Improved Cycling Stability of Li[Ni0.90Co0.05Mn0.05]O2 Through Microstructure Modification by Boron Doping for Li‐Ion Batteries

Boron‐doped Li[Ni_0.90Co_0.05Mn_0.05]O₂ cathodes are synthesized by adding B₂O₃ during the lithiation of the hydroxide precursor. Density functional theory confirms that boron doping at a level as low as 1 mol% alters the surface energies to produce a highly textured microstructure that can partially relieve the intrinsic internal strain generated during the deep charging of Li[Ni_0.90Co_0.05Mn_0.05]O₂. The 1 mol% B‐Li[Ni_0.90Co_0.05Mn_0.05]O₂ cathode thus delivers a discharge capacity of 237 mAh g^?1 at 4.3 V, with an outstanding capacity retention of 91% after 100 cycles at 55 °C, which is 15% higher than that of the undoped Li[Ni_0.90Co_0.05Mn_0.05]O₂ cathode. This proposed synthesis strategy demonstrates that an optimal microstructure exists for extending the cycle life of Ni‐rich Li[Ni_1‐x‐yCo_xMn_y]O₂ cathodes that have an inadequate cycling stability in electric vehicle applications and indicates that an optimal microstructure can be achieved through surface energy modification.     

High‐Capacity Concentration Gradient Li[Ni0.865Co0.120Al0.015]O2 Cathode for Lithium‐Ion Batteries

A Ni‐rich concentration‐gradient Li[Ni_0.865Co_0.120Al_0.015]O₂ (NCA) cathode is prepared with a Ni‐rich core to maximize the discharge capacity and a Co‐rich particle surface to provide structural and chemical stability. Compared to the conventional NCA cathode with a uniform composition, the gradient NCA cathode exhibits improved capacity retention and better thermal stability. Even more remarkably, the gradient NCA cathode maintains 90% of its initial capacity after 100 cycles when cycled at 60 °C, whereas the conventional cathode exhibits poor capacity retention and suffers severe structural deterioration. The superior cycling stability of the gradient NCA cathode largely stemmed from the gradient structure combines with the Co‐rich surface, which provides chemical stability against electrolyte attack and reduces the inherent internal strain observed in all Ni‐rich layered cathodes in their charged state, thus providing structural stability against the repeated anisotropic volume changes during cycling. The high discharge capacity of the proposed gradient NCA cathode extends the driving range of electric vehicles and reduces battery costs. Furthermore, its excellent capacity retention guarantees a long battery life. Therefore, gradient NCA cathodes represent one of the best classes of cathode materials for electric vehicle applications that should satisfy the demands of future electric vehicles.     

Understanding the Degradation Mechanisms of LiNi0.5Co0.2Mn0.3O2 Cathode Material in Lithium Ion Batteries

LiNi_xCo_yMn_zO₂ (NCM, 0 ≤ x,y,z < 1) has become one of the most important cathode materials for next‐generation lithium (Li) ion batteries due to its high capacity and cost effectiveness compared with LiCoO₂. However, the high‐voltage operation of NCM (>4.3 V) required for high capacity is inevitably accompanied by a more rapid capacity fade over numerous cycles. Here, the degradation mechanisms of LiNi_0.5Co_0.2Mn_0.3O₂ are investigated during cycling under various cutoff voltage conditions. The surface lattice structures of LiNi_0.5Co_0.2Mn_0.3O₂ are observed to suffer from an irreversible transformation; the type of transformation depends on the cutoff voltage conditions. The surface of the pristine rhombohedral phase tends to transform into a mixture of spinel and rock salt phases. Moreover, the formation of the rock salt phase is more dominant under a higher voltage operation (≈4.8 V), which is attributable to the highly oxidative environment that triggers the oxygen loss from the surface of the material. The presence of the ionically insulating rock salt phase may result in sluggish kinetics, thus deteriorating the capacity retention. This implies that the prevention of surface structural degradation can provide the means to produce and retain high capacity, as well as stabilize the cycle life of LiNi_0.5Co_0.2Mn_0.3O₂ during high‐voltage operations.     

Radially Oriented Single‐Crystal Primary Nanosheets Enable Ultrahigh Rate and Cycling Properties of LiNi0.8Co0.1Mn0.1O2 Cathode Material for Lithium‐Ion Batteries

Ni‐rich Li[Ni_xCo_yMn_1?x?y]O₂ (x ≥ 0.8) layered oxides are the most promising cathode materials for lithium‐ion batteries due to their high reversible capacity of over 200 mAh g^?1. Unfortunately, the anisotropic properties associated with the α‐NaFeO₂ structured crystal grains result in poor rate capability and insufficient cycle life. To address these issues, a micrometer‐sized Ni‐rich LiNi_0.8Co_0.1Mn_0.1O₂ secondary cathode material consisting of radially aligned single‐crystal primary particles is proposed and synthesized. Concomitant with this unique crystallographic texture, all the exposed surfaces are active {010} facets, and 3D Li⁺ ion diffusion channels penetrate straightforwardly from surface to center, remarkably improving the Li⁺ diffusion coefficient. Moreover, coordinated charge–discharge volume change upon cycling is achieved by the consistent crystal orientation, significantly alleviating the volume‐change‐induced intergrain stress. Accordingly, this material delivers superior reversible capacity (203.4 mAh g^?1 at 3.0–4.3 V) and rate capability (152.7 mAh g^?1 at a current density of 1000 mA g^?1). Further, this structure demonstrates excellent cycling stability without any degradation after 300 cycles. The anisotropic morphology modulation provides a simple, efficient, and scalable way to boost the performance and applicability of Ni‐rich layered oxide cathode materials.     

Mn‐Rich P′2‐Na0.67[Ni0.1Fe0.1Mn0.8]O2 as High‐Energy‐Density and Long‐Life Cathode Material for Sodium‐Ion Batteries

Herein, P′2‐type Na_0.67[Ni_0.1Fe_0.1Mn_0.8]O₂ is introduced as a promising new cathode material for sodium‐ion batteries (SIBs) that exhibits remarkable structural stability during repetitive Na⁺ de/intercalation. The O? Ni? O? Mn? O? Fe? O bond in the octahedra of transition‐metal layers is used to suppress the elongation of the Mn? O bond and to improve the electrochemical activity, leading to the highly reversible Na storage mechanism. A high discharge capacity of ≈220 mAh g^?1 (≈605 Wh kg^?1) is delivered at 0.05 C (13 mAg^?1) with a high reversible capacity of ≈140 mAh g^?1 at 3 C and excellent capacity retention of 80% over 200 cycles. This performance is associated with the reversible P′2–OP4 phase transition and small volume change upon charge and discharge (≈3%). The nature of the sodium storage mechanism in a full cell paired with a hard carbon anode reveals an unexpectedly high energy density of ≈542 Wh kg^?1 at 0.2 C and good capacity retention of ≈81% for 500 cycles at 1 C (260 mAg^?1).     

Lithium/Oxygen Incorporation and Microstructural Evolution during Synthesis of Li‐Rich Layered Li[Li0.2Ni0.2Mn0.6]O2 Oxides

As promising cathode materials, the lithium‐excess 3d‐transition‐metal layered oxides can deliver much higher capacities (>250 mAh g^?1 at 0.1 C) than the current commercial layered oxide materials (≈180 mAh g^?1 at 0.1 C) used in lithium ion batteries. Unfortunately, the original formation mechanism of these layered oxides during synthesis is not completely elucidated, that is, how is lithium and oxygen inserted into the matrix structure of the precursor during lithiation reaction? Here, a promising and practical method, a coprecipitation route followed by a microwave heating process, for controllable synthesis of cobalt‐free lithium‐excess layered compounds is reported. A series of the consistent results unambiguously confirms that oxygen atoms are successively incorporated into the precursor obtained by a coprecipitation process to maintain electroneutrality and to provide the coordination sites for inserted Li ions and transition metal cations via a high‐temperature lithiation. It is found that the electrochemical performances of the cathode materials are strongly related to the phase composition and preparation procedure. The monoclinic layered Li[Li_0.2Ni_0.2Mn_0.6]O₂ cathode materials with state‐of‐the‐art electrochemical performance and comparably high discharge capacities of 171 mAh g^?1 at 10 C are obtained by microwave annealing at 750 °C for 2 h.     

High Performance Na0.5[Ni0.23Fe0.13Mn0.63]O2 Cathode for Sodium‐Ion Batteries

The synthesis of a new layered cathode material, Na_0.5[Ni_0.23Fe_0.13Mn_0.63]O₂, and its characterization in terms of crystalline structure and electrochemical performance in a sodium cell is reported. X‐ray diffraction studies and high resolution scanning electron microscopy images reveal a well‐defined P2‐type layered structure, while the electrochemical tests demonstrate excellent characteristics in terms of high capacity and cycle life. This performance, the low cost, and the environmental compatibility of its component poses Na_0.5[Ni_0.23Fe_0.13Mn_0.63]O₂ to be among the most promising materials for the next generation of sodium‐ion batteries.     

Cobalt‐Free High‐Capacity Ni‐Rich Layered Li[Ni0.9Mn0.1]O2 Cathode

Li[Ni_0.9Co_0.1]O₂ (NC90), Li[Ni_0.9Co_0.05Mn_0.05]O₂ (NCM90), and Li[Ni_0.9Mn_0.1]O₂ (NM90) cathodes are synthesized for the development of a Co‐free high‐energy‐density cathode. NM90 maintains better cycling stability than the two Co‐containing cathodes, particularly under harsh cycling conditions (a discharge capacity of 236 mAh g^?1 with a capacity retention of 88% when cycled at 4.4 V under 30 °C and 93% retention when cycled at 4.3 V under 60 °C after 100 cycles). The reason for the enhanced stability is mainly the ability of NM90 to absorb the strain associated with the abrupt anisotropic lattice contraction/extraction and to suppress the formation of microcracks, in addition to enhanced chemical stability from the increased presence of stable Mn⁴⁺. Although the absence of Co deteriorates the rate capability, this can be overcome as the rate capability of the NM90 approaches that of the NCM90 when cycled at 60 °C. The long‐term cycling stability of NM90 is confirmed in a full cell, demonstrating that it is one of the most promising Co‐free cathodes for high‐energy‐density applications. This study not only provides insight into redefining the role of Mn in a Ni‐rich cathode, it also represents a clear breakthrough in achieving a commercially viable Co‐free Ni‐rich layered cathode.     

MnPO4‐Coated Li(Ni0.4Co0.2Mn0.4)O2 for Lithium(‐Ion) Batteries with Outstanding Cycling Stability and Enhanced Lithiation Kinetics

Herein, the successful synthesis of MnPO₄‐coated LiNi_0.4Co_0.2Mn_0.4O₂ (MP‐NCM) as a lithium battery cathode material is reported. The MnPO₄ coating acts as an ideal protective layer, physically preventing the contact between the NCM active material and the electrolyte and, thus, stabilizing the electrode/electrolyte interface and preventing detrimental side reactions. Additionally, the coating enhances the lithium de‐/intercalation kinetics in terms of the apparent lithium‐ion diffusion coefficient. As a result, MP‐NCM‐based electrodes reveal greatly enhanced C‐rate capability and cycling stability—even under exertive conditions like extended operational potential windows, elevated temperature, and higher active material mass loadings. This superior electrochemical behavior of MP‐NCM compared to as‐synthesized NCM is attributed to the superior stability of the electrode/electrolyte interface and structural integrity when applying a MnPO₄ coating. Employing an ionic liquid as an alternative, intrinsically safer electrolyte system allows for outstanding cycling stabilities in a lithium‐metal battery configuration with a capacity retention of well above 85% after 2000 cycles. Similarly, the implementation in a lithium‐ion cell including a graphite anode provides stable cycling for more than 2000 cycles and an energy and power density of, respectively, 376 Wh kg^?1 and 1841 W kg^?1 on the active material level.     

A New High Power LiNi0.81Co0.1Al0.09O2 Cathode Material for Lithium‐Ion Batteries

Among the various Ni‐based layered oxide systems in the form of LiNi_1‐y‐zCo_yAl_zO₂ (NCA), the compostions between y = 0.1–0.15, z = 0.05 are the most successful and commercialized cathodes used in electric vehicles (EVs) and hybrid electric vehicles (HEVs). However, tremendous research effort has been dedicted to searching for better composition in NCA systems to overcome the limitations of these cathodes, particularly those that arise when they are used use at high discharge/charge rates (>5C) and in high temperature (60 °C) environments. In addition, improving the thermal stability at 4.5 V is also very important in terms of the total amount of heat generated and the onset temperature. Here, a new NCA composition in the form of LiNi_0.81Co_0.1Al_0.09O₂ (y = 0.1, z = 0.09) is reported for the first time. Compared to the LiNi_0.85Co_0.1Al_0.05O₂ cathode, LiNi_0.81Co_0.1Al_0.09O₂ exhibits an excellent rate capability of 155 mAh g^?1 at 10 C with a cut‐off voltage range between 3 and 4.5 V, corresponding to 562 Wh kg^?1 at 24 °C. It additionally provides significantly improved thermal stability and electrochemical performance at the high temperature of 60 °C, with a discharge capacity of 122 mAh g^?1 after 200 cycles with capacity retention of 59%.     

Reducing Capacity and Voltage Decay of Co‐Free Li1.2Ni0.2Mn0.6O2 as Positive Electrode Material for Lithium Batteries Employing an Ionic Liquid‐Based Electrolyte

Lithium‐rich layered oxides (LRLOs) exhibit specific capacities above 250 mAh g^?1, i.e., higher than any of the commercially employed lithium‐ion‐positive electrode materials. Such high capacities result in high specific energies, meeting the tough requirements for electric vehicle applications. However, LRLOs generally suffer from severe capacity and voltage fading, originating from undesired structural transformations during cycling. Herein, the eco‐friendly, cobalt‐free Li_1.2Ni_0.2Mn_0.6O₂ (LRNM), offering a specific energy above 800 Wh kg^?1 at 0.1 C, is investigated in combination with a lithium metal anode and a room temperature ionic liquid‐based electrolyte, i.e., lithium bis(trifluoromethanesulfonyl)imide and N‐butyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide. As evidenced by electrochemical performance and high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and online differential electrochemical mass spectrometry characterization, this electrolyte is capable of suppressing the structural transformation of the positive electrode material, resulting in enhanced cycling stability compared to conventional carbonate‐based electrolytes. Practically, the capacity and voltage fading are significantly limited to only 19% and 3% (i.e., lower than 0.2 mV per cycle), respectively, after 500 cycles. Finally, the beneficial effect of the ionic liquid‐based electrolyte is validated in lithium‐ion cells employing LRNM and Li₄Ti₅O₁₂. These cells achieve a promising capacity retention of 80% after 500 cycles at 1 C.     

P2‐K0.75[Ni1/3Mn2/3]O2 Cathode Material for High Power and Long Life Potassium‐Ion Batteries

Rationally designed P2‐K_0.75[Ni_1/3Mn_2/3]O₂ is introduced as a novel cathode material for potassium‐ion batteries (KIBs). P2‐K_0.75[Ni_1/3Mn_2/3]O₂ cathode material designed through electrochemical ion‐exchange from P2‐Na_2/3[Ni_1/3Mn_2/3]O₂ exhibits satisfactory electrode performances; 110 mAh g^?1 (20 mA g^?1) retaining 86% of capacity for 300 cycles and unexpectedly high reversible capacity of about 91 mAh g^?1 (1400 mA g^?1) with excellent capacity retention of 83% over 500 cycles. According to theoretical and experimental investigations, the overall potassium storage mechanism of P2‐K_0.75[Ni_1/3Mn_2/3]O₂ is revealed to be a single‐phase reaction with small lattice change upon charge and discharge, presenting the Ni^4+/2+ redox couple reaction. Such high power capability is possible through the facile K⁺ migration in the K_0.75[Ni_1/3Mn_2/3]O₂ structure with a low activation barrier energy of ≈210 meV. These findings indicate that P2‐K_0.75[Ni_1/3Mn_2/3]O₂ is a promising candidate cathode material for high‐rate and long‐life KIBs.     

A Li2S‐TiS2‐Electrolyte Composite for Stable Li2S‐Based Lithium–Sulfur Batteries

Li₂S is a fully lithiated sulfur‐based cathode with a high theoretical capacity of 1166 mAh g^?1 that can be coupled with lithium‐free anodes to develop high‐energy‐density lithium–sulfur batteries. Although various approaches have been pursued to obtain a high‐performance Li₂S cathode, there are still formidable challenges with it (e.g., low conductivity, high overpotential, and irreversible polysulfide diffusion) and associated fabrication processes (e.g., insufficient Li₂S, excess electrolyte, and low reversible capacity), which have prevented the realization of high electrochemical utilization and stability. Here, a new cathode design composed of a homogeneous Li₂S‐TiS₂‐electrolyte composite that is prepared by a simple two‐step dry/wet‐mixing process is demonstrated, allowing the liquid electrolyte to wet the powder mixture consisting of insulating Li₂S and conductive TiS₂. The close‐contact, three‐phase boundary of this system improves the Li₂S‐activation efficiency and provides fast redox‐reaction kinetics, enabling the Li₂S‐TiS₂‐electrolyte cathode to attain stable cyclability at C/7 to C/3 rates, superior long‐term cyclability over 500 cycles, and promising high‐rate performance up to 1C rate. More importantly, this improved performance results from a cell design attaining a high Li₂S loading of 6 mg cm^?2, a high Li₂S content of 75 wt%, and a low electrolyte/Li₂S ratio of 6.     

Structural and Electrochemical Study of Al2O3 and TiO2 Coated Li1.2Ni0.13Mn0.54Co0.13O2 Cathode Material Using ALD

Nanolayers of Al₂O₃ and TiO₂ coatings were applied to lithium‐ and manganese‐rich cathode powder Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ using an atomic layer deposition (ALD) method. The ALD coatings exhibited different surface morphologies; the Al₂O₃ surface film appeared to be uniform and conformal, while the TiO₂ layers appeared as particulates across the material surface. In a Li‐cell, the Al₂O₃ surface film was stable during repeated charge and discharge, and this improved the cell cycling stability, despite a high surface impedance. The TiO₂ layer was found to be more reactive with Li and formed a Li_xTiO₂ interface, which led to a slight increase in cell capacity. However, the repetitive insertion/extraction process for the Li⁺ ions caused erosion of the surface protective TiO₂ film, which led to degradation in cell performance, particularly at high temperature. For cells comprised of the coated Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ and an anode of meso‐carbon‐micro‐beads (MCMB), the cycling stability introduced by ALD was not enough to overcome the electrochemical instability of MCMB graphite. Therefore, protection of the cathode materials by ALD Al₂O₃ or TiO₂ can address some of the capacity fading issues related to the Li‐rich cathode at room temperature.     

New Class of Ni‐Rich Cathode Materials Li[NixCoyB1−x−y]O2 for Next Lithium Batteries

A new class of layered cathodes, Li[Ni_xCo_yB_1?x?y]O₂ (NCB), is synthesized. The proposed NCB cathodes have a unique microstructure in which elongated primary particles are tightly packed into spherical secondary particles. The cathodes also exhibit a strong crystallographic texture in which the a–b layer planes are aligned along the radial direction, facilitating Li migration. The microstructure, which effectively suppresses the formation of microcracks, improves the cycling stability of the NCB cathodes. The NCB cathode with 1.5 mol% B delivers a discharge capacity of 234 mAh g^?1 at 0.1 C and retains 91.2% of its initial capacity after 100 cycles (compared to values of 229 mAh g^?1 at 0.1 C and 78.8% for pristine Li[Ni_0.9Co_0.1]O₂). This study shows the importance of controlling the microstructure to obtain the required cycling stability, especially for Ni‐rich layered cathodes, where the main cause of capacity fading is related to mechanical strain in their charged state.     

Understanding the Rate Capability of High‐Energy‐Density Li‐Rich Layered Li1.2Ni0.15Co0.1Mn0.55O2 Cathode Materials

The high‐energy‐density, Li‐rich layered materials, i.e., xLiMO₂(1‐x)Li₂MnO₃, are promising candidate cathode materials for electric energy storage in plug‐in hybrid electric vehicles (PHEVs) and electric vehicles (EVs). The relatively low rate capability is one of the major problems that need to be resolved for these materials. To gain insight into the key factors that limit the rate capability, in situ X‐ray absorption spectroscopy (XAS) and X‐ray diffraction (XRD) studies of the cathode material, Li_1.2Ni_0.15Co_0.1Mn_0.55O₂ [0.5Li(Ni_0.375Co_0.25 Mn_0.375)O₂·0.5Li₂MnO₃], are carried out. The partial capacity contributed by different structural components and transition metal elements is elucidated and correlated with local structure changes. The characteristic reaction kinetics for each element are identified using a novel time‐resolved XAS technique. Direct experimental evidence is obtained showing that Mn sites have much poorer reaction kinetics both before and after the initial activation of Li₂MnO₃, compared to Ni and Co. These results indicate that Li₂MnO₃ may be the key component that limits the rate capability of Li‐rich layered materials and provide guidance for designing Li‐rich layered materials with the desired balance of energy density and rate capability for different applications.