Constructing a Protective Pillaring Layer by Incorporating Gradient Mn4+ to Stabilize the Surface/Interfacial Structure of LiNi0.815Co0.15Al0.035O2 Cathode

Tuning the Interface Stability of Nickel-Rich NCM Cathode Against Aggressive Structural Collapse via the Synergistic Effect of Additives

Nickel-rich layered oxides are envisaged as one of the most promising alternative cathode materials for lithium-ion batteries, considering their capabilities to achieve ultrahigh energy density at an affordable cost. Nonetheless, with increasing Ni content in the cathodes comes a severe extent of Ni4+ redox side reactions on the interface, leading to fast capacity decay and structural stability fading over extended cycles. Herein, dual additives of bis(vinylsulfonyl)methane (BVM) and lithium difluorophosphate (LiDFP) are adopted to synergistically generate the F-, P-, and S-rich passivation layer on the cathode, and the Ni4+ activity and dissolution at high voltage are restricted. The sulfur-rich layer formed by the polymerization of BVM, combined with the Li3PO4 and LiF phases derived from LiDFP, alleviates the problems of increased impedance, cracks, and an irreversible H2-H3 phase transition. Consequently, the Ni-rich LiNixM1-xO2 (x > 0.95) button half-cell cycled in LiDFP + BVM electrolyte exhibits a significant discharging capacity of 181.4 mAh g-1 at 1  C (1  C = 200 mA g-1) with retention of 83.7% after 100 cycles, surpassing the performance of the commercial electrolyte (160.7 mAh g-1) with retention of 53.3%. Remarkably, the NCM95||graphite pouch cell exhibits a remarkable capacity retention of 95.5% after 200 cycles. This work inspires the rational design of electrolyte additives for ultrahigh-energy batteries with nickel-rich layered oxide cathodes.

Kirkendall effect-induced uniform stress distribution stabilizes nickel-rich layered oxide cathodes

Nickel-rich layered oxide cathodes promise ultrahigh energy density but is plagued by the mechanical failure of the secondary particle upon (de)lithiation. Existing approaches for alleviating the structural degradation could retard pulverization, yet fail to tune the stress distribution and root out the formation of cracks. Herein, we report a unique strategy to uniformize the stress distribution in secondary particle via Kirkendall effect to stabilize the core region during electrochemical cycling. Exotic metal/metalloid oxides (such as Al2O3 or SiO2) is introduced as the heterogeneous nucleation seeds for the preferential growth of the precursor. The calcination treatment afterwards generates a dopant-rich interior structure with central Kirkendall void, due to the different diffusivity between the exotic element and nickel atom. The resulting cathode material exhibits superior structural and electrochemical reversibility, thus contributing to a high specific energy density (based on cathode) of 660 Wh kg-1 after 500 cycles with a retention rate of 86%. This study suggests that uniformizing stress distribution represents a promising pathway to tackle the structural instability facing nickel-rich layered oxide cathodes.

A new high-valence cation pillar within the Li layer of compositionally optimized Ni-rich LiNi0.9Co0.1O2 with improved structural stability for Li-ion battery

Elevating the nickel (Ni) content within layered cathodes constitutes a straightforward and effective approach to enhance the energy density of lithium-ion batteries (LIBs). However, the phase transition from H2 to H3 introduces substantial alterations in lattice volume, leading to structural degradation and diminished electrochemical performance. This study employs density functional theory (DFT) calculations to determine that the formation energy for Nb5+ occupied at Li 3b sites is lower compared to that of Ni 3a and Co 3a sites, yet higher than that of Mn 3a sites. This suggests a preference for Nb5+ doping within the Li layer of Mn-free cathodes. Motivated by these DFT results, we show the viability of high-valence Nb5+ as a stable pillar in the compositionally optimized binary oxide LiNi0.9Co0.1O2. The inclusion of this Nb5+ pillar in the Li layer of Ni/Co-based oxide significantly enhances the reversibility of the H2-H3 redox couple and mitigates microcrack formation in polycrystalline cathodes. As a result, the Nb-doped Ni/Co-based cathode exhibits an extended cycling lifespan, elevated rate capability, and increased thermal stability compared to the undoped. This investigation achieves precise control over doping sites by optimizing the chemical composition of Ni-rich cathodes and provides novel insights into advancing their electrochemical performance for high-energy LIBs.

Preparation of long-term cycling stable ni-rich concentration-gradient NCMA cathode materials for li-ion batteries

Nickel-rich (Ni > 90 %) cathodes are regarded as one of the most attractive because of their high energy density, despite their poor stability and cycle life. To improve their performance, in this study we synthesized a double concentration-gradient layered Li[Ni_0.90Co_0.04Mn_0.03Al_0.03]O₂ oxide (CG-NCMA) using a continuous co-precipitation Taylor-Couette cylindrical reactor (TCCR) with a Ni-rich-core, an Mn-rich surface, and Al on top. The concentration-gradient morphology was confirmed through cross-sectional EDX line scanning. The as-synthesized sample exhibited excellent electrochemical performance at high rates (5C/10C), as well as cyclability (91.5 % after 100 cycles and 70.3 % after 500 cycles at 1C), superior to that (83.4 % and 47.6 %) of its non-concentration-gradient counterpart (UC-NCMA). The Mn-rich surface and presence of Al helped the material stay structurally robust, even after 500 cycles, while also suppressing side reactions between the electrode and electrolyte, resulting in better overall electrochemical performance. These enhancements in performance were studied using TEM, SEM, in-situ-XRD, XPS, CV, EIS and post-mortem analyses. This synthetic method enables the highly scalable production of CG-NCMA samples with two concentration-gradient structures for practical applications in Li-ion batteries.

Insight into the Surface Reconstruction-Induced Structure and Electrochemical Performance Evolution for Ni-Rich Cathodes with Postannealing after Washing

Ni-rich layered LiNixCoyAlzO2 (NCA, x ≥ 0.8) oxides have attracted wide attention as cathode materials for lithium-ion batteries due to their higher energy density and lower cost. However, the increase in the capacity for Ni-rich cathodes can cause faster capacity decay and increase sensitivity to ambient air exposure during the storage process. Especially, the residual lithium on the surface of Ni-rich cathodes will cause severe flatulence during cycling which greatly reduces the safety performance of the battery. Washing is an effective method to reduce residual lithium, but it will seriously damage the surface phase structure of Ni-rich materials. Here, we introduce a designed method involving two steps, washing and high-temperature annealing, which can ingeniously modify the surface phase structure of Ni-rich cathodes. The results show that the residual lithium content can be significantly reduced. The thin NiO-like rock-salt phase formed on the surface of Ni-rich cathode annealed at 600 °C improves the diffusion kinetics of Li+, reduces the polarization, and improves the electrochemical performance of Ni-rich materials, while the thick spinel-like phase formed at 400 °C hinders the diffusion kinetics of Li+, significantly increases the polarization, and eventually leads to the structural degradation of Ni-rich materials. As a result, the discharge capacity of the cathode annealed at 600 °C still retains 174.48 mA h g-1 after 100 cycles, with a capacity retention of 92.04%, much larger than the cathode annealed at 400 °C, for which the discharge capacity drops to 107.77 mA h g-1, with a capacity retention of 65.78%.

Utilizing dual functions of LaPO4to enhance the electrochemical performance of LiNi0.87Co0.09Al0.04O2cathode material

In this paper, via a facile wet coating method, the LaPO₄coating layer has been introduced onto the LiNi_0.87Co_0.09Al_0.04O₂(NCA) surface while a small part of La³⁺has also been doped on the surface to realize the dual functions modification of coating and doping. The morphology and structure of the samples were investigated by XRD, SEM and TEM measurements. The chemical compositions of the samples were analyzed via EDS and XPS data. The results showed that the coating of LaPO₄and the doping of La³⁺were successfully achieved on the surface of NCA. Electrochemical tests indicate that the sample modified with 2 wt% LaPO₄(L2-NCA) possesses the best electrochemical performance. After 100 cycles, compared with the capacity retention rate of pristine NCA of 87.1%/74.2% at 0.5 C at 25 °C/60 °C, L2-NCA showed better cycling stability, and the capacity retention rate increased to 96.0%/85.1%, respectively. Besides, the rate performance of the modified samples at 1 C, 2 C and 5 C were also significantly improved. These satisfactory results reveal that the surface modification of LaPO₄provides a feasible scheme to uprate the performance of Ni-rich cathode materials.

The influence of water in electrodes on the solid electrolyte interphase film of micro lithium-ion batteries for the wireless headphone

During the production of micro lithium-ion batteries (LIBs), which are widely used in wireless headphones and other small portable devices, numerous factors can affect their quality, among which the content of water plays a crucial role. In this work, the influence of water in electrodes on the performances of micro LIBs is studied deeply. When the content of water increases, both the rate performance and the cycling performance of the batteries fade. The discharge capacity retention of the battery from high water content sample group H (group H) is 81.81% after 350 cycles at 2C, while that of the battery from low water content sample group L (group L) is 89.89% under the same condition. As for the rate performance, the discharge capacity of group H is only 58.66% of group L at 5C. To take a step further, it is mainly because an overgrowth of the solid electrolyte interphase film happen with the growth of water content. Accordingly, excess lithium ions are consumed and the porous structure of the anode is destroyed. Considering the results above, we believe that this work can offer a theory foundation to carry out the failure analysis of micro batteries.

Dual-Modified Compact Layer and Superficial Ti Doping for Reinforced Structural Integrity and Thermal Stability of Ni-Rich Cathodes

Nickel-rich layered oxides have been regarded as a potential cathode material for high-energy-density lithium-ion batteries because of the high specific capacity and low cost. However, the rapid capacity fading due to interfacial side reactions and bulk structural degradation seriously encumbers its commercialization. Herein, a highly stable hybrid surface architecture, which integrates an outer coating layer of TiO₂&Li₂TiO₃ and a surficial titanium doping by incorporated Ti₂O₃, is carefully designed to enhance the structural stability and eliminate lithium impurity. Meanwhile, the surficial titanium doping induces a nanoscale cation-mixing layer, which suppresses transition-metal-ion migration and ameliorates the reversibility of the H2 → H3 phase transition. Also, the Li₂TiO₃ coating layer with three-dimensional channels promotes ion transportation. Moreover, the electrochemically stable TiO₂ coating layer restrains side reactions and reinforces interfacial stability. With the collaboration of titanium doping and TiO₂&Li₂TiO₃ hybrid coating, the sample with 1 mol % modified achieves a capacity retention of 93.02% after 100 cycles with a voltage decay of only 0.03 V and up to 84.62% at a high voltage of 3.0-4.5 V. Furthermore, the ordered occupation of Ni ions in the Li layer boosts the thermal stability by procrastinating the layered-to-rock salt phase transition. This work provides a straightforward and economical modification strategy for boosting the structural and thermal stability of nickel-rich cathode materials.

Optimizing surface residual alkali and enhancing electrochemical performance of LiNi0.8Co0.15Al0.05O2cathode by LiH2PO4

LiNi_0.8Co_0.15Al_0.05O₂(NCA), a promising ternary cathode material of lithium-ion batteries, has widely attracted attention due to its high energy density and excellent cycling performance. However, the presence of residual alkali (LiOH and Li₂CO₃) on the surface will accelerate its reaction with HF from LiPF₆, resulting in structural degradation and reduced safety. In this work, we develop a new coating material, LiH₂PO₄, which can effectively optimize the residual alkali on the surface of NCA to remove H₂O and CO₂and form a coating layer with excellent ion conductivity. Under this strategy, the coated sample NCA@0.02Li₃PO₄(P2-NCA) provides a capacity of 147.8 mAh g^-1at a high rate of 5 C, which is higher than the original sample (126.5 mAh g^-1). Impressively, the cycling stabilities of P2-NCA under 0.5 C significantly improved from 85.2% and 81.9% of pristine-NCA cathode to 96.1% and 90.5% at 25 °C and 55 °C, respectively. These satisfied findings indicate that this surface modification method provides a feasible strategy toward improving the performance and applicability of nickel-rich cathode materials.

Encapsulating silicon particles by graphitic carbon enables High-performance Lithium-ion batteries

Silicon combines the advantages of high theoretical specific capacity, low potential and natural abundance, which exhibits great promise as an anode for lithium-ion batteries. However, the main challenges associated with Si anode are continuous volume expansion upon cycling and intrinsic low electronic conductivity, leading to sluggish reaction kinetics and rapid capacity fading. Herein we propose a novel in-situ self-catalytic strategy for the growth of highly graphitic carbon to encapsulate Si nanoparticles by chemical vapor deposition, where the magnesiothermic reduction byproducts are used as templates and catalysts for the formation of three-dimensional (3D) conductive network architecture. Benefiting from the improved electronic conductivity and significant suppression of volume expansion, the as-synthesized Si carbon composites exhibit excellent lithium storage capabilities in terms of high specific capacity (2126 mAh g^-1 at 0.1 A g^-1), remarkable rate capability (750 mAh g^-1 at 5 A g^-1), and good cycling stability over 450 cycles. Furthermore, the as-fabricated full cell (Si//Ni-rich LiNi_0.815Co_0.185-xAl_xO₂) shows high energy density of 395.1 Wh kg^-1 and long-term stable cyclability. Significantly, this work demonstrates the effectiveness of in-situ self-catalysis reaction by using magnesiothermic reduction byproducts catalytically derived carbon matrix to encapsulate alloy-type anode material in giving rise to the overall energy storage performance.

Cross-Talk-Suppressing Electrolyte Additive Enabling High Voltage Performance of Ni-Rich Layered Oxides in Li-Ion Batteries

Control of electrode-electrolyte interfacial reactivity at high-voltage is a key to successfully obtain high-energy-density lithium-ion batteries. In this study, 2-aminoethyldiphenyl borate (AEDB) is investigated as a multifunctional electrolyte additive in stabilizing surface and bulk of both Ni-rich LiNi_0.85 Co_0.1 Mn_0.05 O₂ (NCM851005) and graphite electrodes in a cell operated with elevated upper cutoff voltage of 4.4 V vs. Li⁺ /Li. The presence of AEDB in a full-cell inhibits structural degradation of both cathode and anode materials, suppressing crack formation, and reduces metal dissolution at the cathode and metal deposition at the anode. As a consequence, the interfacial resistance is significantly reduced. Moreover, this is a case where "the whole is greater than the sum of the parts": the effect of AEDB in half-cells is rather modest, whereas in full-cells its addition results in tremendous performance improvement. The graphite‖NCM851005 full-cell in the presence of AEDB has a capacity retention of 88 % after 100 cycles, even when the upper cutoff voltage is set to 4.35 V, corresponding to 4.4 V vs Li⁺ /Li, whereas with standard electrolyte under the same conditions it is only 21 %. The study shows a simple and easy approach to using Ni-rich cathodes in an extended voltage window and demonstrates the importance of full-cell testing for electrolyte additive selection.

Synergistic effect of uniform lattice cation/anion doping to improve structural and electrochemical performance stability for Li-rich cathode materials

There has been extensive research into lithium-rich layered oxide materials as candidates for the nextgeneration of cathode materials in lithium-ion batteries, due to their high energy density and low cost; however, their poor cycle life and fast voltage fade hinder their large-scale commercial application. Here, we propose a novel cation/anion (Na⁺/PO₄ ^3-) co-doping approach to mitigate the discharge capacity and voltage fade of a Co-free Li_1.2Ni_0.2Mn_0.6O₂ cathode. Our results show that the synergistic effect of cation/anion doping can promote long cycle stability and rate performance by inhibiting the phase transformation of the layered structure to a spinel or rock-salt structure and stabilizing the well-ordered crystal structure during long cycles. The co-doped sample exhibits an outstanding cycle stability (capacity retention of 86.7% after 150 cycles at 1 C) and excellent rate performance (153 mAh g^-1 at 5 C). The large ionic radius of Na⁺ can expand the Li slab to accelerate Li diffusion and the large tetrahedral PO₄ ^3- polyanions with high electronegativity stabilize the local structure to improve the electrochemical performance.

Fire-Preventing LiPF6 and Ethylene Carbonate-Based Organic Liquid Electrolyte System for Safer and Outperforming Lithium-Ion Batteries

Battery safety is an ever-increasing significance to guarantee consumer's safety. Reducing or preventing the risk of battery fire and explosion is a must for battery manufacturers. Major reason for the occurrence of fire in commercial lithium-ion batteries is the flammability of conventional organic liquid electrolyte, which is typically composed of 1 M LiPF₆ salt and ethylene carbonate (EC)-based organic solvents. Herein, we report the designed 1 M LiPF₆ and EC-based nonflammable electrolyte including methyl(2,2,2-trifluoroethyl)carbonate, which breaks the conventional perception that EC-based liquid electrolyte is always flammable. The designed electrolyte also provides high anodic stability beyond the conventional charge cut-off voltage of 4.2 V. A graphite∥LiNi_0.6Co_0.2Mn_0.2O₂ lithium-ion full cell with our designed EC-based nonflammable electrolyte with a small fraction of vinylene carbonate additive under an aggressive condition of 4.5 V charge cut-off voltage, 0.5C rate, and 45 °C exhibits increased capacity, reduced interfacial resistance, and improved performance and rate capability. A basic understanding of how a high-voltage cathode-electrolyte interface and anode-electrolyte interface are stabilized and how failure modes are mitigated by fire-preventing electrolyte is discussed.

Synthesis and Mechanism of High Structural Stability of Nickel-Rich Cathode Materials by Adjusting Li-Excess

It has been a long-term challenge to improve the phase stability of Ni-rich LiNi_xMn_yCo_1-x-yO₂ (x ≥ 0.6) transition metal (TM) oxides for large-scale applications. Herein, a new structure engineering strategy is utilized to optimize the structural arrangement of Li_1+x(Ni_0.88Mn_0.06Co_0.06)_1-xO₂ (NMC88) with a different Li-excess content. It was found that structure stability and particle sizes can be tuned with suitable Li-excess contents. NMC88 with an actual Li-excess of 2.7% (x = 0.027, Li/TM = 1.055) exhibits a high discharge capacity (209.1 mAh g^-1 at 3.0-4.3 V, 0.1 C) and maintains 91.7% after the 100th cycle at 1 C compared with the NMC88 sample free of Li-excess. It also performs a delayed voltage decay and a good rate capacity, delivering 145.8 mAh g^-1 at a high rate of 10 C. Multiscale characterization technologies including ex/in situ X-ray diffraction (XRD), focused ion beam (FIB) cutting-scanning electronic microscopy (SEM), and transmission electron microscopy (TEM) results show that a proper Li-excess (2.7%) content contributes to the formation of a broader Li slab, optimized cation mixing ratio, and even particle sizes. Therefore, NMC88 with a proper Li-excess is a good choice for next-generation cathode materials.

Interfacial Regulation of Ni-Rich Cathode Materials with an Ion-Conductive and Pillaring Layer by Infusing Gradient Boron for Improved Cycle Stability

Ni-rich cathodes LiNi_xCo_yAl_1-x-yO₂ (0.8 < x < 1) with high energy density, environmental benignity, and low cost are regarded as the most promising candidate materials for next-generation lithium batteries. Unfortunately, capacity fading derived from unstable surface properties and intrinsic structural instability under extreme conditions limits large-scale commercial utilization. Herein, an interface-regulated Ni-rich cathode material LiNi_0.87Co_0.10Al_0.03O₂ with a layer (R3̅m) core, a NiO salt-like (Fm3̅m) phase, and an ultrathin amorphous ion-conductive LiBO₂ (LBO) layer is constructed by gradient boron incorporation and lithium-reactive coating during calcination. The ultrathin LBO layer not only exhausts residual lithium species but also acts as a layer for Li⁺ transport and insulation of detrimental reaction. The NiO salt-like phase in the subsurface could enhance the structural stability of the layer core for the pillar effects. With the positive role provided by the functional hybrid surface layer and boron doping, the modified cathode exhibits enhanced Li⁺ conductivity, structural stability, reversibility of the H2-H3 phase transition, suppressed side reactions, ameliorated transition-metal dissolution, and excellent electrochemical performance. Especially, a 1% wt boron-modified cathode delivers a discharge capacity of 211.99 mA h g^-1 in the potential range of 3.0-4.3 V at 0.2 C and excellent cycle life with a capacity retention of 89.43% after 200 cycles at 1 C.

Multifunctional Integration of Double-Shell Hybrid Nanostructure for Alleviating Surface Degradation of LiNi0.8Co0.1Mn0.1O2 Cathode for Advanced Lithium-Ion Batteries at High Cutoff Voltage

Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode is considered to be among the most promising candidates for high-energy-density lithium-ion batteries (LIBs). However, both capacity fading and structural degradation occur during long-term cycling, which extremely limit the commercial applications of NCM811, especially at a high cutoff voltage (>4.3 V). Here, we design a double-shell hybrid nanostructure consisting of a Li₂SiO₃ coating layer and a cation-mixed layer (Fm3̅m phase) to improve its electrochemical performance. Consequently, the Si-modified NCM811 electrode shows outstanding cycling stability with a 95.2% capacity retention at 4.3 V after 100 cycles and 87.3% at a 4.5 V high cutoff voltage after 100 cycles. This designed double-shell hybrid nanostructure alleviates side reactions, structural degradation, and internal cracking, effectively enhancing the surface structural stability. This efficient strategy provides a valuable step toward further commercial applications of the LiNi_0.8Co_0.1Mn_0.1O₂ cathode and enriches the fundamental understanding of layered cathode materials.

Dual Elements Coupling Effect Induced Modification from the Surface into the Bulk Lattice for Ni-Rich Cathodes with Suppressed Capacity and Voltage Decay

Injection of phase transition from a layered to rock-salt phase into the bulk lattice and side reactions on the interfacial usually causes structure degradation, quick capacity/voltage decay, and even thermal instability. Here, a self-formed interfacial protective layer coupled with lattice tuning was constructed for Ni-rich cathodes by simultaneous incorporation of Zr and Al in a one-step calcination. The migration energy between Zr and Al from the surface into the bulk lattice induces dual modifications from the surface into the bulk lattice, which effectively decrease the formation of cation mixing, the degree of anisotropic lattice change, and the generation of microcracks. With the stabilization role provided by the doped Zr-Al ions and protective function endowed by the surface layer, the modified cathode material exhibits significantly enhanced capacity and voltage retention. Specifically, the capacity retention for the modified cathode material reaches 99% after 100 cycles at 1 C and 25 °C in a voltage range of 3.0-4.3 V, which outperformed that for the pristine cathode (70%). The declination values of the average voltage for the modified cathode are only 0.025 and 0.097 V after 100 cycles at 1 C in voltage ranges of 3.0-4.3 and 2.8-4.5 V, respectively, which are much lower than those for the pristine cathode (0.230 and 0.405 V). The synchronous accomplishment of modification from the surface into the bulk lattice for Ni-rich materials with multiple elements in a one-step calcination process would provide some referenced value for the preparation of other cathode materials.

High-Rate Structure-Gradient Ni-Rich Cathode Material for Lithium-Ion Batteries

To simultaneously achieve high compaction density and superior rate performance, a structure-gradient LiNi_0.8Co_0.1Mn_0.1O₂ cathode material composed by a compacted core and an active-plane-exposing shell was designed and synthesized via a secondary co-precipitation method successfully. The tight stacking of primary particles in the core part ensures high compaction density of the material, whereas the exposed active planes, resulting from the stacking of primary nanosheets along the [001] crystal axis predominantly, in the shell region afford enhanced Li⁺ transport. Thus, this structure-gradient Ni-rich cathode material shows a high compaction density with excellent electrochemical performances, especially the rate performance, exhibiting excellent rate capability (160 mA h g^-1 at 10 C), which is 62% larger than that of the pristine material within 2.75-4.3 V (vs Li⁺/Li). Our work proposes a possible strategy for designing and synthesizing layered cathode materials with the required hierarchical structure to meet different application requirements.

Enhanced Cyclability and High-Rate Capability of LiNi0.88Co0.095Mn0.025O2 Cathodes by Homogeneous Al3+ Doping

To suppress capacity fading of nickel-rich materials for lithium-ion batteries, a homogeneous Al³⁺ doping strategy is realized through tailoring the Al³⁺ diffusion path from the bulk surface to interior. Specifically, the layered LiNi_0.88Co_0.095Mn_0.025O₂ cathode with the radial arrangement of primary grains is successfully synthesized through optimization design of precursors. The Al³⁺ follows the radially oriented primary grains into the bulk by introduction of nano-Al₂O₃ during the sintering process, realizing the homogeneous Al³⁺ distribution in the whole material. Particularly, a series of nano-Al₂O₃-modified LiNi_0.88Co_0.095Mn_0.025O₂ are investigated. With the 2% molar weight of Al³⁺ doping, the capacity retention ratio of the cathode is tremendously improved from 52.26 to 91.57% at 1 C rate after 150 cycles. Even at a heavy current density of 5 (&10) C for the LiNi_0.88Co_0.095Mn_0.025O₂-Al_2% cathode, a high reversible capacity of 172.3 (&165.7) mA h g^-1 can be acquired, which amount to the 84.46 (&81.25) % capacity retention at 0.2 C. Moreover, voltage deterioration is significantly suppressed by homogeneous Al³⁺ doping from the results of median voltage and dQ/dV curves. Therefore, homogeneous Al³⁺ doping benefited from the radial arrangement of primary grains provides an effective and practical way to prolong lifespan, as well as improves rate performance and voltage stability of nickel-rich ternary materials.

High-Performance Li-Ion Batteries Using Nickel-Rich Lithium Nickel Cobalt Aluminium Oxide-Nanocarbon Core-Shell Cathode: In Operando X-ray Diffraction

Nickel-rich layered, mixed lithium transition-metal oxides have been pursued as a propitious cathode material for the future-generation lithium-ion batteries due to their high energy density and low cost. Nevertheless, acute side reactions between Ni⁴⁺ and carbonate electrolyte lead to poor cycling as well as rate performance, which limits their large-scale applications. Here, core-shell like LiNi_0.8Co_0.15Al_0.05O₂ (NCA)-carbon composite synthesized by a solvent-free mechanofusion method is reported to solve this issue. Such a core-shell structure exhibits a splendid rate as well as stable cycling when compared to the physically blended NCA. In operando X-ray diffraction studies show that both materials experience anisotropic structural change, i.e., stacking c-axis undergoes a gradual expansion followed by an abrupt shrinkage; meanwhile, the a-axis contracts during the charging process and vice versa. Interestingly, the core-shell material displays a significantly high reversible capacity of 91% in the formation cycle at 0.1C and a retention of 84% at 0.5C after 250 cycles, whereas pristine NCA retains 71%. The robust mechanical force assisted dry coating obtained by the mechanofusion method shows improved electrochemical performance and demonstrates its practical feasibility.

A Novel Bifunctional Self-Stabilized Strategy Enabling 4.6 V LiCoO2 with Excellent Long-Term Cyclability and High-Rate Capability

Although the theoretical specific capacity of LiCoO2 is as high as 274 mAh g-1, the superior electrochemical performances of LiCoO2 can be barely achieved due to the issues of severe structure destruction and LiCoO2/electrolyte interface side reactions when the upper cutoff voltage exceeds 4.5 V. Here, a bifunctional self-stabilized strategy involving Al+Ti bulk codoping and gradient surface Mg doping is first proposed to synchronously enhance the high-voltage (4.6 V) performances of LiCoO2. The comodified LiCoO2 (CMLCO) shows an initial discharge capacity of 224.9 mAh g-1 and 78% capacity retention after 200 cycles between 3.0 and 4.6 V. Excitingly, the CMLCO also exhibits a specific capacity of up to 142 mAh g-1 even at 10 C. Moreover, the long-term cyclability of CMLCO/mesocarbon microbeads full cells is also enhanced significantly even at high temperature of 60 °C. The synergistic effects of this bifunctional self-stabilized strategy on structural reversibility and interfacial stability are demonstrated by investigating the phase transitions and interface characteristics of cycled LiCoO2. This work will be a milestone breakthrough in the development of high-voltage LiCoO2. It will also present an instructive contribution for resolving the big structural and interfacial challenges in other high-energy-density rechargeable batteries.

Highly Stabilized Ni-Rich Cathode Material with Mo Induced Epitaxially Grown Nanostructured Hybrid Surface for High-Performance Lithium-Ion Batteries

Capacity fading induced by unstable surface chemical properties and intrinsic structural degradation is a critical challenge for the commercial utilization of Ni-rich cathodes. Here, a highly stabilized Ni-rich cathode with enhanced rate capability and cycling life is constructed by coating the molybdenum compound on the surface of LiNi_0.815Co_0.15Al_0.035O₂ secondary particles. The infused Mo ions in the boundaries not only induce the Li₂MoO₄ layer in the outermost but also form an epitaxially grown outer surface region with a NiO-like phase and an enriched content of Mo⁶⁺ on the bulk phase. The Li₂MoO₄ layer is expected to reduce residential lithium species and promote the Li⁺ transfer kinetics. The transition NiO-like phase, as a pillaring layer, could maintain the integrity of the crystal structure. With the suppressed electrolyte-cathode interfacial side reactions, structure degradation, and intergranular cracking, the modified cathode with 1% Mo exhibits a superior discharge capacity of 140 mAh g^-1 at 10 C, a superior cycling performance with a capacity retention of 95.7% at 5 C after 250 cycles, and a high thermal stability.

Structure and electrochemical performance modulation of a LiNi0.8Co0.1Mn0.1O2 cathode material by anion and cation co-doping for lithium ion batteries

Ni-rich layered transition metal oxides show great energy density but suffer poor thermal stability and inferior cycling performance, which limit their practical application. In this work, a minor content of Co and B were co-doped into the crystal of a Ni-rich cathode (LiNi_0.8Co_0.1Mn_0.1O₂) using cobalt acetate and boric acid as dopants. The results analyzed by XRD, TEM, XPS and SEM reveal that the modified sample shows a reduced energy barrier for Li⁺ insertion/extraction and alleviated Li⁺/Ni²⁺ cation mixing. With the doping of B and Co, corresponding enhanced cycle stability was achieved with a high capacity retention of 86.1% at 1.0C after 300 cycles in the range of 2.7 and 4.3 V at 25 °C, which obviously outperformed the pristine cathode (52.9%). When cycled after 300 cycles at 5C, the material exhibits significantly enhanced cycle stability with a capacity retention of 81.9%. This strategy for the enhancement of the electrochemical performance may provide some guiding significance for the practical application of high nickel content cathodes.

Ni-rich layered transition metal oxides show great energy density but suffer poor thermal stability and inferior cycling performance, which limit their practical application.

Combination Effect of Bulk Structure Change and Surface Rearrangement on the Electrochemical Kinetics of LiNi0.80Co0.15Al0.05O2 During Initial Charging Processes

The correlations between bulk/surface structure change and electrochemical kinetics of LiNi_0.80Co_0.15Al_0.05O₂ are systematically investigated at atomic level, including the initial charged, half-charged, and over-charged states. In the initial stage of charge, surface rearrangement occurs and an amorphous Li₂CO₃ layer forms on the surface, which can release stress and provide a stable interface. The Li₂CO₃ surface layer decomposes upon charging, resulting in decreased interface resistance for charge transfer. Meanwhile, the bulk structure goes through the two-phase reaction region toward the solid solution region, which demonstrates higher electrical conductivity and faster Li-ion mobility. Along with the charging process, more substantial surface rearrangement and the decomposed Li₂CO₃ layer lead to surface degradation. Together with the anisotropic volume change-induced mechanical stress, microcracks stem from the surface and provide access for electrolyte penetration. All of these cause high kinetic barriers for Li-ion extraction, as demonstrated by the high interface and charge-transfer resistance and slow lithium diffusion in this region.