High Energy Density Li-ion Batteries Research Articles

Operando chemo-mechanical evolution in LiNi0.8Co0.1Mn0.1O2 cathode

Abstract Ni-rich LiNixCoyMnzO2 (NCMxyz, x + y + z = 1, x ≥ 0.8) layered oxide materials are considered as the main cathode materials for high energy density Li-ion batteries. However, the endless cracks of polycrystalline NCM materials caused by stress accelerate the loss of active materials and electrolyte decomposition, limiting the cycle life. Hence, understanding the chemo-mechanical evolution during (de)lithiation of NCM materials is crucial to the performance improvement. In this work, an optical fiber with με resolution is designed to in operando detect the stress evolution of polycrystalline LiNi0.8Co0.1Mn0.1O2 (P-NCM811) cathode during cycling. By integrating the sensor inside the cathode, the stress variation of P-NCM811 is completely transferred to the optical fiber. We find that the anisotropy of primary particles leads to the appearance of structural stress, inducing the formation of microcracks in polycrystalline particles, which is the main reason for capacity decay. The isotropy of primary particles reduces the structural stress of polycrystalline particles, eliminating the generation of microcracks. Accordingly, the P-NCM811 with the ordered arrangement structure deliver high electrochemical performance with capacity retention of 82% over 500 cycles. This work provides a brand-new view for understanding the operando chemo-mechanical evolution of NCM materials during battery operation and guiding the design of electrode materials for rechargeable batteries.

Evaluating Polyacrylic Acid as a Universal Aqueous Binder for Ni-Rich Cathodes NMC811 and Si Anodes in Full Cell Lithium-ion Batteries.

Silicon (Si) and silicon/graphite (Si/Gr) composite anodes are promising candidates due to their high theoretical capacity, low operating potential and natural abundance for high energy density Li-ion batteries. Green electrode production, eliminating organic volatile solvents require advancement of aqueous electrodes. Engineering the binder plays a critical role for improving waterborne electrodes. Lithium substituted polyacrylic acid LiPAA has been demonstrated as a promising binder for Si/Gr anodes and for Ni-rich cathodes in different cell configurations. LiPAA is utilized to minimize the volume expansion during cycling for Si/Gr anodes. LiPAA is formed in situ during cathode slurry preparation to regulate the pH and dimmish the Li loss. Using advanced characterization techniques, we investigated the slurries, electrodes, and active material reaction with LiPAA and its effect to the cycling performance. Our results indicate that the performance of high Si containing anode is limited by the amount of Si in the electrode. The failure mechanism with respect to high Si content was studied thoroughly. Aqueous processed cathodes with LiPAA binder in combination with Si anodes outperformed NMP based cathodes. Hence, LiPAA was successfully utilized as an active binder for both a high Si containing anode and for a Ni rich cathode.

Synergistically enhanced LiF–rich protective layer for highly stable silicon anodes

Silicon (Si) is considered as one of the most promising anode materials with an extremely high specific capacity (3579 mAh/g), which is beyond the limit of conventional graphite anodes in lithium (Li) ion batteries (LIBs). However, large volume changes during the lithiation/delithiation process and formation of an unstable solid electrolyte interface (SEI) layer hinder the practical application of Si anodes. To address these issues, constructing a stable protective layer at the interface between anode and electrolyte is a desirable strategy. In this study, a LiF-rich SEI inducing protective layer (LPL) comprising aluminum fluoride (AlF3) and poly(acrylic acid) (PAA) is introduced onto Si anode to construct a stable LiF–rich SEI layer and mitigate the volume changes of the Si anodes during cycling. Owing to the synergetic effects of AlF3 and PAA, a LiF-rich SEI layer with robust physicochemical properties is uniformly formed on the Si anode. As a result, the LPL coated Si (LPL@Si) anodes exhibit outstanding electrochemical properties in Li metal cell tests. In addition, a full-cell prepared with the LPL@Si anode and LiNi0.8Co0.1Mn0.1O2 as a cathode exhibits an excellent cycling performance and mitigated volume changes, demonstrating the potential of this strategy to protect the Si anodes for the development of high-energy–density LIBs.

Systematic study of Co-free LiNi0.9Mn0.07Al0.03O2 Ni-rich cathode materials to realize high-energy density Li-ion batteries

The growing use of EVs and society's energy needs require safe, affordable, durable, and eco-friendly high-energy lithium-ion batteries (LIBs). To this end, we synthesized and investigated the removal of Co from Al-doped Ni-rich cathode materials, specifically LiNi0.9Co0.1Al0.0O2 (NCA-0), LiNi0.9Mn0.1Al0.0O2 (NMA-0), LiNi0.9Mn0.07Al0.03O2 (NMA-3), intending to enhance LIB performance and reduce the reliance on cobalt, a costly and scarce resource. Our study primarily focuses on how the removal of Co affects the material characteristics of Ni-rich cathode material and further introduces aluminum into the cathode composition to study its impacts on electrochemical properties and overall performance. Among the synthesized samples, we discovered that the NMA-3 sample, modified with 3 mol% of Al, exhibited superior battery performance, demonstrating the effectiveness of aluminum in promoting cathode stability. Furthermore, the Al-modified cathode showed promising cycle life under normal and high-temperature conditions. Our NMA-3 demonstrated remarkable capacity retention of ∼ 88 % at 25 °C and ∼ 81 % at 45 °C after 200 cycles at 1C, within a voltage range of 2.8–4.3 V, closely matching the performances of conventional NCM and NCA cathodes. Without cobalt, the cathodes exhibited increased cation disorder leading to inferior rate capabilities at high C-rates. In-situ transmission XRD analysis revealed that the introduction of Al has reduced the phase change and provided much-needed stability to the overall structure of the Co-free NMA-3. Altogether, the findings suggest that our aluminum-modified NMA-3 sample offers a promising approach to developing Co-free, Ni-rich cathodes, effectively paving the way toward sustainable, high-energy–density LIBs.

10 mAh cm−2 Cathode by Roll‐to‐Roll Process for Low Cost and High Energy Density Li‐Ion Batteries

AbstractRoll‐to‐roll dry processing enables the manufacture of high energy density and low cost Li‐ion batteries (LIBs). However, as the thickness of the electrode fabricated by dry processing becomes greater (≥10 mAh cm−2), Li‐ion migration resistance (Rion) and charge‐transfer resistance (Rct) in the electrode dramatically increase due to long diffusion lengths for Li‐ion and electron. Therefore, it is important to reduce diffusion lengths in the electrode to achieve high energy density LIBs. The dry electrode with a high areal capacity of 10 mAh cm−2 and low resistance can be achieved by following three characteristics. First, the fibrillization behavior of polytetrafluoroethylene (PTFE) binder is controlled by adjusting the processing temperature during the fibrillization process, which enables uniform distribution of PTFE binder and carbon black (CB). Second, pore size/distribution and conducting network are engineered by multi‐dimensional conducting agents, enhancing Li‐ions and electrons transport in the electrode. Finally, the structural integrity of LiNi0.80Co0.15Al0.05O2 (NCA) particles is improved without fractures, which enables uniform pore distribution in the electrode by controlling the calendering step. The prepared 10 mAh cm−2 dry electrode with homogeneous microstructure shows reduced Rion and Rct due to short diffusion lengths, which improves electrochemical performances in LIBs with a high volumetric energy density of ≈710 Wh L−1.

Effective Cu-Fe oxide/ multidimensional nanocarbon-coupled ternary composite-based anode: Mechanistic insight into interface tuning for swift Li-ion diffusion

This work focused on engineering the hybrid nanocomposite-based anode comprising CuFe2O4 (CFO), reduced graphene oxide (RG), and functionalized carbon nanotubes (FC) to investigate its Li-ion storage kinetics. The ternary nanocomposites CFO/RG/FC (CFO-C) demonstrated a specific capacity (SC) of 760 mAh/g at a Cdensity of 200 mA/g after 100 electrochemical charge-discharge cycles and an SC of 450 mAh/g at a high Cdensity of 500 mA/g after 300 electrochemical cycles. Results revealed that the addition of RG and FC aided in enhancing the electrical transport at the interface, in turn, it assisted in augmenting the Li-ion storage capability from ∼240 to ∼760 mAh/g at the end of 100 charge-discharge cycles with a Cdensity of 200 mA/g. RG and FC acted as anchoring sites for CFO and spacer, respectively, which resulted in improved electrical transport to accelerate Li-ion diffusion transport by fivefold. Such composite anode is a probable candidate as the high-performance anode in designing high-energy density Li-ion battery applications.

Low-cost micron-sized silicon/carbon anode prepared by a facile ball-milling method for Li-ion batteries

Commercially, Si nanoparticles (nano Si) are blended with graphite to construct high-capacity Si/C anodes. However, this strategy falls short because of the high cost of nano Si, serious pollution due to the use of organic solvent, and weak physical-electrical connection between graphite and Si. Herein, using low-cost micron-sized Si (μSi) and graphite as the raw materials, we proposed a facial ball-milling method to construct high-performance Si/C anode (μSi/C@CH) in which milled Si particles are protected both by graphite matrix and homogeneous chitosan-derived carbon layer. It is shown that the N and O atoms not only tend to coordinate with Li+, generating uniformly-distributed Li+ transport channels, but also improve the electrical conductivity of the anode materials. As a result, μSi/C@CH shows high cycling stability (376.7 mAh g-1 at 0.5 A g-1 after 500 cycles) and good rate capability of 120.2 mAh g-1 at 5 A g-1. This dual protection strategy facilitates the practical application of Si/C materials in high-energy density Li ion batteries (LIBs).

Electrochemical Scanning Probe Microscopy Evaluation of Li-Ion Battery Cathode Degradation through in Situ Oxygen Evolution Measurement and Interfacial Property Characterization

Degradation processes involving oxygen evolution significantly limit the performance, reversibility, and capacity of high energy density Li-ion battery (LiB) cathodes. In addition, oxygen evolution processes create hazardous conditions for LiB operation. Despite the importance of these processes, characterization of evolved O2 with sufficient spatial and temporal versatility is hampered by the complex setups required to perform electrochemical mass spectrometry, the gold standard for evaluating this process. Recently, we introduced a scanning electrochemical microscopy (SECM) approach that enables in-situ, real-time (i.e., few ms temporal resolution), chemically selective detection of O2.[1] Measurements were accomplished by positioning an SECM probe (i.e., an Au ultramicroelectrode) near operating cathode surfaces for detecting O2 via the oxygen reduction reaction (ORR). The superior signal-to-noise of this method enabled the observation of two peaks corresponding to a steady-state evolution at high voltage and a transient O2 evolution at low voltage on materials such as lithium cobalt oxide (LCO) and NMC electrodes.Here, we expand the capabilities of our technique by incorporating correlated measurements aimed at understanding how oxygen evolution profiles are related to surface electrochemical and mechanical properties. Specifically, we will focus on the use of feedback-mode SECM and the use of reactive mediators to evaluate the changes in the rates of electron transfer measured on materials undergoing O2 and after structural degradation. Furthermore, the use of electrochemical AFM allows us to measure the mechanical properties of these interfaces, in an attempt to tie the structural changes and the evolution of oxidizing species with the formation of cathode-electrolyte interfaces. Altogether, these multimodal SECM and AFM methods elucidate the manifold chemical, structural, and performance changes underpinning LiB cathode operation.[1] Mishra, A.; Sarbapalli, D.; Hossain, M.S.; Gossage, Z.T.; Li, Z.; Urban, A.; Rodríguez-López, J. Highly Sensitive Detection and Mapping of Incipient and Steady-State Oxygen Evolution from Operating Li-Ion Battery Cathodes via Scanning Electrochemical Microscopy. J. Electrochem. Soc., 2022, 169, 086501. Figure 1

Temperature-Dependent Interplay of Chemical Versus Electrochemical Electrolyte Oxidation at Ni-Rich Cathodes

Increasing demands for high energy density Li-ion batteries as a source for power supply are demanding an optimization of cathode active materials (CAMs) and of the overall cell chemistry of batteries. Thus, the main interest of researchers has focused on nickel-rich (>80%) layered transition metal oxides such as NCMs (LiNixCoyMnzO2, with x+y+z=1) or NCAs (LiNixCoyAlzO2, with x+y+z=1) as CAMs, owing to their high capacity. However, as a result of the increase in Ni-content, the structural stability of these CAMs is significantly decreased at high upper cut-off potentials compared to those with lower Ni-content, resulting in capacity fading, which restricts their practically achievable capacity.[1] One possible culprit behind this capacity fading at high state-of-charge (SOC) is the release of reactive lattice oxygen, which is known for layered TM-oxides to occur at high SOC (i.e., starting at approx. 80% SOC).[2] The released oxygen is proposed to lead to the chemical oxidation of ethylene carbonate (EC), resulting in HF formation, which in turn is proposed to trigger the dissolution of TMs.[3] Furthermore, the electrochemical oxidation of the electrolyte is known to occur at high potentials, which as a result of its reactive reaction products, can induce further transition metal (TM) dissolution from the CAM.[4,5] The proposed chemical oxidation of the electrolyte by lattice oxygen suggests that this process should be strongly correlated to the dissolution of TMs from the CAM. However, as shown by operando X-ray absorption spectroscopy (XAS) and on-line electrochemical mass spectroscopy (OEMS) studies, the onset for the TM-dissolution, depending on the CAM under investigation, occurs at ~300 mV higher potentials compared to the onset for oxygen evolution.[2,3] This suggests that the dissolution of metals is rather induced by the electrochemical oxidation of the carbonate-based electrolyte, which was reported to initiate at potentials above 4.7 VLi at room temperature.[5] Both the electrochemical oxidation of battery electrolytes, as well as the dissolution of TMs from the CAM were reported to be strongly affected by temperature, while the onset potential for lattice oxygen loss is essentially unaffected, which further hints towards the significance of former.[5-7] Within this work we therefore conduct a detailed study on the temperature dependency of both the gas formation due to (electro)chemical electrolyte oxidation and the dissolution of TMs by means of OEMS and operando hard XAS, respectively. By applying a measurement protocol consisting of constant voltage-holds in steps of 50 mV at elevated potentials (see Figure 1), an excellent time as well as potential resolution enables the deconvolution of the onset for lattice oxygen release and the (electro)chemical oxidation of LP47 (1 M LiPF6 in EC:DEC 3:7 by weight) for a LiNi0.80Co0.15Al0.05O2 (NCA) CAM via OEMS. It will be shown that the onset for oxygen evolution coincides with a significant evolution of CO2 (see Figure 1b), indicating chemical oxidation of the electrolyte. However, the onset for POF3/PF5 evolution (marked in Figure 1b as “POF3”, since both gasses appear on the same mass channel)[8], which is a reaction product from the decomposition of LiPF6 caused by electrochemical electrolyte oxidation, is shifted to 300 – 450 mV higher potentials (depending on the temperature). It suggests a chemical oxidation mechanism of the electrolyte, which proceeds without significant H2O/H+ production. A change in temperature strongly affects this onset of “POF3” evolution, while O2 is released at the same degree of de-lithiation, regardless of temperature. To correlate this effect observed in the temperature-dependent gassing behavior to the dissolution of transition metals for this CAM, an operando hard XAS study at different temperatures will be conducted.

(Invited) Challanges with Novel Binders for LiNi0.5Mn1.5O4 li-Ion Battery Electrodes

In the search for high-energy density Li-ion battery electrode materials which are also comparatively sustainanble, LiNi0.5Mn1.5O4 (LNMO) is often targeted as a promising next-generation alternative. While the capacity of LNMO is limited, it has a high operating voltage around 4.7 V vs. Li+/Li, and the spinel structure of the materials renders useful power capacilities. Moreover, it is a cobalt-free cathode. However, fabricating functional electrodes have shown problematic due to inherent instabilities at both bulk and surfaces, where especially operation at elevated temperatures has shown to cause capacity degradation. Problems comprise structural changes, loss of oxygen, and Mn dissolution, often interconnected with each other. One strategy to improve stabilization would be through coatings of the LNMO particles, either inorganic or organic.The polymer binder used for battery processing is inherently an organic coating layer, since it wraps around the particles of the electrodes. Thereby, binders has been shown to being able to add functionalities to electrode materials, e.g. to improve electronic conductivity, add storage capacity or mitigate side-reactions. The binder is at interplay with the reactions causing interphase layer formation. Thereby, changing or taioring the binder can cause direct improvements in cell performance.Poly(vinylidene difluoride) (PVdF) and its many derviates is since long time the standard for Li-ion battery electrodes, despite not being particular sustainable and being dependent on toxic solvents such as N-methyl-2-pyrrolidone (NMP). LNMO is, in this context, no exception. Nevertheless, while PVdF is chemically intert, it provides little other capabilities to the battery electrodes, and other binder systems could improve in this context: either through electochemica performance or through being more sustainable.Here, two other binder systems for LNMO are discussed: polyacrylonitrile (PAN) and polyacrylic acid (PAA). Polynitriles are often promoted as being comparatively stable at higher potentials, while also being ionically conductive, and should therefore in principle add functionalities into the resulting electrodes. PAA, on the other hand, has shown good adhesion and adherence to oxide surfaces, and can thereby form more robust interfacial layers on the cathode. We show here, however, that challenges remain for these alternative binder systems, not least due to the high operating potential of LNMO electrodes which cause side-reactions of both types of alternative binders. These side-reactions are their products are analyzed through a range of methods, e.g. photoelectron spectroscopy, electron microscopy and electroanalytical techniques, thereby providing guidance to the development of novel binders for high-voltage electrodes.

Constructing a stable interface on Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode via lactic acid-assisted engineering strategy

Ni-rich layered oxides are potential cathode materials for next-generation high energy density Li-ion batteries due to their high capacity and low cost. However, the inherently unstable surface properties, including high levels of residual Li compounds, dissolution of transition metal cations, and parasitic side reactions, have not been effectively addressed, leading to significant degradation in their electrochemical performance. In this study, we propose a simple and effective lactic acid-assisted interface engineering strategy to regulate the surface chemistry and properties of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode. This novel surface treatment method successfully eliminates surface residual Li compounds, inhibits structural collapse, and mitigates cathode-electrolyte interface film growth. As a result, the lactic acid-treated LiNi0.8Co0.1Mn0.1O2 achieved a remarkable capacity retention of 91.7% after 100 cycles at 0.5 C (25 °C) and outstanding rate capability of 149.5 mA h g−1 at 10 C, significantly outperforming the pristine material. Furthermore, a pouch-type full cell incorporating the modified LiNi0.8Co0.1Mn0.1O2 cathode demonstrates impressive long-term cycle life, retaining 81.5% of its capacity after 500 cycles at 1 C. More importantly, the thermal stability of the modified cathode is also dramatically improved. This study offers a valuable surface modification strategy for enhancing the overall performance of Ni-rich cathode materials.

Dual regulation mechanism of MoS2/MoO3 heterostructure for polysulfide and volume effect enables stable and durable lithium storage

Current commercial Li-ion batteries (LIBs) with graphite anode are unable to meet the actual demand due to their low energy density. Recently, MoO3 possesses 1117 mAh/g high theoretical specific capacity has received a wide attention and is regarded as a promising anode material. However, the low intrinsic electronic conductivity and the large volume effect of MoO3 limited the practical application. Given the typical MoS2 anode materials with high electron conductivity and discharge capacity, in this work, we designed a 2D hierarchical MoS2/MoO3 nanocomposite. As expected, the large exposed edges and layered MoS2 provide sufficient channels for rapid ion diffusion while improving the volume variation and conductivity of MoO3. Nevertheless, as an anode material, MoS2 suffers from severe and undesired sulfur loses during cycling, resulting in rapid capacity degradation. It is found that MoO3 and intercalation state (LixMoO3) characters a strong chemical adsorption property that have been demonstrated to be effectively promoting the conversion of soluble lithium polysulfides, thereby enhancing the kinetics of sulfur conversion. Inspired with such multifunction structural design strategy, the MoS2/MoO3 anode achieves a remarkable specific capacity (1255.7 mAh/g) and long cycling life (1300 cycles). Subsequently, coupled with LiFePO4 cathode, the full cells achieved a 129 mAh/g competitive capacity and the retention rate is as high as 99.3% after 100 cycles. This work provides an inspired strategy and routes to realize a high energy density LIBs.

(Invited) High-Throughput Development of LiCoPO4

High voltage cathodes are attractive for high energy density Li-ion batteries, particularly with the innovation of solid electrolytes with large stability windows. However, candidates such as LiCoPO4 have presented numerous problems due to poor electronic/ionic conductivities. Typical solutions involving nanosizing result in extremely poor cycling performance. Herein, we first apply high-throughput methods to develop near-micron sized carbon-coated LiCoPO4 with improved energy density and capacity retention.1 In total, 1300 materials with 46 different substituents were synthesized and characterized. A number of substituents showed greatly improved capacity (e.g. 160 mAh/g for 1% In substitution vs. 95 mAh/g for the pristine). However, co-doping was required to improve extended cycling. Li1-3xCo1-2xInxMoxPO4 was found to be particularly effective with dramatically improved cycling (as high as 100 % after 10 cycles, vs. ~50 % in unsubstituted). While In improved the electronic conductivity of the carbon-coated materials, Mo co-doping gave larger particles and DFT calculations showed that Mo impedes the formation of Li/Co antisite defects.While the above described experiments were solely guided by the researchers intuition, we also explore potential benefits of using machine-learning (ML) algorithms to guide the composition exploration. Random compositions were first prepared to supplement our existing data as part of the training set, then further synthesis was performed based on the ML outputs. The results will be presented in detail to help establish to what extent ML can be used to further leverage our group's high-throughput data.

Doping of group IVB elements for nickel-rich cobalt-free cathodes

Hetero-element doping is a promising strategy to improve the cycling stability of nickel-rich cobalt-free cathodes for the next-generation high energy-density Li ion batteries. To make doping effective, it is important to understand the mechanism of how the dopants regulate the electronic band, lattice parameter adjusting, or hetero-phase formation to achieve high stability. In this study, we investigate LiNi0.9Mn0.1O2 cathodes doped with IVB grouping elements via multiple characterization techniques. By utilizing in situ XRD and TEM methods, we found that the stronger Ti–O bond effectively improves the cathode stability via a dual protection mechanism. Specifically, the bulk lattice of cathode is well-preserved during cycling as a result of the suppressed H2-H3 phase transition, while a in situ formed Ti-rich surface layer can prevent continuous surface degradation. As a result, the 5% Ti doped LiNi0.9Mn0.1O2 cathode exhibits a high capacity retention of 96% after 100 cycles. Whereas, despite IVB group elements Zr and Hf have stronger bonding energy with oxygen, their larger ionic radii actually impede their diffusion into the cathode, thereby they can not improve the cycling stability. Our findings uncover the functional origin of doped elements with their dynamic modification on cathode structure, providing mechanistic insights into the design of nickel-rich cobalt-free cathodes.

A Multifunctional Interlocked Binder with Synergistic In Situ Covalent and Hydrogen Bonding for High-Performance Si Anode in Li-ion Batteries.

Silicon has garnered significant attention as a promising anode material for high-energy density Li-ion batteries. However, Si can be easily pulverized during cycling, which results in the loss of electrical contact and ultimately shortens battery lifetime. Therefore, the Si anode binder is developed to dissipate the enormous mechanical stress of the Si anode with enhanced mechanical properties. However, the interfacial stability between the Si anode binder and Cu current collector should also be improved. Here, a multifunctional thiourea polymer network (TUPN) is proposed as the Si anode binder. The TUPN binder provides the structural integrity of the Si anode with excellent tensile strength and resilience due to the epoxy-amine and silanol-epoxy covalent cross-linking, while exhibiting high extensibility from the random coil chains with the hydrogen bonds of thiourea, oligoether, and isocyanurate moieties. Furthermore, the robust TUPN binder enhances the interfacial stability between the Si anode and current collector by forming a physical interaction. Finally, the facilitated Li-ion transport and improved electrolyte wettability are realized due to the polar oligoether, thiourea, and isocyanurate moieties, respectively. The concept of this work is to highlight providing directions for the design of polymer binders for next-generation batteries.

Antioxidant layer enables chemically stable cathode-electrolyte interface towards durable and safe Li-ion batteries

Although nickel-rich layered lithium transition metal oxides are one of the most promising candidates for high energy-density Li-ion batteries in electric vehicle applications, they yet suffer from irreversible capacity fading and poor safety properties due to the unstable cathode-electrolyte interphase (CEI), especially at high voltage and high temperature. This instability is mainly caused by the attack of free radicals generated from electrolyte decomposition and active oxygen species (especially singlet oxygen) released from the surface lattice. Here, we propose a novel modification method to construct a protective antioxidant layer on the surface of LiNi0.8Co0.1Mn0.1O2 (NCM). By scavenging free radicals and singlet oxygen, the antioxidant layer greatly reduces the interfacial side reactions and significantly suppresses irreversible rock-salt phase transitions and the associated oxygen species release, leading to the stabilization of the interface. As a result, superior electrochemical performance and enhanced thermal stabilities are achieved. Specifically, the modified NCM exhibits a capacity retention of 92.0% over 1000 cycles in full cells and a dramatic increase of onset temperature (T1) from 75.2 °C to 114.2 °C. This antioxidant layer modification by scavenging free radicals and singlet oxygen provides a new strategy for addressing challenges of CEI design, which is theoretically applicable to all layered transition metal oxide cathode materials.

Low-Temperature-Aged Synthesis of CeO2-Coated Li-Rich Oxide as Cathode for Low-Cost High-Energy Density Li-Ion Batteries

Co-free Li-rich oxide shows promise as a cathode for low-cost high-energy density Li-ion batteries but presents poor cyclic stability. To address this issue, a novel CeO2-coated Li-rich oxide composite is developed by applying a layer of CeO2 onto Co-free Li-rich oxide through a low-temperature-aged process. With this uniform coating, the resulting composite presents improved cyclic stability as well as rate capability as the cathode of a Li-ion battery. The capacity retention of the resulting composite is increased from 67% to 85% after 100 cycles, and its capacity retention of 5 C/0.05 C is enhanced from 10% to 23% compared with the uncoated sample. Such significant improvements indicate that this low-temperature-aged process is promising for preparing Co-free Li-rich oxides as cathodes of low-cost high-energy density Li-ion batteries.

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.

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.

Artificial interface modification of Ni-rich ternary cathode material to enhance electrochemical performance for Li-ion storage through RF-plasma-assisted technique

Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) is a promising high-performance cathode material for large-scale Li-ion storage applications. However, devices consisting of Ni-rich materials are less thermally stable, and several factors hinder their use in practical high-energy–density applications. Herein, an approach for plasma-modified NCM811 with TiN is proposed to effectively improve the electrochemical performance and stabilize the cathode–electrolyte interface reaction. In addition, the following aspects are systematically investigated using different techniques: (i) physicochemical properties; (ii) Li storage performance, particularly, cyclic/rate capacity, kinetic behavior of the lithium-ion diffusivities, and electrical conductivity; and (iii) key factor for improving the electrochemical performance through ex-situ/in-situ investigations. The NCM811-TiN/graphite pouch cell displays a high reversible capacity of 17.5 mAh and sustains over 200 cycles at 1C. Comprehensive characterization and probes indicate that the TiN interface with the NCM electrode enhances thermal stability, cyclic capacity, and rate stability without changing the bulk structure and morphology. Hence, these findings facilitate the practical use of safe and high-energy–density Li-ion batteries.