacity retention. Importantly, because modern battery charging is likely to occur above room temperature due to ohmic heating, the thermal conditions explored here are expected to be realized in a variety of applications. Furthermore, we show that elevated temperature is not necessary for aluminum anode delithiation, thus creating additional synergies with many practical scenarios.

Simulating fracture patterns under anisotropic swelling in lithiated crystalline nanostructures

Various crystalline nanostructures, such as silicon nanowires and nanotubes are promising in high-capacity lithium-ion batteries due to their excellent fracture resistance. Progress has been notably made in studying the mechanical behaviors in these structures. However, understanding the dynamic fracture under anisotropic swelling still poses some challenges. Here we have developed a concurrently coupled chemo-mechanical model considering two-phase diffusion, elastic–plastic deformation, and crack growth based on peridynamics to simulate the dynamic behaviors in the core–shell nanostructures with coexisting Li-rich and Li-poor phases. Our model includes several key features observed in the experiments, including sharp phase interfaces, anisotropic interfacial migration velocities, lithiation-induced large deformation, and fracture-pattern formation. The chemo-mechanical simulations predict that cracks are formed and propagate between two adjacent <110> orientations. In addition, our simulations also demonstrate that, compared with solid nanowires, nanotubes can facilitate lithium-ion diffusion and better resist failure. Understanding the mechanisms of different fracture patterns under anisotropic swelling in nanowires and nanotubes provides a basis for the design of new failure-resistant nanostructures in the future.

Microstructure of the Li-Al-O Second Phases in Garnet Solid Electrolytes.

The microstructure of the Li7La3Zr2O12 (LLZO) garnet solid electrolyte is critical for its performance in all-solid-state lithium-ion battery. During conventional high-temperature sintering, second phases are generated at the grain boundaries due to the reaction between sintering aids and LLZO, which have an enormous effect on the performances of LLZO. However, a detailed structure study of the second phases and their impact on physical properties is lacking. Here, crystal structures of the second phases in LLZO pellets are studied in detail by transmission electron microscopy. Three different crystal structures of Li-Al-O second phases, γ-LiAlO2, α-Li5AlO4, and β-Li5AlO4 were identified, and atomic-scale lattice information was obtained by applying low-dose high-resolution imaging for these electron-beam-sensitive second phases. On this basis, the structure-property relationship of these structures was explored. It was found that sintering aids with a higher Li/Al ratio are beneficial to form Li-rich second phases, which result in more highly ionic conductive LLZO.

The decisive role of electrostatic interactions in transport mode and phase segregation of lithium ions in LiFePO4.

Understanding the mechanism of slow lithium ion (Li+) transport kinetics in LiFePO4 is not only practically important for high power density batteries but also fundamentally significant as a prototypical ion-coupled electron transfer process. Substantial evidence has shown that the slow ion transport kinetics originates from the coupled transfer between electrons and ions and the phase segregation of Li+. Combining a model Hamiltonian analysis and DFT calculations, we reveal that electrostatic interactions play a decisive role in coupled charge transfer and Li+ segregation. The obtained potential energy surfaces prove that ion-electron coupled transfer is the optimal reaction pathway due to electrostatic attractions between Li+ and e- (Fe2+), while prohibitively large energy barriers are required for separate electron tunneling or ion hopping to overcome the electrostatic energy between the Li+-e- (Fe2+) pair. The model reveals that Li+-Li+ repulsive interaction in the [010] transport channels together with Li+-e- (Fe2+)-Li+ attractive interaction along the [100] direction cause the phase segregation of Li+. It explains why the thermodynamically stable phase interface between Li-rich and Li-poor phases in LiFePO4 is perpendicular to [010] channels.

Effects of Li content on stability, electronic and Li-ion diffusion properties of Li&lt;sub&gt;3&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;La&lt;sub&gt;(2/3)–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;†&lt;sub&gt;(1/3)–2&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;TiO&lt;sub&gt;3&lt;/sub&gt; surface

Li&lt;sub&gt;3&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;La&lt;sub&gt;(2/3)–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;†&lt;sub&gt;(1/3)–2&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;TiO&lt;sub&gt;3&lt;/sub&gt;(LLTO) is a promising solid-state electrolyte for Li-ion batteries. We study the effect of Li content on the stability, electronic and Li-ion diffusion properties of LLTO surface based on first-principles and molecular dynamics simulations. We consider both Li-poor and Li-rich LLTO surfaces. The results show that La/O/Li-terminated LLTO (001) is the most stable crystal surface. Further, LLTO (001) surface gives better stability when Li content is 0.17, 0.29, and 0.38 for Li-poor phase, while 0.33, 0.40, and 0.45 for Li-rich phase . Electronic structure calculations infer that in both Li-poor and Li-rich LLTO(001) surfaces there occurs the transition from conductor to semiconductor with the increase of Li content. Besides, we find that Li-ion always keeps a two-dimensional diffusion path for different Li content. As Li content increases from 0.17 to 0.38 for Li-poor LLTO (001) surface, Li-ion diffusion coefficient increases gradually and Li-ion diffusion barrier decreases from 0.58 eV to 0.42 eV. Differently, when Li content increases from 0.33 to 0.45 for Li-rich LLTO(001) surface, it does not follow a monotonic trend for diffusion coefficient nor for diffusion barrier of Li-ion. In this case, Li-ion diffusion coefficient is the largest and Li-ion diffusion barrier is the lowest (0.30 eV) when Li content is 0.40. Thus, our study suggests that by varying Li content, the stability, band gap, and Li-ion diffusion performance of LLTO (001) can be changed favorably. These advantages can inhibit the formation of lithium dendrites on the LLTO (001) surface.

Fabrication of CeCl3/LiCl/CaCl2 Ternary Eutectic Scintillator for Thermal Neutron Detection

To date, 3He gas has been commonly used to detect thermal neutrons because of their high chemical stability and low sensitivity to γ-rays, owing to their low density and large neutron capture cross-section. However, the depletion of 3He gas prompts the development of a new solid scintillator for thermal neutron detection to replace 3He gas detectors. Solid scintillators containing 6Li are commonly used to detect thermal neutrons. However, they are currently used in single crystals only, and their 6Li concentration is defined by their chemical composition. In this study, 6Li-containing eutectic scintillators were developed. CeCl3 was selected as the scintillator phase because of its low density (3.9 g/cm3); high light yield (30,000 photons/MeV); and fast decay time with four components of 4.4 ns (6.6%), 23.2 ns (69.6%), 70 ns (7.5%) and &gt;10 μs (16.3%), owing to the Ce3+ 5d-4f emission peak at approximately 360 nm. Crystals of the CeCl3, LiCl and CaCl2 ternary eutectic were fabricated by the vertical Bridgman technique. The grown eutectic crystals exhibited Ce3+ 5d-4f emission with a peak at 360 nm. The light yield was 18,000 photons/neutron, and the decay time was 10.5 ns (27.7%) and 40.1 ns (72.3%). Therefore, this work demonstrates optimization by combining a scintillator phase and Li-rich matrix phase for high Li content, fast timing, high light yield and low density.

Structural evolution dependency on depth-of-discharge in VO2(B) Li-ion battery electrodes

Bronze vanadium oxide, VO2(B), has gained significant interest as electrode for Li-ion mainly due to the ease of preparation and the experimentally obtainable capacities of >325 mAh g−1 with intercalation of >1Li. In this work, we investigate for the first time the effects of intercalating >0.5Li on the structural phase evolution. Using operando X-ray diffraction, we find that deep discharge (i.e. inserting >0.7Li), has a dramatic effect on the subsequent charge process by introducing significant solid-solution behavior in the two-phase transition between the Li-rich and Li-poor phases. Rietveld refinement shows that the discharge-charge asymmetry is caused by severe structural deformations in the Li-rich state. Furthermore, we find that deep discharge causes capacity fade. This appears to be linked to the structural deformation causing an irreversible decrease in the Li-ion diffusion coefficients, determined herein by galvanostatic intermittent titrations.

A novel GP-Li precursor and the correlated precipitation behaviors in Al-Cu-Li alloys with different Cu/Li ratio

Aluminum-lithium (Al–Li) alloys have become an essential material for aircraft skin in the aerospace industry owing to their high strength and low density. An optimized coherent Cu/Li ratio and well controlled precipitation sequence are critical to upgrade the desired properties. In this study, we systematically evaluate the effect of the Cu/Li ratio (ranging from 0.5 to 1.4) on the aging hardening and precipitation behavior of Al–Cu–Li alloys with specific rare earth elements (Sc, Zr, and Ce). Using state-of-the-art aberration-corrected transmission electron microscopy equipped with super-energy-dispersive X-ray spectroscopy (EDS) and atomic scale spatially resolved electron energy loss spectroscopy (EELS) with K3 camera, classical strengthening phases, such as Cu containing precipitates T1 (Al2CuLi), θ′ (Al2Cu) and Li-rich phase δ′ (Al3Li), have been identified during the artificial aging and natural aging treatment. A new Li-rich phase (namely, the GP-Li zone) with a hexagonal shape has been identified in alloys with Cu/Li ratios of 0.5 and 1. High density GP-Li zones are formed after five months natural aging, which are found fully coherent with the Al matrix. The discovery of GP-Li zones shows a new precipitation path for Li atoms in the supersaturated solid solution. Besides, the GP-Li zone stimulates the nucleation of T1 and θ′ phase at the interfaces indicating that there is an alternative approach for the nucleation mechanism of T1 and θ′. The crossover between the suppression of δ′ phase formation and the acceleration of T1 and θ′ precipitation occurs when the Cu/Li ratio is increased during the artificial aging process, resulting in a decrease in the aging hardening ability at first, followed by a large recovery in aging hardening. The findings of this study provide a strategy to design high strength Al–Li alloys through the manipulation of Cu/Li ratios and the newly identified GP-Li phase.

Understanding the Degradation of a Model Si Anode in a Li-Ion Battery at the Atomic Scale.

To advance the understanding of the degradation of the liquid electrolyte and Si electrode, and their interface, we exploit the latest developments in cryo-atom probe tomography. We evidence Si anode corrosion from the decomposition of the Li salt before charge–discharge cycles even begin. Volume shrinkage during delithiation leads to the development of nanograins from recrystallization in regions left amorphous by the lithiation. The newly created grain boundaries facilitate pulverization of nanoscale Si fragments, and one is found floating in the electrolyte. P is segregated to these grain boundaries, which confirms the decomposition of the electrolyte. As structural defects are bound to assist the nucleation of Li-rich phases in subsequent lithiations and accelerate the electrolyte’s decomposition, these insights into the developed nanoscale microstructure interacting with the electrolyte contribute to understanding the self-catalyzed/accelerated degradation Si anodes and can inform new battery designs unaffected by these life-limiting factors.

Grain boundary metal–insulator transitions in polycrystalline LiCoO[formula omitted

A thermodynamically consistent variational framework is developed to show that the metal–insulator transition in polycrystalline LiCoO2 is driven by grain boundary lithium segregation, the interfacial misorientation, and the size of the abutting grains. In general, high-angle grain boundaries and grains possessing high curvature favor phase transformation to Li-rich phases. In particular, the insulating O3(I) phase wets high-angle grain boundaries in a manner analogous to grain boundary premelting, at least Δc=0.15 before the O3(II)-O3(I) equilibrium phase boundary, c=0.75. A critical misorientation as a function of the macroscopic lithium content, Δθc(c) exists above which the grain boundaries undergo a metal-insulating transition. The critical misorientation decreases with composition until at c=0.81, the percolation threshold is reached, forming an insulating grain boundary network that dramatically suppresses the electrical conductivity of polycrystalline LCO. The O3(I) phase extends into the O3(II) grain interiors through a diffusion-limited process, while the O3(II) phase extends into the H1-3 grain interiors through a phase transformation limited process. Results suggest that the fabrication of textured LCO microstructures will delay the metal–insulator transition. Specifically, textured microstructures exhibiting grain boundary misorientations Δθ<6∘ will suppress the formation of the insulating O3(I) phase up to the O3(II)-O3(I) phase boundary, enabling the use of an additional 64.6 Wh/kg in specific energy density and 16.4 Ah/kg of charge between c=0.75 and c=0.81.

Improving the mechanical properties of duplex Mg-Li-Zn alloy by mixed rolling processing

The microstructure and mechanical properties of a dual-phase Mg-9Li-1Zn (LZ91) alloy after 80% rolling at 250 °C and then additional 10% room temperature rolling are studied. After the rolling process, the Mg-rich phase (α phase) is squashed and stretched, and Li-rich phase (β phase) is refined. A large number of small ellipsoidal secondary Mg-rich phases are precipitated in β phase after rolling process. In addition, Zn-containing phases are precipitated surrounding α phase and in β phase. Under the combined precipitation strengthening of the secondary phases, fine-grain strengthening and processing strengthening in room temperature rolling, the strength of Mg-9Li-1Zn alloy is greatly enhanced. The tensile strength and yield strength of Mg-9Li-1Zn alloy reach 251 MPa and 233 MPa, respectively, and the elongation is over 20%.

Fundamental mechanism revealed for lithium deficiencies engineering in a new spherical Li-Rich Mn-based layered Li1.23Mn0.46Ni0.246Co0.046Al0.015O2 cathode

Here, a new spherical Li1.23Mn0.46Ni0.246Co0.046Al0.015O2 (0.6Li2MnO3•0.4LiNi0.8Co0.15Al0.05O2, LMNCA) cathode with low cobalt content is rationally designed and prepared. The lithium deficiencies engineering with different lithium (from 75% to 103% of theoretically stoichiometric ratio lithium) is conducted in LMNCA to enhance its electrochemical performance. For the first time, it is found that the Li-rich phase of Li2MnO3 decreases while the distorted spinel phase with low electrochemical kinetics is in-situ formed and increases with the gradual increase of the lithium deficiencies. However, the content of layered LiMO2 with the space group R3—m does not change. Proper amount of Lithium deficiencies and phase composition with appropriate phase ratios can make the LMNCA exhibit excellent electrochemical cycling stability, which shows the first cycle discharge specific capacity of 233 mAh g−1 with an initial Coulombic efficiency of 81% at C/10, and decays to 195 mAh g−1 over 200 cycles with the capacity retention of 90.6% under C/5 charge and C/3 discharge. However, excessive lithium deficiencies and phase composition with unbalanced phase ratios reduce the electrochemical performance of the LMNCA. The relationship between the lithium deficiencies, the crystalline component, and the electrochemical performance of the novel LMNCA is fundamental disclosed, which would shed light on the designing and synthesis of advanced Li-rich Mn-based layered oxide cathode with low or free cobalt content .