Cathode Materials For Li-ion Batteries Research Articles

Engineering robust biopolymer-derived carbon growth of Ni-rich cathode materials for high-performance Li-ion batteries

Nickel-rich ternary layered oxide (NCM811) is one of the most promising electrode materials for next-generation lithium ion batteries, offering high reversibility, ecofriendly, and low cost. However, this type of cathode material also has low thermal stability, phase changes during charge-discharge, and safety concerns, requiring considerable improvement to be commercially viable. This study induced carbon growth on a modified nickel-rich layered oxide NCM811 cathode material as positive electrodes for Li ion batteries, and subsequently performed electrochemical, structural, and post-mortem characterization for the material. Specific capacity retention for the best case cathodes improved to 75 % after 100 cycles at 0.1C rate under atmospheric conditions compared with current standard NCM electrodes. Full cell fabricated using that best case electrodes achieved 220 mAh g−1 initial charge capacity, retaining 81 % charge capacity after 50 cycles. Initial coulombic efficiency and cycle stability for the prepared best case cathode material was enhanced by optimum carbon growth due to the reconstructed layer structure's capacity to inhibit side reactions at the interface and stabilize bulk structure over cycles.

Multi-scale design of three-dimensional highly-conductive spherical Li-rich layered manganese oxide toward long-term stable cyclability

The improvement of the cyclability and voltage decay of Li-rich layered manganese oxides (LLMOs) is crucial for developing Li-rich-based high energy density Li-ion batteries. However, the electron/ion transport mismatch and constant corrosion induced by the electrolyte remain huge challenges. In this work, we design a 3D highly conductive spherical structure using COMSOL simulations and synthesize a lithium silicate and graphene cocoated LLMO with high tap density by using liquid polysiloxane as the silicon source. Their synergistic effects reduce the activation energy in the lithiation/delithiation process, decrease the polarization, improve the thermal stability, and hinder the dissolution of transition metal ions in the material, thereby enhancing the electrochemical performance of the composite. After 200 cycles, the discharge capacity of the cocoated material is 212.9 mAh g−1 (91.3% capacity retention), the discharge specific energy reaches 713.5 Wh kg−1, and the discharge middle voltage increases by 0.1 V relative to the pristine sample after 200 cycles. The 3D structural design and multiscale modifications described herein greatly facilitate the commercialization of lithium-rich layered manganese oxides as cathode materials for next-generation Li-ion batteries with high energy density.

Origin of high stability, enhanced specific capacity, and low Li diffusion energy in boron doped Li3V2(PO4)3

Li3V2(PO4)3 (LVP) is a well-known cathode material of Li-ion batteries, whereas the specific capacity is limited by the maximum Lithium (Li) de-intercalation probability associated with vacancy energy. The reason behind this limitation is not known yet, which needs to be address, and the modification needs to be done in the electronic structure to get a more specific capacity. In this work, using First-principles calculation, we have found that Li1 (the tetrahedra geometry) is having a higher Li vacancy energy as compared to Li2 and Li3, which limits the Li de-intercalation below x = 1.8, (where x is Li concentration). The change in bandgap of LVP structure after boron (B) substitution is directly correlated to the change in the oxygen (O) occupancy due to B substitution. As of comparing formation energy plot of pristine LVP and B substituted LVBP structure, we have found that in case of LVBP structure formation of x > 2 Li de-intercalation is possible, which help to enhance the specific capacity up to 205 mAh/g. Overall, we identify the cause of the less specific capacity of LVP and provide the solution by suggestion B doping, which also provides less Li diffusion barrier energy.

On the Origin of Ion Intercalation and Conductivity Enhancement in Sn-Doped V2O5 Cathodes of Li-Ion Batteries: A Computational Study

Vanadium pentoxide (V2O5) is one of the most promising cathode materials used in metal-ion batteries due to its high theoretical capacity. But it still suffers from low electronic conductivity leading to sluggish ion transport kinetics. Although the introduction of Sn impurities in V2O5 has been proposed to partially alleviate these drawbacks, the origin of the improvement is still unclear. In this work, we employed the density functional theory (DFT+U) method to study the role of Sn doping on the enhanced electronic conductivity and Li intercalation. Using a thermodynamic model based on defect formation energies and charge neutrality constraint, we find that Sn substitution at a vanadyl group (SnVO) is likely to occur upon Sn doping. The SnVO defect generates one electron polaron at the nearby V center, which could escape the defect site upon thermal excitation with a barrier of 0.55 eV. Such a relatively mobile polaron could act as a charge carrier and enhance the electronic conductivity of the cathode. Upon Li intercalation, the SnVO defect with a repulsive nature toward Li serves as a nucleation center, where Li could accumulate nearby the defect site. This could enhance the formation of a lithiated phase during the early discharge process. However, loading too much Sn could lead to inferior cathode performance since it impedes Li diffusion. Our findings provide insights into the role of Sn doping in the design of high-performance V2O5-based cathode materials for Li-ion batteries.

Vinyltrimethylsilane as a novel electrolyte additive for improving interfacial stability of Li-rich cathode working in high voltage

Boosting the interfacial stability between electrolyte and Li-rich cathode material at high operating voltage is vital important to enhance the cycling stability of Li-rich cathode materials for high-performance Li-ion batteries. In this work, vinyltrimethylsilane as a new type of organic silicon electrolyte additive is studied to address the interfacial instability of Li-rich cathode material at high operating voltage. The cells using vinyltrimethylsilane additive shows the high capacity retention of 73.9% after 300 cycles at 1 C, whereas the cells without this kind of additive only have the capacity retention of 58.9%. The improvement of stability is mainly attributed to the additive helping to form a more stable surface film for Li-rich cathode material, thus avoiding direct contact between the electrolyte and the cathode material, slowing down the dissolution of metal ions and the decomposition of the electrolyte under high operating voltage. Our findings in this work shed some light on the design of stable cycling performance of Li-rich cathode toward advanced Li-ion batteries.

An ab initio investigation of LiCoBO3 as Li-ion battery cathode material

We give a first principles approach for the structural, electronic and magnetic properties of LiCoBO3 and CoBO3 in the monoclinic lattices. Along [001] direction, based on density functional theory approach and using Full Potential Linear Augmented Plane Wave (FP-LAPW) method, Polarized spin and spin–orbit coupling are included in calculations, and major spin was set up. The calculations were carried out using generalized gradient approximation (GGA) + an on-site Coulomb self-interaction correction potential (GGA + U). The magnetic and orbital moments are estimated. The U value was considered to be equal to 6 eV for Co atom. The average equilibrium voltage over a full cycle, of the LiCoBO3 battery is estimated from our FP-LAPW calculations. The capacity of a cell and energy density of LiCoBO3 were calculated. The compound LiCoBO3 is a semiconductor with average intercalation voltage 4.01 V. The voltage difference help promote electrochemical performance, which opens a window for Li-ion battery marketing application.

Multiscale strain alleviation of Ni-rich cathode guided by in situ environmental transmission electron microscopy during the solid-state synthesis

Ni-rich layered oxides are one of the most promising cathode materials for Li-ion batteries due to their high energy density. However, the chemomechanical breakdown and capacity degradation associated with the anisotropic lattice evolution during lithiation/delithiation hinders its practical application. Herein, by utilizing the in situ environmental transmission electron microscopy (ETEM), we provide a real time nanoscale characterization of high temperature solid-state synthesis of LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode, and unprecedentedly reveal the strain/stress formation and morphological evolution mechanism of primary/secondary particles, as well as their influence on electrochemical performance. We show that stress inhomogeneity during solid-state synthesis will lead to both primary/secondary particle pulverization and new grain boundary initiation, which are detrimental to cathode cycling stability and rate performance. Aiming to alleviate this multiscale strain during solid-state synthesis, we introduced a calcination scheme that effectively relieves the stress during the synthesis, thus mitigating the primary/secondary particle crack and the detrimental grain boundaries formation, which in turn improves the cathode structural integrity and Li-ion transport kinetics for long-life and high-rate electrochemical performance. This work remarkably advances the fundamental understanding on mechanochemical properties of transition metal oxide cathode with solid-state synthesis and provides a unified guide for optimization the Ni-rich oxide cathode.

Porous anhydrous CuF2 with a micro-nano-hierarchical structure as high-performance cathode material for Li-ion battery

Porous anhydrous CuF2 with a micro-nano-hierarchical structure as high-performance cathode material for Li-ion battery

Conflicting roles of F doping on electrochemical performance of layered-spinel Li1.2Mn0.75Ni0.25O2-zFz as cathode materials for Li-ion batteries

Herein, the conflicting roles of F doping on the electrochemical performance of layered-spinel Li1.2Mn0.75Ni0.25O2-zFz (z = 0, 0.05, 0.1) cathode materials are studied. The compound consists of Li1.2Mn0.6Ni0.2O2 and LiMn1.5Ni0.5O4 with their phase ratio depending on F doping content. When z = 0.05, it favors the spinel phase formation, leading to increased first Coulombic efficiency and improved cycle stability. However, it reduces the cathode capacity to 250 mAh g−1 at C/10 (the capacity of the pristine is 280 mAhg−1). With F doping content increasing to z = 0.1, the cycle stability of the cathode is the best, with 96 % capacity retention after 200 cycles at C/2. The high level of F stabilizes the structure, prevents phase transition, and retards voltage decay. The result demonstrates a promising strategy for the design of composite cathode materials by F doping.

Surface protection of NMC811 cathode material via ZnSnO3 perovskite film for enhanced electrochemical performance in rechargeable Li-ion batteries

In order to achieve the maximum utilization of Ni-rich cathode materials in the next generation Li-ion batteries, a new perovskite-type ZnSnO3 (ZTO) film was prepared on the surface of LiNi0.8Mn0.1Co0.1O2 particles via an in-situ co-precipitation method at a low annealing temperature. The changes in the crystallographic and functional properties were investigated via XRD and FTIR instruments. The formation of the core-shell structure was confirmed through surface inspection techniques such as FESEM/EDS and XPS. Fitting of O 1s spectra revealed more oxygen vacancies on the surface of ZTO@NMC811 than pristine NMC811 sample. The electrochemical cycling tests revealed that ZnSnO3-coated NMC811 delivered the highest charge and discharge capacities of about 223 and 202 mAhg−1 after first cycle. Furthermore, the surface modified NMC811 showed higher rate capability performance, maintaining about 73% of its initial capacity after re-cycling at 0.1C between cycle no. 25 and 30. The enhanced electronic and ionic conduction after ZnSnO3 film coating was certified by the significant decrease in Ohmic (Rs) and charge transfer (Rct) resistances before and after cycling. The improved cyclability and reversibility could be attributed to the protective role of the ZnSnO3 layer in preserving the layered crystal structure by suppressing side reactions between the active materials and electrolyte.

Hydrogen Reduction of LiCoO2 Cathode Material: Thermodynamic Analysis, Microstructure, and Mechanisms

Hydrogen is an alternative reductant to replace carbon for the production of metals. Reduction by hydrogen has advantages compared to carbothermic reduction, such as faster reaction rate and cleaner by-product (water vapor). This study investigated the application of hydrogen reduction for recycling and recovering cobalt and lithium from Li-ion battery cathode material (LiCoO2). The study consisted of thermodynamic simulations of the reactions and microstructure evolution analysis from experimental work to propose mechanisms of the reduction process. The thermodynamic assessment predicted that metallic Co could be generated from 400 °C and was stable up to 1200 °C, but strongly dependent on the molar amount of H2. The final experimental reduction products of lithium and cobalt were found to vary and consisted of Li2O, LiOH, Li2O2 and Co, CoO, Co3O4, respectively. The experimental work revealed that the overall reduction mechanism is uniquely characterized by the reduction temperature. The temperature range of 800 °C to 900 °C offered more benefit as Co could be generated as a larger mass indicating a more progressive reduction. The data and information obtained can help optimize the parameters in the recycling of Li-ion batteries.

Effect of the PrPO4 modification on the structure and electrochemical performance of LiCoO2

Increasing interest in LiCoO2 as a cathode material for Li-ion batteries has recently arisen due to its high operating voltage, high energy density and long cycle life. However, irreversible structural damage and severe side reactions at high cut-off voltages severely deteriorate the electrochemical performance of LiCoO2 materials, resulting in a series of safety issues when used in batteries. In this work, PrPO4, Li2CO3 and Co3O4 are mixed and then treated at a high temperature to obtain PrPO4-modified LiCoO2 with improved electrochemical performance at 4.55 V. XRD and Rietveld refinement results confirm that the modified LiCoO2 materials exhibit well-ordered structures with compact unit cells. PrPO4 is not incorporated into the crystal lattice of LiCoO2 but converted by Li2O and Co3O4 into PrCoO3 and Li3PO4 phases during the reaction. Additionally, these two phases are well-incorporated into the LiCoO2 particle. Electrochemical tests indicate that the irreversible capacity during cycling is significantly reduced by PrPO4 modification. Benefiting from the enhanced interface stability induced by Li3PO4 and PrCoO3, the 1 mol% PrPO4-modified LiCoO2 sample exhibits an initial discharge capacity of 185 mAhg−1 at 0.5C with a capacity retention of 92.4% after 100 cycles, as well as an excellent rate capability with a capacity of 128 mAhg−1 even at 5C.

Chemical lithiation methodology enabled Prussian blue as a Li-rich cathode material for secondary Li-ion batteries

Prussian blue analogues (PBAs) have been attracting intense attention owing to its two-electron storage capability and considerable cost advantage, especially in Na-ion and K-ion batteries. However, things are quite different when it comes to Li-ion batteries, because lithium-containing Li4Fe(CN)6 precursor is not commercially available and thus the traditionally prepared Li-deficient FeFe(CN)6 products fail to couple with commercial graphite anode for full cells. Herein, we put forward a potential matching principle to guide the chemical pre-lithiation of FeFe(CN)6 into a Li-rich LixFeFe(CN)6 (x varies from 0 to 2) cathode. The potential matching principle was convincingly confirmed by theoretical analysis and over-lithiation experiments. Perylene-Li reagent was elaborately screened to serve as both Li+ and electron donor for controllable chemical lithiation reaction while preserving the host framework stable. Our work provided a general guiding principle and effective methodology for controllable synthesis of Prussian blue analogues in gradient lithiation depth, which could be served as a platform for in-depth, systematic and comprehensive research on the properties of PBAs materials.

Direct Solution-calcination synthesis of residual Li-free layered cathode materials for Li-ion batteries

Layered cathode materials have advanced existing Li-ion batteries by improving cell voltage and enabling facile charge transfer. Yet diverse synthetic issues such as particle inhomogeneity, Li residues, complicated processes, and large micron-scale particle sizes, need to be addressed. We report a direct solution-calcination strategy for the simple and scalable synthesis of layered cathode materials (i.e. LiCoO2) for Li-ion batteries. Polyvinylpyrrolidone (PVP) as functional agent is introduced to intimately bind and uniformize the metal precursors, thereby sufficiently eliminating surface Li residues and forming a uniform particle distribution. Compared with commercial LCO, solution-calcined LCO exhibits improved cycling stability and rate capability with suppressed phase transition. The structural phase evolution mechanism for solution-calcination is investigated using in-situ X-ray diffraction analysis. Overall, our research suggests a simple and versatile strategy for the synthesis of cathode materials; the proposed method is effective and avoids complicated synthesis steps and the formation of unwanted residual lithium compounds.

Design and construction of Prussian blue analogue combined by Na2WO4 toward high-performance cathode materials for Li-ion battery

Prussian blue analogues have been considered as one of hopeful cathode materials of Li-ion batteries (LIBs) because of their tunable composition, low cost and simple synthesis method, but the high volume variation and electrical resistance during cycling limit the wide application. In this work, Na1.06Fe[Fe(CN)6]·2.8H2O/Na2WO4 (PBA/NW) composites with high performance are successfully synthesized by a hydrothermal route following through a simple solution dispersion approach. The Na2WO4 coating will not alter the structure and morphology of PBA sample. Na2WO4 coating improves the structure stability and Li+ insertion/extraction reversibility, and decreases the charge transfer resistance, then promotes the transfer of Li+. The PBA-NW2 indicates an outstanding reversible discharge capacity of 134.9 mAh g−1 at 1C after 1000 cycles, but the pure PBA only performs a discharge capacity of 108 mAh g−1. In addition, PBA-NW2 also indicates superior rate property with discharge capacity of 150.3, 145.1, 140.0, 132.5, 132.32, 105.3, 91.9 mAh g−1 at 0.1, 0.3, 0.5, 1, 2, 5 and 10C, respectively. This work offers a facile and easy synthesis method to construct high-performance Prussian blue analogues cathode material for low-cost LIBs.

Black Phosphorus/V3C2 MXene Layered Heterostructure as a Sustainable Cathode Material for Li-Ion Battery: An Ab Initio Study

Layered heterostructures have been recognized as next generation cathode materials for ion batteries owing to their high mobility and ion loading capability. Herein, we report black phosphorus (BP)/MXene layered heterostructures (BP/V3C2, BP/V3C2N2, BP/V3C2O2, and BP/V3C2Cl2) and their computational investigation for Li-ion battery. First-principles calculations have been carried out for Li ion intercalation followed by computing open-circuit voltage (ranges from 1.08 to 2.17 V for BP/V3C2, 3.78 to 1.79 V for BP/V3C2N2, 2.97 to 2.04 V for BP/V3C2O2, and 1.84 to 2.12 V for BP/V3C2Cl2), adsorption energy (−1.87 eV per Li atom for BP/V3C2, −2.49 eV per Li-atom for BP/V3C2N2, −2.25 eV per Li atom for BP/V3C2O2, and −1.92 eV per Li-atom for BP/V3C2Cl2), and diffusion barrier. Notably, the optimized BP/V3C2 layered heterostructure exhibits 630.320 mAh g–1 Li storage capacity which is significantly higher than the earlier reported 2D cathode materials. Our simulated results indicate that BP/V3C2, BP/V3C2N2, BP/V3C2O2, and BP/V3C2Cl2 layered heterostructures can be considered as favorable cathode materials for sustainable Li-ion batteries.

Predicting the Lithium-Vacancy Arrangements of Layered Cathode Materials by a Voronoi Finite Element Method

We proposed a Voronoi finite element (VFE) method to determine the possible intermediate phases of cathode materials of Li-ion batteries (LIBs). Lithium-vacancy arrangements can be accurately predicted based on Voronoi polyhedra centered on lithium ions. Using this method, we can reproduce the well-known lithium removal processes of LiCoO2 and Li1.2Mn0.54Ni0.13Co0.13O2. Moreover, this method can effectively reduce the number of arrangements that need to be calculated. Our work provides a reasonable and efficient way to investigate the structural evolution of cathode materials during delithiation.

Acid- and Gas-Scavenging Electrolyte Additive Improving the Electrochemical Reversibility of Ni-Rich Cathodes in Li-Ion Batteries.

In view of their high theoretical capacities, nickel-rich layered oxides are promising cathode materials for high-energy Li-ion batteries. However, the practical applications of these oxides are hindered by transition metal dissolution, microcracking, and gas/reactive compound formation due to the undesired reactions of residual lithium species. Herein, we show that the interfacial degradation of the LiNi0.9CoxMnyAlzO2 (NCMA, x + y + z = 0.1) cathode and the graphite (Gr) anode of a representative Li-ion battery by HF can be hindered by supplementing the electrolyte with tert-butyldimethylsilyl glycidyl ether (tBS-GE). The silyl ether moiety of tBS-GE scavenges HF and PF5, thus stabilizing the interfacial layers on both electrodes, while the epoxide moiety reacts with CO2 released by the parasitic reaction between HF and Li2CO3 on the NCMA surface to afford cyclic carbonates and thus suppresses battery swelling. NCMA/Gr full cells fabricated by supplementing the baseline electrolyte with 0.1 wt % tBS-GE feature an increased capacity retention of 85.5% and deliver a high discharge capacity of 162.9 mAh/g after 500 cycles at 1 C and 25 °C. Thus, our results reveal that the molecular aspect-based design of electrolyte additives can be efficiently used to eliminate reactive species and gas components from Li-ion batteries and increase their performance.

Synthesis of LiCoO2 cathode materials for Li-ion batteries at low temperatures

It is costly to synthesize cathode materials through the solid reaction of raw materials at relatively high temperatures due to its high energy consumption. Here, we use LiCoO2 as a model material to demonstrate a novel method for synthesizing cathode materials within 120 s at temperatures as low as 260 °C under an AC electric field. The influence of the current density, current retention time, and synthesis atmosphere on the prepared LiCoO2 materials was systematically investigated. The results indicate that the acceleration of the synthesis process between Co2O3 and Li2CO3 is due to the introduction of oxygen vacancies into the reaction system under a threshold electric field. The obtained LiCoO2 exhibits the same electrochemical performance as that of LiCoO2 synthesized via the conventional thermal reaction method. The proposed synthesis method could provide a cost-effective pathway to synthesize different cathode materials.

Insights into the Structural and Thermodynamic Instability of Ni-Rich NMC Cathode

The Ni-rich LiNi1-x-yMnxCoyO2 (NMC) layered oxides have been promising materials to replace the LiCoO2 commercial cathode due to their high operation voltages, low cost, and enhanced capacity. However, structural instability is the main drawback of the Ni-rich NMC system, leading to capacity fading, which prevents its commerce application. While numerous efforts have been made to comprehend and overcome this issue, there remains a lack of systematic phase stability analysis which is an essential factor to be addressed. Herein, systematic first-principles calculations were performed in this study to reveal the structural, oxidation, and phase stability of Ni-rich NMC during delithiation. This is the first report on competing phases of Ni-rich NMC at various states of charge (SoCs). The compounds with the spinel and rock salt structures formed during delithiation and oxygen evolution takes place at highly delithiation cases, which are likely the origins of capacity fading and crack formation at the surface. This work also outlined the thermodynamic foundation of doping and oxidation state gradient-based core–shell strategies for resolving the instability and enhancing the capacity retention of Ni-rich NMC layered oxides as cathode materials in Li-ion batteries.