Stabilized Co3+/Co4+ Redox Pair in In Situ Produced CoSe2−x‐Derived Cobalt Oxides for Alkaline Zn Batteries with 10 000‐Cycle Lifespan and 1.9‐V Voltage Plateau

In aqueous alkaline Zn batteries (AZBs), the Co³⁺/Co⁴⁺ redox pair offers a higher voltage plateau than its Co²⁺/Co³⁺ counterpart. However, related studies are scarce, due to two challenges: the Co³⁺/Co⁴⁺ redox pair is more difficult to activate than Co²⁺/Co³⁺; once activated, the Co³⁺/Co⁴⁺ redox pair is unstable, owing to the rapid reduction of surplus Co³⁺ to Co²⁺. Herein, CoSe_2?x is employed as a cathode material in AZBs. Electrochemical analysis recognizes the principal contributions of the Co³⁺/Co⁴⁺ redox pair to the capacity and voltage plateau. Mechanistic studies reveal that CoSe_2?x initially undergoes a phase transformation to derived Co_xO_ySe_z, which has not been observed in other Zn//cobalt oxide batteries. The Se doping effect is conducive to sustaining abundant and stable Co³⁺ species in Co_xO_ySe_z. As a result, the battery achieves a 10 000‐cycle ultralong lifespan with 0.02% cycle^?1 capacity decay, a 1.9‐V voltage plateau, and an immense areal specific capacity compared to its low‐valence oxide counterparts. When used in a quasi‐solid‐state electrolyte, as‐assembled AZB delivers 4200 cycles and excellent tailorability, a promising result for wearable applications. The presented effective strategy for obtaining long‐cyclability cathodes via a phase transformation‐induced heteroatom doping effect may promote high‐valence metal species mediation toward highly stable electrodes.     

High Capacity and High‐Rate NASICON‐Na3.75V1.25Mn0.75(PO4)3 Cathode for Na‐Ion Batteries via Modulating Electronic and Crystal Structures

Sodium superionic conductor (NASICON) cathodes are attractive for Na‐ion battery applications as they exhibit both high structural stability and high sodium ion mobility. Herein, a comprehensive study is presented on the structural and electrochemical properties of the NASICON‐Na_3+yV_2?yMn_y(PO₄)₃ (0 ≤ y ≤ 1) series. A phase miscibility gap is observed at y = 0.5, defining two solid solution domains with low and high Mn contents. Although, members of each of these domains Na_3.25V_1.75Mn_0.25(PO₄)₃ and Na_3.75V_1.25Mn_0.75(PO₄)₃ reversibly exchange sodium ions with high structural integrity, the activity of the Mn³⁺/Mn²⁺ redox couple is found to be absent and present in the former and latter candidate, respectively. Galvanostatic cycling and rate studies reveal higher capacity and rate capability for the Na_3.75V_1.25Mn_0.75(PO₄)₃ cathode (100 and 89 mA h g^?1 at 1C and 5C rate, respectively) in the Na_3+yV_2?yMn_y(PO₄)₃ series. Such a remarkable performance is attributed to optimum bottleneck size (≈5 Ų) and modulated V‐ and Mn‐redox centers as deduced from Rietveld analysis and DFT calculations, respectively. This study shows how important it is to manipulate electronic and crystal structures to achieve high‐performance NASICON cathodes.     

Layered Na‐Ion Cathodes with Outstanding Performance Resulting from the Synergetic Effect of Mixed P‐ and O‐Type Phases

Herein, the synthesis of new quaternary layered Na‐based oxides of the type Na_xMn_yNi_zFe_0.1Mg_0.1O₂ (0.67≤ x ≤ 1.0; 0.5≤ y ≤ 0.7; 0.1≤ z ≤ 0.3) is described. The synthesis can be tuned to obtain P2‐ and O3‐type as well as mixed P‐/O‐type phases as demonstrated by structural, morphological, and electrochemical properties characterization. Although all materials show good electrochemical performance, the simultaneous presence of the P‐ and O‐type phases is found to have a synergetic effect resulting in outstanding performance of the mixed phase material as a sodium‐ion cathode. The mixed P3/P2/O3‐type material, having an average elemental composition of Na_0.76Mn_0.5Ni_0.3Fe_0.1Mg_0.1O₂, overcomes the specific drawbacks associated with the P2‐ and O3‐type materials, allowing the outstanding electrochemical performance. In detail, the mixed phase material is able to deliver specific discharge capacities of up to 155 mAh g^?1 (18 mA g^?1) in the potential range of 2.0–4.3 V. In the narrower potential range of 2.5–4.3 V the material exhibits high average discharge potential (3.4 V versus Na/Na⁺), exceptional average coulombic efficiencies (>99.9%), and extraordinary capacity retention (90.2% after 601 cycles). The unexplored class of P‐/O‐type mixed phases introduces new perspectives for the development of layered positive electrode materials and powerful Na‐ion batteries.     

From Surface ZrO2 Coating to Bulk Zr Doping by High Temperature Annealing of Nickel‐Rich Lithiated Oxides and Their Enhanced Electrochemical Performance in Lithium Ion Batteries

One of the major hurdles of Ni‐rich cathode materials Li_1+x(Ni_xCo_zMn_z)_wO₂, y > 0.5 for lithium‐ion batteries is their low cycling stability especially for compositions with Ni ≥ 60%, which suffer from severe capacity fading and impedance increase during cycling at elevated temperatures (e.g., 45 °C). Two promising surface and structural modifications of these materials to alleviate the above drawback are (1) coatings by electrochemically inert inorganic compounds (e.g., ZrO₂) or (2) lattice doping by cations like Zr⁴⁺, Al³⁺, Mg²⁺, etc. This paper demonstrates the enhanced electrochemical behavior of Ni‐rich material LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) coated with a thin ZrO₂ layer. The coating is produced by an easy and scalable wet chemical approach followed by annealing the material at ≥700 °C under oxygen that results in Zr doping. It is established that some ZrO₂ remains even after annealing at ≥800 °C as a surface layer on NCM811. The main finding of this work is the enhanced cycling stability and lower impedance of the coated/doped NCM811 that can be attributed to a synergetic effect of the ZrO₂ coating in combination with a zirconium doping.     

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.     

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.     

Additional Sodium Insertion into Polyanionic Cathodes for Higher‐Energy Na‐Ion Batteries

Na‐ion technology is increasingly studied as a low‐cost solution for grid storage applications. Many positive electrode materials have been reported, mainly among layered oxides and polyanionic compounds. The vanadium oxy/flurophosphate solid solution Na₃V₂(PO₄)₂F_3‐y O_2y (0 ≤ y ≤ 1), in particular, has proven the ability to deliver ≈500 Wh kg^‐1, operating on the V³⁺/V⁴⁺ (y = 0) or V⁴⁺/V⁵⁺ redox couples (y = 1). This paper reports here on a significant increase in specific energy by enabling sodium insertion into Na₃V₂(PO₄)₂FO₂ to reach Na₄V₂(PO₄)₂FO₂ upon discharge. This occurs at ≈1.6 V and increases the theoretical specific energy to 600 Wh kg^?1, rivaling that of several Li‐ion battery cathodes. This improvement is achieved by the judicious modification of the composition either as O for F substitution, or Al for V substitution, both of which disrupt Na‐ion ordering and thereby enable insertion of the 4th Na. This paper furthermore shows from operando X‐Ray Diffraction (XRD) that this energy is obtained in the cycling range Na₄V₂(PO₄)₂FO₂–NaV₂(PO₄)₂FO₂ with a very small overall volume change of 1.7%, which is one of the smallest volume changes for Na‐ion cathodes and which is a crucial requisite for stable long‐term cycling.     

Microstructure‐Controlled Ni‐Rich Cathode Material by Microscale Compositional Partition for Next‐Generation Electric Vehicles

A multicompositional particulate Li[Ni_0.9Co_0.05Mn_0.05]O₂ cathode in which Li[Ni_0.94Co_0.038Mn_0.022]O₂ at the particle center is encapsulated by a 1.5 µm thick concentration gradient (CG) shell with the outermost surface composition Li[Ni_0.841Co_0.077Mn_0.082]O₂ is synthesized using a differential coprecipitation process. The microscale compositional partitioning at the particle level combined with the radial texturing of the refined primary particles in the CG shell layer protracts the detrimental H2 → H3 phase transition, causing sharp changes in the unit cell dimensions. This protraction, confirmed by in situ X‐ray diffraction and transmission electron microscopy, allows effective dissipation of the internal strain generated upon the H2 → H3 phase transition, markedly improving cycling performance and thermochemical stability as compared to those of the conventional single‐composition Li[Ni_0.9Co_0.05Mn_0.05]O₂ cathodes. The compositionally partitioned cathode delivers a discharge capacity of 229 mAh g^?1 and exhibits capacity retention of 88% after 1000 cycles in a pouch‐type full cell (compared to 68% for the conventional cathode). Thus, the proposed cathode material provides an opportunity for the rational design and development of a wide range of multifunctional cathodes, especially for Ni‐rich Li[Ni_xCo_yMn_1‐x‐y]O₂ cathodes, by compositionally partitioning the cathode particles and thus optimizing the microstructural response to the internal strain produced in the deeply charged state.     

New Na‐Ion Solid Electrolytes Na4−xSn1−xSbxS4 (0.02 ≤ x ≤ 0.33) for All‐Solid‐State Na‐Ion Batteries

Sulfide Na‐ion solid electrolytes (SEs) are key to enable room‐temperature operable all‐solid‐state Na‐ion batteries that are attractive for large‐scale energy storage applications. To date, few sulfide Na‐ion SEs have been developed and most of the SEs developed contain P and suffer from poor chemical stability. Herein, discovery of a new structural class of tetragonal Na_4?xSn_1?xSb_xS₄ (0.02 ≤ x ≤ 0.33) with space group I4₁/acd is described. The evolution of a new phase, distinctly different from Na₄SnS₄ or Na₃SbS₄, allows fast ionic conduction in 3D pathways (0.2–0.5 mS cm^?1 at 30 °C). Moreover, their excellent air stability and reversible dissolution in water and precipitation are highlighted. Specifically, TiS₂/Na–Sn all‐solid‐state Na‐ion batteries using Na_3.75Sn_0.75Sb_0.25S₄ demonstrates high capacity (201 mA h (g of TiS₂)^?1) with excellent reversibility.     

Tunable white light emission from single‐phased Li2SrSiO4:Dy3+ phosphors by co‐doping with Eu3+

A series of single‐phase full‐color emitting Li₂Sr_1−x−ySiO₄:xDy³⁺,yEu³⁺ phosphors were synthesized by solid‐state reaction and characterized by X‐ray diffraction and photoluminescence analyses. The samples showed emission peaks at 488 nm (blue), 572 nm (yellow), 592 nm (orange) and 617 nm (red) under 393 nm excitation. The photoluminescence excitation spectra, comprising the Eu–O charge transfer band and 4f–4f transition bands of Dy³⁺ and Eu³⁺, range from 200 to 500 nm. The Commission Internationale de I'Eclairage chromaticity coordinates for Li₂Sr_0.98−xSiO₄:0.02Dy³⁺,xEu³⁺ phosphors were simulated. By manipulating Eu³⁺ and Dy³⁺ concentrations, the color points of Li₂Sr_1−x−ySiO₄:xDy³⁺,yEu³⁺ were tuned from the greenish‐white region to white light and eventually to reddish‐white region, demonstrating that a tunable white light can be obtained by Li₂Sr_1−x−ySiO₄:xDy³⁺,yEu³⁺ phosphors. Li₂Sr_0.98−xSiO₄:0.02Dy³⁺, xEu³⁺ can serve as a white‐light‐emitting phosphor for phosphor‐converted light‐emitting diode. Copyright © 2014 John Wiley & Sons, Ltd.     

Ni‐Rich/Co‐Poor Layered Cathode for Automotive Li‐Ion Batteries: Promises and Challenges

To pursue a higher energy density (>300 Wh kg^?1 at the cell level) and a lower cost (<$125 kWh^?1 expected at 2022) of Li‐ion batteries for making electric vehicles (EVs) long range and cost‐competitive with internal combustion engine vehicles, developing Ni‐rich/Co‐poor layered cathode (LiNi_1?x?yCo_xMn_yO₂, x+y ≤ 0.2) is currently one of the most promising strategies because high Ni content is beneficial to high capacity (>200 mAh g^?1) while low Co content is favorable to minimize battery cost. Unfortunately, Ni‐rich cathodes suffer from limited structure stability and electrode/electrolyte interface stability in the charged state, leading to electrode degradation and poor cycling performance. To address these problems, various strategies have been employed such as doping, structural optimization design (e.g., core–shell structure, concentration‐gradient structure, etc.), and surface coating. In this review, five key aspects of Ni‐rich/Co‐poor layered cathode materials are explored: energy density, fast charge capability, service life including cycling life and calendar life, cost and element resources, and safety. This enables a comprehensive analysis of current research advances and challenges from the perspective of both academy and industry to help facilitate practical applications for EVs in the future.     

Suppression of Voltage Decay through Manganese Deactivation and Nickel Redox Buffering in High‐Energy Layered Lithium‐Rich Electrodes

Cobalt‐free layered lithium‐rich nickel manganese oxides, Li[Li_xNi_yMn_1?x?y]O₂ (LLNMO), are promising positive electrode materials for lithium rechargeable batteries because of their high energy density and low materials cost. However, substantial voltage decay is inevitable upon electrochemical cycling, which makes this class of materials less practical. It has been proposed that undesirable voltage decay is linked to irreversible structural rearrangement involving irreversible oxygen loss and cation migration. Herein, the authors demonstrate that the voltage decay of the electrode is correlated to Mn⁴⁺/Mn³⁺ redox activation and subsequent cation disordering, which can be remarkably suppressed via simple compositional tuning to induce the formation of Ni³⁺ in the pristine material. By implementing our new strategy, the Mn⁴⁺/Mn³⁺ reduction is subdued by an alternative redox reaction involving the use of pristine Ni³⁺ as a redox buffer, which has been designed to be widened from Ni³⁺/Ni⁴⁺ to Ni²⁺/Ni⁴⁺, without compensation for the capacity in principle. Negligible change in the voltage profile of modified LLNMO is observed upon extended cycling, and manganese migration into the lithium layer is significantly suppressed. Based on these findings, we propose a general strategy to suppress the voltage decay of Mn‐containing lithium‐rich oxides to achieve long‐lasting high energy density from this class of materials.     

A High‐Energy NASICON‐Type Cathode Material for Na‐Ion Batteries

Over the last decade, Na‐ion batteries have been extensively studied as low‐cost alternatives to Li‐ion batteries for large‐scale grid storage applications; however, the development of high‐energy positive electrodes remains a major challenge. Materials with a polyanionic framework, such as Na superionic conductor (NASICON)‐structured cathodes with formula Na_xM₂(PO₄)₃, have attracted considerable attention because of their stable 3D crystal structure and high operating potential. Herein, a novel NASICON‐type compound, Na₄MnCr(PO₄)₃, is reported as a promising cathode material for Na‐ion batteries that deliver a high specific capacity of 130 mAh g^?1 during discharge utilizing high‐voltage Mn^2+/3+ (3.5 V), Mn^3+/4+ (4.0 V), and Cr^3+/4+ (4.35 V) transition metal redox. In addition, Na₄MnCr(PO₄)₃ exhibits a high rate capability (97 mAh g^?1 at 5 C) and excellent all‐temperature performance. In situ X‐ray diffraction and synchrotron X‐ray diffraction analyses reveal reversible structural evolution for both charge and discharge.     

Chiral superstructures from homochiral Zn2+, Co2+, Fe2+‐2,6‐bis (aryl ethylimine)pyridine complexes

We report the hierarchical supramolecular organization of metallosupramolecular homochiral complexes 1 ‐Λ‐(S,S,S,S)‐M²⁺/ 1 ‐?‐(R,R,R,R)‐M²⁺ and 2 ‐ Λ‐(S,S,S,S)‐M²⁺/ 2 ‐?‐ (R,R,R,R)‐M²⁺ of M²⁺ = Co²⁺, Fe²⁺, Zn²⁺ metal ions with chiral pseudo‐terpyridine‐type ligands: 1‐ (S,S) or 1‐ (R,R) = 2,6‐bis (naphthyl ethylimine)pyridine and 2‐ (S,S) or 2‐ (R,R) = 2,6‐bis (phenyl‐ethylimine)pyridine. Circular dichroism measurements in solution were used to confirm the enantiomeric nature of all twelve complexes. For crystal structures of 1 ‐ Λ‐ (S,S,S,S)‐M²⁺ or 1 ‐?‐ (R,R,R,R)‐M²⁺ complexes, absolute configurations {? (or P), Λ (or M)} were confirmed by refinement of the Flack parameter x: ?0.007 ≤ x ≤ 0.11 for the single crystals of 1 ‐Λ‐(S,S,S,S)‐M²⁺/ 1 ‐?‐ (R,R,R,R)‐M²⁺, 2 ‐ Λ‐ (S,S,S,S)‐Fe²⁺, and 2 ‐?‐ (R,R,R,R)‐Co²⁺.     

Synthesis and luminescent properties of novel BaGd2O4:Eu3+ scintillating phosphor

BaGd_2‐xO₄:xEu³⁺ and Ba_1‐yGd_1.79‐2yEu_0.21Na_3yO₄ phosphors were synthesized at 1300°C in air by conventional solid‐state reaction method. Phosphors were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence excitation (PLE) spectra, photoluminescence (PL) spectra and thermoluminescence (TL) spectra. Optimal PL intensity for BaGd_2‐xO₄:xEu³⁺ and Ba_1‐yGd_1.79‐2yEu_0.21Na_3yO₄ phosphors at 276 nm excitation were found to be x = 0.24 and y = 0.125, respectively. The PL intensity of Eu³⁺ emission could only be enhanced by 1.3 times with incorporation of Na⁺ into the BaGd₂O₄ host. Enhanced luminescence was attributed to the flux effect of Na⁺ ions. However, when BaGd₂O₄:Eu³⁺ phosphors were codoped with Na⁺ ions, the induced defects confirmed by TL spectra impaired the emission intensity of Eu³⁺ ions. Copyright © 2012 John Wiley & Sons, Ltd.     

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 Dual‐Insertion Type Sodium‐Ion Full Cell Based on High‐Quality Ternary‐Metal Prussian Blue Analogs

Prussian blue analogs (PBAs) are especially investigated as superior cathodes for sodium‐ion batteries (SIBs) due to high theoretical capacity (≈170 mA h g^?1) with 2‐Na storage and low cost. However, PBAs suffer poor cyclability due to irreversible phase transition in deep charge/discharge states. PBAs also suffer low crystallinity, with considerable [Fe(CN)₆] vacancies, and coordinated water in crystal frameworks. Presently, a new chelating agent/surfactant coassisted crystallization method is developed to prepare high‐quality (HQ) ternary‐metal Ni_xCo_1?x[Fe(CN)₆] PBAs. By introducing inactive metal Ni to suppress capacity fading caused by excessive lattice distortion, these PBAs have tunable limits on depth of charge/discharge. HQ‐Ni_xCo_1?x[Fe(CN)₆] (x = 0.3) demonstrates the best reversible Na‐storage behavior with a specific capacity of ≈145 mA h g^?1 and a remarkably improved cycle performance, with ≈90% capacity retention over 600 cycles at 5 C. Furthermore, a dual‐insertion full cell on the cathode and NaTi₂(PO₄)₃ anode delivers reversible capacity of ≈110 mA h g^?1 at a current rate of 1.0 C without capacity fading over 300 cycles, showing promise as a high‐performance SIB for large‐scale energy‐storage systems. The ultrastable cyclability achieved in the lab and explained herein is far beyond that of any previously reported PBA‐based full cells.     

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.     

Mn versus Al in Layered Oxide Cathodes in Lithium‐Ion Batteries: A Comprehensive Evaluation on Long‐Term Cyclability

Nickel‐rich layered oxide cathodes with the composition LiNi_1?x?yCo_xMn_yO₂ (NCM, (1?x?y) ≥ 0.6) are under intense scrutiny recently to contend with commercial LiNi_0.8Co_0.15Al_0.05O₂ (NCA) for high‐energy‐density batteries for electric vehicles. However, a comprehensive assessment of their electrochemical durability is currently lacking. Herein, two in‐house cathodes, LiNi_0.8Co_0.15Al_0.05O₂ and LiNi_0.7Co_0.15Mn_0.15O₂, are investigated in a high‐voltage graphite full cell over 1500 charge‐discharge cycles (≈5–10 year service life in vehicles). Despite a lower nickel content, NCM shows more performance deterioration than NCA. Critical underlying degradation processes, including chemical, structural, and mechanical aspects, are analyzed via an arsenal of characterization techniques. Overall, Mn substitution appears far less effective than Al in suppressing active mass dissolution and irreversible phase transitions of the layered oxide cathodes. The active mass dissolution (and crossover) accelerates capacity decline with sustained parasitic reactions on the graphite anode, while the phase transitions are primarily responsible for cell resistance increase and voltage fade. With Al doping, on the other hand, secondary particle pulverization is the more limiting factor for long‐term cyclability compared to Mn. These results establish a fundamental guideline for designing high‐performing Ni‐rich NCM cathodes as a compelling alternative to NCA and other compositions for electric vehicle applications.