Li-ion Battery Cathode Research Articles

On Proton Defects and the Phase Transformation of NiO2

One approach to high-capacity Li-ion battery cathodes is to increase the Ni content. Unfortunately, Ni-rich materials undergo a phase transition and volume collapse at a high state of charge (SOC), which degrades battery performance. At a high SOC, NiO2 undergoes a phase transition from the O3 to the O1 phase. The O1 phase appears to be more thermodynamically stable than the O3 phase. However, density functional theory (DFT) often predicts higher stability for O3, depending on the DFT approximation. The energy difference between the O1 and O3 phases is on the order of 10 meV/atom. We find that proton defects are more stable in the O1 phase than in the O3 phase by about 90 meV per proton. Defects in NiO2 energetically favor the O3–O1 phase transition observed in a high SOC in LixNiO2.

Influence of nano-fibrous and nano-particulate morphology on the rate capability of Li3V2(PO4)3/C Li-ion battery cathode

We demonstrate contrasting differences in the electrochemical performances of Li3V2(PO4)3 with thin-carbon coating (LVP/C) in the nanoparticulate (LVP/C-np) and nanofibrous (LVP/C-nf) morphologies synthesized by a sol-gel and electrospinning processes, respectively. LVP/C-nf exhibits a highly-interconnected pearl-like microstructure, and LVP/C-np has discontinuous aggregates of nanoparticles, as evidenced by high-resolution scanning and transmission electron microscopy. Electrochemical studies show that the nanoparticle cathodes exhibit higher capacity fading than nanofibrous cathodes with increasing C-rate. LVP/C-np and LVP/C-nf cathodes exhibit a discharge capacity of 137 mA h g−1 and 124 mA h g−1 at 0.1 C rate. Large carbon content in LVP/C-nf (∼23.3%) unlike the LVP/C-np (∼2.5%) underestimates the actual capacity. The high C-rate performance is better for LVP/C-nf (58.74 mA h g−1 at 10C-rate and 28.75 mA h g−1 at 30 C-rate) compared to LVP/C-np (37.23 mA h g−1 at 10C-rate) as tested in the voltage range 3 V-4.8 V. The most prominent observation is that LVP/C-np cathodes show lower capacity retention of only 48.6%. In contrast, the cathodes with nanofibrous morphology retain nearly 77.2% of their initial discharge capacities after 500 cycles at 1C-rate. Present study highlights the importance of the well-connected microstructure of the cathode as an essential criterion to achieve the high-rate capability and long cycling stability of high voltage cathodes for quick charge battery applications.

Electrochemical phase transition of LixCoO2 from machine-learning-based global optimization

Li-ion battery cathodes undergo significant structure transition under (dis)charging conditions, which in turn significantly affects its electrochemical performance. This complex phenomenon raises continuous interests in both science and industry for understanding the structure–activity dynamics under (de)lithiation conditions. Here we report the first theoretical attempt, by combining the machine-learning-based global optimization (SSW-NN method) and first-principles calculations, to elucidate the Li-dependent structure evolution and the Li diffusion barrier of LixCoO2 cathode under (de)lithiation conditions. The thermodynamic and kinetics of the LixCoO2 proposed in this work provides new insight for designing the next generation of high stability electrode materials in Li-ion batteries.

Synthesis and electrochemical performance of La2CuO4 as a promising coating material for high voltage Li-rich layered oxide cathodes

The structural transformations, oxygen releasing and side reactions with electrolytes on the surface are considered as the main causes of the performance degradation of Li-rich layered oxides (LROs) cathodes in Li-ion batteries. Thus, stabilizing the surfaces of LROs is the key to realize their practical application in high energy density Li-ion batteries. Surface coating is regarded as one of the most effective strategies for high voltage cathodes. The ideal coating materials should prevent cathodes from electrolyte corrosion and possess both electronic and Li-ionic conductivities simultaneously. However, commonly reported coating materials are unable to balance these functions well. Herein, a new type of coating material, La2CuO4 was introduced to mitigate the surface issues of LROs for the first time, due to its superb electronic conductivity (26–35 mS⋅cm−1) and lithium-ionic diffusion coefficient (10−12–10−13 cm2⋅s−1). After coating with the La2CuO4, the capacity retention of Li1.2Ni0.54Co0.13Mn0.13O2 cathode was increased to 85.9% (compared to 79.3% of uncoated cathode) after 150 cycles in the voltage range of 2.0–4.8 V. In addition, only negligible degradations on the deliverable capacity and rate capability were observed.

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.

CePO4/Spinel dual encapsulating on Li-rich Mn-based cathode with novel cycling stability

Li-rich Mn-based cathode materials (LMR) are promising cathodes for next-generation Li-ion batteries due to their high specific capacities, while the surface irreversible redox reactions lead to persistent capacity and voltage fading severely limit their commercial applications. We generated the CePO4/Spinel dual encapsulated modified layer in situ on the surface, with spinel phase derived in the sub-outer layers of the layered crystal, forming a good transition structure at the interface of the two phases. The surface phosphate coating enhances the protection of the original structure, which not only effectively stabilizes the evolution of lattice oxygen, but also suppresses interfacial side reactions and transition metals dissolution. The spinel phase formed on the subsurface can provide fast Li+ migration channels due to its unique three-dimensional structure, which can greatly overcome the Li+ diffusion barrier and strengthen the Li+ diffusion kinetics of the electrode material. This integrated modification strategy can significantly improve the initial coulombic efficiency (ICE), rate performances and cycling stability of the material. The ICE of LMNF-2 increased from 78.36% to 85.88%, and the first discharge specific capacity reached 257.33 mAh g−1 at 0.1 C, the capacity retention was 76.43% with only 0.15 V voltage decay after 300 cycles at 1 C. The lithium-ion full cell employing LMNF-2 and graphite exhibit a specific energy density of 450 Wh kg−1 at 0.1 C, and shows an optimum cycling stability with capacity retention of 87.2% for 100 cycles at 1 C.

Stacking Faults Inducing Oxygen Anion Activities in Li2 MnO3.

Controllable anionic redox for a transformational increase in the energy density is the pursuit of next generation Li-ion battery cathode materials. Its activation mechanism is coupled with the local coordination environment around O, which posts experimental challenges for control. Here, the tuning capability of anionic redox is shown by varying O local environment via experimentally controlling the density of stacking faults in Li2 MnO3 , the parent compound of Li-rich oxides. By combining computational analysis and spectroscopic study, it is quantitatively revealed that more stacking faults can trigger smaller LiOLi bond angles and larger LiO bond distance in local Li-rich environments and subsequently activate oxygen redox reactivity, which in turn enhances the reactivity of Mn upon the following reduction process. This study highlights the critical role of local structure environment in tuning the anionic reactivity, which provides guidance in designing high-capacity layered cathodes by appropriately adjusting stacking faults.

Study of polyethylene coating to improve the cycle stability of Ni-rich cathode for Li-ion batteries

Study of polyethylene coating to improve the cycle stability of Ni-rich cathode for Li-ion batteries

Architecting “Li-rich Ni-rich” core-shell layered cathodes for high-energy Li-ion batteries

Li-rich or Ni-rich layered oxides are considered ideal cathode materials for high-energy Li-ion batteries (LIBs) owing to their high capacity (> 200 mAh g–1) and low cost. However, both are suffering from severe structural instability upon high-voltage cycling (> 4.5 V). Here, “Li-rich Ni-rich” Li1.08Ni0.9Mn0.1O2 oxides with core-shell architecture are designed and synthesized to improve their high-voltage cyclability. These oxides are determined to be composed of a less reactive “Li-rich Mn-rich” shell and a high-capacity “Li-rich Ni-rich” core. As Li-ions gradually enter into the core-shell precursor during high-temperature lithiation reaction, the interdiffusion of elements across the interphase between the Mn-rich shell and the Ni-rich core successively occurs. Such thermally-driven atomic interdiffusion could lead to a thickness-controllable “Li-rich Mn-rich” shell, which can guarantee an exceptional structural reversibility for the layered “Li-rich Ni-rich” core upon long-term cycling. As a consequence, the optimized core-shell Li1.08Ni0.9Mn0.1O2 achieves a capacity retention of 96% at 0.1 C after 100 cycles in the voltage range of 2.7–4.6 V. These findings might open up a new avenue for rational design of advanced cathode materials for LIBs and beyond.

Tc doping in V$$_{2}$$O$$_{5}$$ as an Li-ion battery cathode to enhance the electrochemical performance: A first-principles study

Tc doping in V$$_{2}$$O$$_{5}$$ as an Li-ion battery cathode to enhance the electrochemical performance: A first-principles study

Molten-chlorides assisted rapid preparation and crystallinity-irrelevant properties of nanostructured LiCoO2 as lithium-ion battery cathodes

In this paper, the 850 °C molten-chlorides (NaCl-KCl, eutectic point ∼657 °C) assisted reaction of Co3O4 (melting point ∼895 °C) with LiOH⋅H2O (melting point ∼462 °C) is adopted for the precursor shape-replicated construction of nanostructured LiCoO2, focusing on the rapid formation mechanism and crystallization-irrelevant properties of phase-pure LiCoO2 for Li-ion battery (LIB) cathodes. Temperature−/time-dependent crystallization shows that, after the heterogeneous nucleation of LiCoO2 at 660 °C, the complete consumption of Co3O4 occurs at 850 °C within 10 min and the building block of each of the finally resulting 850 °C/8-h LiCoO2 microspheres has been endowed with a (003)-manifest crystal plane. By comparison, it is due to the complete consumption of Li-insulating Co3O4, not to the increase of LiCoO2 crystallinity, that explains the high electrochemical properties of these phase-pure samples. Especially, cycling stabilities of the 850 °C/10-min and 850 °C/8-h LiCoO2 are close to each other, but each of them is much better than those of the chlorides-absent counterparts obtained at the node of 850 °C/8-h. These, together with the approximate rate capabilities of these chlorides-present LiCoO2, implies an applicable approach of the molten-salt method to the rapid construction of nanostructured LiCoO2 for high-performance LIB cathodes.

One-pot K+ and PO43− co-doping enhances electrochemical performance of Li-rich Li1.2Ni0.13Co0.13Mn0.54O2 cathode for Li-ion battery

The high specific capacity and voltage of Li-rich Mn-based oxides make them promising cathode materials for high-energy-density lithium-ion batteries (LIBs). However, the problems such as low initial coulombic efficiency, fast capacity and voltage fading, poor kinetics, large voltage hysteresis, and poor safety performance hamper their fast commercialization. Herein, we report one-pot K+ and PO43− co-doping Li-rich Mn-based oxides Li1.2Ni0.13Co0.13Mn0.54O2 cathode material to improve the electrochemical performance of the lithium-ion battery. On the one hand, K+ doping can stabilize the bulk structure and enlarge the Li slabs to facilitate the diffusion of Li+, resulting in enhanced cycling and rate performance. On the other hand, PO43− doping changes the electronic structure of the material and weakens the covalency of TM-O, decreasing the irreversible loss of lattice oxygen and stabilizing the structure. As a result, the K+ and PO43− co-doping can effectively alleviate the capacity and voltage decay and the modified sample shows better cycling stability (88.6%@0.5 C@250 cycles) and rate performance (155.5 mAh g −1@5 C) compared to the pristine material. Our strategy here provides a facile one-pot method to modify Li-rich Mn-based oxides cathode material for high-performance LIBs.

Green and sustainable recycling of MnCo2O4/Mn3O4/Li(Mn0.75Ni0.25)2O4 mixed oxide from of spent Li-ion and Zn–MnO2 batteries and evaluation of its photocatalytic properties

In this study, MnCo2O4/Mn3O4/Li(Mn0.75Ni0.25)2O4 spinel-like mixed oxide was synthesized by green recycling of spent Li-ion and Zn–MnO2 batteries. The first step consisted of leaching the cathode of Li-ion batteries and the cathode of Zn–MnO2 batteries with citric acid and glucose. Then, Li-ion cathode leachate was mixed with Zn–MnO2 cathode leachate. Leachate mixture received the addition of oxalic acid, yielding oxalate precursor material, which was calcined at 450 °C for 3 h to afford MnCo2O4/Mn3O4/Li(Mn0.75Ni0.25)2O4. Mixed oxide structure, composition, and morphology were determined by X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP OES), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photocatalytic properties of mixed oxide were evaluated in the decolorization of a model dye (methylene blue) under UV radiation. System using UV radiation + H2O2 + catalyst reached decolorization efficiency >93% in 120 min of reaction. This study provides a possible solution for two environmental liabilities (batteries and wastewater), and the results reported here are of scientific, economic, environmental, and social interest.

One-Step Calcination Synthesis of Bulk-Doped Surface-Modified Ni-Rich Cathodes with Superlattice for Long-Cycling Li-Ion Batteries.

Nickel-rich (Ni≥90 %) layered cathodes are critical materials for achieving higher-energy-density and lower-cost next-generation Li-ion batteries (LIBs). However, their bulk and interface structural instabilities significantly impair their electrochemical performance, thus hindering their widespread adoption in commercial LIBs. Exploiting Ti and Mo diffusion chemistry, we report one-step calcination to synthesize bulk-to-surface modified LiNi0.9 Co0.09 Mo0.01 O2 (NCMo90) featuring a 5 nm Li2 TiO3 coating on the surface, a Mo-rich Li+ /Ni2+ superlattice at the sub-surface, and Ti-doping in the bulk. Such a multi-functional structure effectively maintains its structural integrity upon cycling. As a result, such NCMo90 exhibits a high initial capacity of 221 mAh g-1 at 0.1 C, excellent rate performance (184 mAh g-1 at 5 C), and high capacity retention of 94.0 % after 500 cycles. This work opens a new avenue to developing industry-applicable Ni-rich cathodes for next-generation LIBs.

Degradation in Ni-Rich LiNi1–x–yMnxCoyO2/Graphite Batteries: Impact of Charge Voltage and Ni Content

Ni-rich LiNi1–x–yMnxCoyO2 (NMC) materials are attractive as cathodes for Li-ion batteries due to their high energy density and low Co content. However, these materials may display poor electrochemical reversibility relating to structural and interfacial instabilities. The influence of Ni content and level of delithiation during charge on degradation mechanisms and relevance to electrochemical cycling behavior are probed for LiNi0.6Mn0.2Co0.2O2 (NMC622) and LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode materials in a full cell configuration under two upper voltage limits (4.1 and 4.3 V). The combined use of dQ/dV analysis of electrochemical voltage profiles, operando XRD, and postcycling scanning electron microscopy (SEM) measurements indicates that a major contributor to capacity fade is the large anisotropic volume change from an H2 ⇄ H3 phase transition and associated mechanical degradation particularly for NMC811. Notably, transition metal dissolution and deposition on the negative electrode are found to correlate with the structural changes occurring in the cathode under high voltage charge. X-ray photoelectron spectroscopy (XPS) analyses of the cycled cathodes reveal a more organic-rich cathode–electrolyte interphase (CEI) when cycling to 4.3 V with lower relative amounts of LiF. Surface reconstruction is not a significant factor under these cycling conditions as determined by soft X-ray absorption spectroscopy (sXAS) analysis. The results emphasize the opportunity to match the electrochemical test parameters with the specific NMC active material to mitigate degradation and extend cycle life.

Elucidating degradation mechanisms of Co-free high-Ni layered oxide cathodes for Li-ion batteries via advanced X-ray-based characterization methods

High-Ni layered oxide cathodes without Co are being investigated as potential cathode materials for Li-ion batteries with high energy density. By decreasing the Co content, these cathodes not only boost energy density but also alleviate concerns about the supply instability and fluctuating cost of Co raw materials. However, the elevated Ni content in the layered oxides causes distinct chemo-mechanical degradation mechanisms that inhibit their commercial application. In order to gain insight into the degradation process at various scales, from the atomic to the particle and the electrode levels, and to devise ways to prevent degradation, multi-scale characterization methods are essential. In this review, we critically evaluate the role of Co substitution in high-Ni layered oxides and the impact of Co content on the chemo-mechanical degradation process. Furthermore, the use of advanced X-ray-based characterization methods, which have helped shed light on the degradation mechanisms of high-Ni cathodes, is also discussed.

Selenium-Doped Sulfurized Poly(acrylonitrile) Composites as Ultrastable and High-Volumetric-Capacity Cathodes for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries, despite their superior gravimetric energy density, are inferior to lithium-ion (Li-ion) batteries in terms of volumetric energy density because of the intrinsic low density of sulfur and the lightweight carbon host. Here, a new strategy is proposed to improve the volumetric capacity of sulfur cathode with selenium-doped sulfurized poly(acrylonitrile) (SPAN) as the electrode material. The introduction of Se not only accelerates the redox kinetics of sulfur conversion but also leads to dramatically enhanced active materials content and higher tap density of the electrode material. Consequently, the Se0.4SPAN composite delivers an impressive volumetric capacity of 1185 mAh cm–3 at 0.1 C, a high rate capability of 850 mAh cm–3 at 4 C, and excellent long-term stability over 500 cycles at 1 C. Self-discharge behavior and the shuttle effect are completely avoided due to the absence of soluble intermediates. Moreover, a remarkable volumetric energy density of 1537 Wh Lcathode–1 is achieved based on the densification effect with a high cathode density (1.51 g cm–3), which is comparable to the metal oxide cathode of Li-ion batteries. This study demonstrates a promising way to overcome the bottlenecks of current Li–S technologies for high volumetric-energy-density rechargeable batteries.

Electrolytes, Additives and Binders for NMC Cathodes in Li-Ion Batteries—A Review

Among the current battery technologies, lithium-ion batteries (LIBs) are essential in shaping future energy landscapes in stationary storage and e-mobility. Among all components, choosing active cathode material (CAM) limits a cell’s available energy density (Wh kg−1), and the CAM selection becomes critical. Layered Lithium transition metal oxides, primarily, LiNixMnyCozO2 (NMC) (x + y + z = 1), represent a prominent class of cathode materials for LIBs due to their high energy density and capacity. The battery performance metrics of NMC cathodes vary according to the different ratios of transition metals in the CAM. The non-electrode factors and their effect on the cathode performance of a lithium-ion battery are as significant in a commercial sense. These factors can affect the capacity, cycle lifetime, thermal safety, and rate performance of the NMC battery. Additionally, polycrystalline NMC comprises secondary clusters of primary crystalline particles prone to pulverization along the grain boundaries, which leads to microcrack formation and unwanted side reactions with the electrolyte. Single-crystal NMC (SC-NMC) morphology tackles the cycling stability issue for improved performance but falls short in enhancing capacity and rate capability. The compatibility of different combinations of electrolytes and additives for SC-NMC is discussed, considering the commercial aspects of NMC in electric vehicles. The review has targeted the recent development of non-aqueous electrolyte systems with various additives and aqueous and non-aqueous binders for NMC-based LIBs to stress their importance in the battery chemistry of NMC.

Leaching kinetics of fluorine during the aluminum removal from spent Li-ion battery cathode materials

The high content of aluminum (Al) impurity in the recycled cathode powder seriously affects the extraction efficiency of Nickel, Cobalt, Manganese, and Lithium resources and the actual commercial value of recycled materials, so Al removal is crucially important to conform to the industrial standard of spent Li-ion battery cathode materials. In this work, we systematically investigated the leaching process and optimum conditions associated with Al removal from the cathode powder materials collected in a wet cathode-powder peeling and recycling production line of spent Li-ion batteries (LIBs). Moreover, we specifically studied the leaching of fluorine (F) synergistically happened along with the removal process of Al, which was not concerned about in other studies, but one of the key factors affecting pollution prevention in the recovery process. The mechanism of the whole process including the leaching of Al and F from the cathode powder was indicated by using NMR, FTIR, and XPS, and a defluoridation process was preliminarily investigated in this study. The leaching kinetics of Al could be successfully described by the shrinking core model, controlled by the diffusion process and the activation energy was 11.14 kJ/mol. While, the leaching of F was attributed to the dissolution of LiPF6 and decomposition of PVDF, and the kinetics associated was described by Avrami model. The interaction of Al and F is advantageous to realize the defluoridation to some degree. It is expected that our investigation will provide theoretical support for the large-scale recycling of spent LIBs.

Reciprocal irreversibility compensation of LiNi0.2Co0.2Al0.1Mn0.45O2 cathode and silicon oxide anode in new Li-ion battery

A layered LiNi0.2Co0.2Al0.1Mn0.45O2 cathode is herein synthetized and investigated. Scanning electron microscopy (SEM) shows the layered morphology of the composite powder, while energy dispersive X-ray spectroscopy (EDS) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) confirm the achieved stoichiometry. X-ray diffraction (XRD) well identifies the layered structure unit cell, and Raman spectroscopy displays the corresponding M-O bonds motions. The cycling voltammetry (CV) of LiNi0.2Co0.2Al0.1Mn0.45O2 in lithium half-cell reveals an electrochemical process characterized by a remarkable irreversible oxidation taking place at 4.6 V vs. Li+/Li during the first scan, and subsequent reversible Li (de)intercalation centered at 3.8 V vs. Li+/Li with interphase resistance limited to 16 Ω upon activation as indicated by electrochemical impedance spectroscopy (EIS). The relevant irreversibility during first charge is also detected by galvanostatic cycling in a lithium half-cell subsequently operating at an average voltage of 3.8 V with a stable trend, and a maximum specific capacity of 130 mAh g−1. The initial irreversible capacity of the layered cathode is advantageously exploited for compensating the pristine inefficiency of the Li-alloying composite anode in a proof-of-concept Li-ion battery achieved by combining the LiNi0.2Co0.2Al0.1Mn0.45O2 with a silicon oxide composite (SiOx-C) without any preliminary pre-treatment of the electrodes. The full-cell displays a cycling behavior strongly influenced by the anode/cathode ratio, and the corresponding EIS performed both on the single electrodes and on the Li-ion cell by using an additional lithium reference suggests a controlling role of the anode interphase and possible enhancements through a slight excess of cathode material.