Irreversible Phase Transition Research Articles

Enhanced electrochemical performance of O3-type NaNi0.5Mn0.3Co0.2O2 cathodes for sodium-ion batteries via Al-doping

O3-type NaNi0.5Mn0.3Co0.2O2 based positive electrode materials are very promising for sodium-ion batteries. However, the irreversible phase transition due to structural deformation leads to sluggish kinetics, rapid capacity fade, and low C-rate performance, limiting its wide practical applications. The partial substitution of Co3+ (0.545 Å) by Al3+ (0.535 Å) ions in the transition-metal layer in NaNi0.5Mn0.3Co0.2-xAlxO2 (0.01 ≤ x ≤ 0.02) is an effective strategy to address the issue of structural deformation and thus to improve the electrochemical performance of NaNi0.5Mn0.3Co0.2O2 cathode. Solution combustion synthesis of NaNi0.5Mn0.3Co0.2-xAlxO2 (x = 0.01, 0.02) shows O3-type structure of NaNi0.5Mn0.3Co0.2−xAlxO2 material with the space group of R3¯m. The composition with an overall x = 0.02 Al doping delivers an initial 120 mAh g−1 capacity at a 0.1 C rate. It retains 90 % capacity even after 200 cycles than the other stoichiometric aluminum substitution, x = 0.01 (77 %). Moreover, the NaNi0.5Mn0.3Co0.18Al0.02O2 shows a good capacity of ~ 83 mAh g−1 even at a high C-rate of 5 C, almost 70 % of the initial capacity at the 0.1 C rate. The Al-substitute NaNi0.5Mn0.3Co0.2−xAlxO2 cathode's electrochemical performance is attributed to the enhancement in the structural stability of the sodium layered transition metal oxide after the partial substitution of Co3+ by Al3+ ion. Finally, the practical sodium-ion full cells are realized using a hard carbon-based anode and NaNi0.5Mn0.3Co0.18Al0.02O2 cathode, showing 91 % capacity retention at the end of 100th cycles with an OCV of 3.5 V.

Improving the structural reversibility of LiNiO2 by incorporation of Cu, an electrochemical and in-situ XRD study

LiNiO2 is one of the most appealing cathode materials for lithium-ion batteries. However, during electrochemical cycling, irreversible phase transitions occur at high potentials leading to rapid capacity decay. Stopping irreversible structural changes has been achieved by several strategies such as cation doping, solid solution formation, protective coatings, and hybrid strategies. However, no definitive strategy has been envisaged to achieve 100% reversibility. In this work, the effect of incorporating Cu into LNO on the electrochemical performance and structural stability was evaluated by electrochemical and in situ XRD experiments. The structural properties indicate that this material has an ordered crystalline structure with a high degree of cationic ordering, where the presence of Cu3+ was confirmed by XPS. By in situ XRD, it was shown that the Cu-containing LiNiO2 phase is responsible of the charge retention, due to its structural stability during the insertion/deinsertion of Li ions. Furthermore, the presence of Cu, within the LiNiO2 crystalline structure, demonstrated a specific capacity retention of 95%, a high value compared to 45% observed in LiNiO2 after 10 cycles in a potential window of 3.0–4.3 V.

Synthesis of NaNi0.5Mn0.5O2 cathode materials for sodium-ion batteries via spray pyrolysis method

Because of the rich sodium reserves in nature, low cost, and high initial sodium content, O3-NaNi0.5Mn0.5O2 material stands out from other cathode materials. However, O3-NaNi0.5Mn0.5O2 shows poor kinetics and undergoes serious irreversible phase transitions, resulting in structural collapse and deteriorated cyclic performance. Herein, NaNi0.5Mn0.5O2 material with distinguished cyclic and rate performance was prepared via spray pyrolysis combined with a high-temperature solid-phase sintering method, which can deliver a specific capacity of 98.4 mAh g−1 at 1 C between 2.0 and 4.0 V. After 100 cycles, it shows outstanding capacity retention of 89.1 %. Moreover, it can recover 70.4 % of the capacity of 0.1 C even at a high rate of 10 C. This newly proposed synthesis method provides an alternative method to prepare superior electrode materials for sodium-ion batteries.

Single‐crystal spinel Li1.08Mn1.92O4 octahedra cathode covered with Li-ion permeable robust NMC thin-layer protection for high voltage lithium‐ion batteries

An innovative cathode structure consisting of NMC, a Li-ion permeable coating on single crystal (SC) of Li-rich Li1.08Mn1.92O4 (NMC@SC LR-LMO) cathode is reported for first-time as a multifunctional cathode material for Li-ion batteries. The purpose of NMC coating is to protect the active material from acid corrosion while excess Li in LMO crystallite has been added intentionally to increase the structural stability and to mitigate the irreversible phase transitions. At 0.5 C-rate, this NMC@SC LR-LMO cathode vs. Li metal anode provides a stable reversible specific capacity of 115 m Ah g–1 with an energy density of 460 W h kg–1 for 500 cycles. At 60 °C, a stable reversible specific capacity of 113 m Ah g–1 at 0.2 C-rate ensuring energy density of 452 W h kg–1 after 100 cycles is obtained. Full-cell of NMC@SC LR-LMO cathode and MCMB anode exhibit the capacity of 1.23 m Ah cm–2, 95.3% capacity retention even after 100 cycles at 0.44 mA cm–2/ 29.3 m Ah g–1, and the trend is maintained till 500 cycles. Finally, a pouch cell of NMC@SC LR-LMO cathode and MCMB anode of ∼38 m Ah is tested with a reversible areal capacity of 1.27 m Ah cm–2/ 85 m Ah g–1 after 150 cycles.

Strain Engineering by Local Chemistry Manipulation of Triphase Heterostructured Oxide Cathodes to Facilitate Phase Transitions for High‐Performance Sodium‐Ion Batteries

AbstractSodium‐ion oxide cathodes with triphase heterostructures have attracted intensive attention, since the sodium‐storage performance can be enhanced by utilizing the synergistic effect of different phases. However, the composite structures generally suffer from multiple irreversible phase transitions and high lattice strain because of interlayer‐gliding during the charge/discharge process. Here, the concept of strain engineering via manipulating the local chemistry of heterostructured oxide cathode is proposed to regulate the relevant physical and chemical properties, resulting in highly reversible structural evolution (P2/P3/spinel → P2/P3″/spinel) and low intrinsic stress in the potential window of 1.5–4.0 V. Also, the simple structural evolution at a relatively high cut‐off potential of 4.3 V can be detected by in situ X‐ray diffraction and other electrochemical characterization techniques during Na+ extraction/insertion. Meanwhile, the electrode exhibits a high reversible capacity (169.4 mAh g−1 at 0.2 C) and excellent rate performance from 1.5 to 4.3 V. Overall, this study reveals the mechanisms of regulating local chemistry to realize strain engineering of the cathode materials and paves the way for the further improvement of high‐performance sodium‐ion batteries.

Co Substitution of Cationic and Transition Metal in O3-Type NaCrO2 Cathode for High Energy Density

The development of advanced cathode materials with high operating voltage and high reversible capacity is essential to promote the practical realization of sodium ion battery (SIB) technology. Here, O3 type Na0.9Ca0.035Cr0.97Ti0.03O2 is designed by Ca and Ti co-substitution in O3 type NaCrO2, and proposed as a new type of cathode material for high-energy density practical SIBs. On the basis of Chemical science, Alkalin ion successully incorporate NaO6 octahedron of Na0.9Ca0.035Cr0.97Ti0.03O2.1,2 In substitution process two Na+ per single Ca2+, while Cr3+ to Ti4+ ions.3,4 As a result Na+ vacancies are formed Na+ layer. Through co-substitution, structural stability of O3 – Na0.9Ca0.035Cr0.97Ti0.03O2 is increased, because stronger Ti – O bond and immobile Ca2+ ions in Na site synergistically make an effect the unit cell structures. This structural feature suppresses the irreversible phase transition and provide fast Na ion kinetics. In 1.5 – 3.8 voltage range, O3 – Na0.9Ca0.035Cr0.97Ti0.03O2 cathode to deliver the high initial Coulombic efficiency of 95%. Also at a 10 C rate, cathode retains the 90% of its initial capacity after 1000 cycles. In situ X-ray diffraction confirmed the reversible structure properties during charging and discharging process. Moreover, the cathode guarantees the practical applicability with good cycling in a pouch- type full cell using a hard carbon anode, as well as with excellent water durability. References J. J. Braconier, C. Delmas and P. Hagenmuller, Mat. Res. Bull., 1982, 17, 993–1000. J.-Y. Hwang, S.T. Myung and Y.K. Sun, Chem. Soc. Rev., 2017, 46, 3529–3614. L. Zheng, J.C. Bennett and M.N. Obrovac, J. Electrochem. Soc., 2019, 166, A2058–A2064.Y. Tsuchiya, K. Takanashi, T. Nishinobo, T. Ohta and N. Yabuuchi, Chem. Mater., 2016, 28, 7006–7016.

Multifunctional Surface Construction for Long-Term Cycling Stability of Li-Rich Mn-Based Layered Oxide Cathode for Li-Ion Batteries.

Li-rich Mn-based layered oxides (LMLOs) are promising cathode material candidate for the next-generation Li-ion batteries (LIBs) of high energy density. However, the fast capacity fading and voltage decay as well as low Coulombic efficiency caused by irreversible oxygen release and phase transition during the electrochemical process hinder their practical application. To solve these problems, in the present study, a multifunctional surface construction involving a coating layer, spinel-layered heterostructure, and rich-in oxygen vacancies is successfully conducted by a facile thermal reduction of the LMLO particles with potassium borohydride (KBH4 ) as the reducing agent. The multifunctional surface structure plays synergistic effects on suppressing the interface side reaction, reducing the dissolution of transition metal, increasing electron conductivity and lithium diffusion rate. As a result, electrochemical performances of the LMLO cathode are effectively enhanced. With optimization of the addition of KBH4 , the electrode delivers a reversible capacity of 280 mAh g-1 at 0.1 C, which maintains after 100 cycles. The capacity retention with respect to the initial capacity is as high as 98% at 1 C after 400 cycles. The present work provides insights into designing a highly effective functional surface structure of LMLO cathode materials for high-performance LIBs.

Suppression of partially irreversible phase transition in O′3-Na3Ni2SbO6 cathode for sodium-ion batteries by interlayered structural modulation

As a promising cathode material for sodium ion batteries, honeycomb-ordered layered Na3Ni2SbO6 still suffers from rapid capacity fading because of partially irreversible phase transition. Herein, a substitution of Na+ by Rb+ with a larger ionic radius in honeycomb layered Na3−xRbxNi2SbO6 is proposed to modulate the interlayer structure. The results unveil that biphasic transition reversibility of the intermediate P′3 phase is substantially enhanced, and the structure evolution behavior during the charge/discharge process changes due to the structural modulation, which contributes to a suppression of the unfavorable O1 phase and an alleviation of the lattice distortion. Moreover, Rb substituted samples exhibited an improved Na+ (de)intercalation thermodynamics and kinetics. Attributed to the modifications, the sample with optimized Rb content delivers superior cycle stability and rate capacity, demonstrating a feasible strategy for suppressing irreversible phase transition and developing high-performance honeycomb layered materials for sodium ion batteries.

Nitrogen electroreduction deactivation caused by the irreversible conversion of FeS2-SnS2 heterogeneous nanoplates induced by poly(ionic liquids) on polypyrrole/graphene oxide

Through interface and defect engineering, the rich defective FeS2-SnS2 heterogeneous nanoplates have been in-situ grown on poly(1-vinyl-3-ethylimidazole bromide) functionalized polypyrrole/graphene oxide (PVEIB/PPy/GO). The obtained FeS2-SnS2/PVEIB/PPy/GO exhibited the best electrocatalytic performance towards nitrogen reduction reaction (NRR) and the lowest binding energy of Sn 3p, Sn 3d and S 2p orbitals among a series of electrocatalysts prepared by different modifier under the same reaction conditions. Therefore, PVEIB played an important role in the construction of FeS2-SnS2/PVEIB/PPy/GO, resulting in the rich planar defects at the heterointerface of FeS2-SnS2 nanoplates, which was benefit to improve the nitrogen activation capacity. Otherwise, the irreversible phase transitions also occurred after FeS2-SnS2/PVEIB/PPy/GO suffering long term NRR test, eventually resulting in the deactivation of FeS2-SnS2/PVEIB/PPy/GO towards NRR. It will provide a theoretical basis and practical experience for the study of electrocatalyst deactivation based on metal sulfides.

Long-Term Highly Stable High-Voltage LiCoO2 Synthesized via a Solid Sulfur-Assisted One-Pot Approach.

Commercialized lithium cobalt oxide (LCO) only shows a relatively low capacity of ≈175mAhg-1 despite a high theoretical capacity of ≈274mAhg-1 . As an effective and direct strategy, increasing its charge cutoff voltage can, in principle, escalate the capacity, which is however precluded by the irreversible phase transition, oxygen loss, and severe side reactions with electrolytes normally. Herein, an in situ sulfur-assisted solid-state approach is proposed for one-pot synthesis of long-term highly stable high-voltage LCO with a novel compound structure. The coating of coherent spinel Lix Co2 O4 shells on and the gradient doping of SO4 2- polyanions into LCO are in situ realized simultaneously in terms of gas-solid interface reactions between metal oxides and generated SO2 gas from sulfur during synthesis. At 4.6V, this LCO shows the discharge capacities of 232.4mAhg-1 at 0.1C (1C=280mAg-1 ), 215mAhg-1 at 1C and 139mAhg-1 even at 20C and the capacity retentions of 97.4% (89.7%) after 100 (300) cycles at 1C. This approach is facile, low-cost and up-scalable and may provide a route to improve the performance of LCO and other electrode materials greatly.

Entropy and crystal-facet modulation of P2-type layered cathodes for long-lasting sodium-based batteries

P2-type sodium manganese-rich layered oxides are promising cathode candidates for sodium-based batteries because of their appealing cost-effective and capacity features. However, the structural distortion and cationic rearrangement induced by irreversible phase transition and anionic redox reaction at high cell voltage (i.e., >4.0 V) cause sluggish Na-ion kinetics and severe capacity decay. To circumvent these issues, here, we report a strategy to develop P2-type layered cathodes via configurational entropy and ion-diffusion structural tuning. In situ synchrotron X-ray diffraction combined with electrochemical kinetic tests and microstructural characterizations reveal that the entropy-tuned Na0.62Mn0.67Ni0.23Cu0.05Mg0.07Ti0.01O2 (CuMgTi-571) cathode possesses more {010} active facet, improved structural and thermal stability and faster anionic redox kinetics compared to Na0.62Mn0.67Ni0.37O2. When tested in combination with a Na metal anode and a non-aqueous NaClO4-based electrolyte solution in coin cell configuration, the CuMgTi-571-based positive electrode enables an 87% capacity retention after 500 cycles at 120 mA g−1 and about 75% capacity retention after 2000 cycles at 1.2 A g−1.

Stabilizing the Anionic Redox in 4.6 V LiCoO2 Cathode through Adjusting Oxygen Magnetic Moment

AbstractThe irreversible oxygen redox and the resulting structure degradation of LiCoO2 at a high voltage cause very poor cycling performance. Herein, the anionic redox chemistry in 4.6 V LiCoO2 cathode material through manipulating the oxygen magnetic moment (OMM) with oxygen vacancy and V doping is proposed to stabilize, and the relationship between OMM and the oxidation degree of oxygen is revealed. Oxygen vacancy induces the generation of OMM, and the synergy of oxygen vacancy and V doping reduces the change of OMM during charge/discharge processes. This mitigates the oxidation degree of oxygen and improves the reversibility of oxygen redox, which greatly inhibits the irreversible oxygen escape. The oxygen vacancies can further reduce the overlap of the electron clouds and lower the O 2p band center thus decreasing the oxygen redox activity. Moreover, the introduced V also increases the energy barrier of the phase transition and suppresses the irreversible phase transition and Co migration. The irreversible O2 release is significantly inhibited and the cycling stability at 4.6 V is largely enhanced. This study presents the relationship between OMM and the oxidation degree of oxygen and provides some insights into improving the anion redox reversibility through adjusting the oxygen magnetic moment.

In situ co-doping strategy for achieving long-term cycle stability of single-crystal Ni-rich cathodes at high voltage

Single-crystal Ni-rich layered cathode (SC-NCM) is economically appealing for high-energy–density lithium-ion battery but its life span in practical application, especially under high-voltage operation, is significantly hindered by its poor structural instability, irreversible phase transitions, and sluggish electrochemical reaction kinetic. Herein, in-situ zirconium and titanium co-doped single-crystal LiNi0.6Co0.1Mn0.3O2 (Z/T@SC-NCM) material is rationally designed as the structurally and electrochemically stable cathodes for high-energy density batteries. Both the experimental analyses and theoretical calculations reveal that the synergistic effect of Zr/Ti co-doping at transition metal (TM) sites of SC-NCM materials. can not only effectively enhance the Li+ diffusion mobility but also release the internal stress concentration as well as reducing the cationic disordering. As a result, the material-level specific energy of 715 Wh kg−1 is achieved for the single-crystal LiNi0.598Co0.08Mn0.3Zr0.002Ti0.002O2 (Z/T@SC-NCM-0.2) cathode at 2.75–4.6 V with a satisfying capacity retention of 88.5 % after 150 cycles. Impressively, the pouch-type full cell of Zr/Ti@SC-NCM||graphite with a practical area capacity of 4.96 mAh cm−2 delivers an superior capacity retention of 80.6 % after 4000 cycles, which could be expected to extend the battery life-span to more than a decade for electric vehicles. It suggests that engineering the dual-doping in SC-NCM cathodes may provide an effective path toward the low-cost, excellent long-term cycling stability, and high energy density of lithium-ion batteries.

High-Voltage Stabilization of O3-Type Layered Oxide for Sodium-Ion Batteries by Simultaneous Tin Dual Modification.

O3-type layered oxide materials are considered to be a highly suitable cathode for sodium-ion batteries (NIBs) due to their appreciable specific capacity and energy density. However, rapid capacity fading caused by serious structural changes and interfacial degradation hampers their use. A novel Sn-modified O3-type layered NaNi1/3Fe1/3Mn1/3O2 cathode is presented, with improved high-voltage stability through simultaneous bulk Sn doping and surface coating in a scalable one-step process. The bulk substitution of Sn4+ stabilizes the crystal structure by alleviating the irreversible phase transition and lattice structure degradation and increases the observed average voltage. In the meantime, the nanolayer Sn/Na/O composite on the surface effectively inhibits surface parasitic reactions and improves the interfacial stability during cycling. A series of Sn-modified materials are reported. An 8%-Sn-modified NaNi1/3Fe1/3Mn1/3O2 cathode exhibits a doubling in capacity retention increase after 150 cycles in the wide voltage range of 2.0–4.1 V vs Na/Na+ compared to none, and 81% capacity retention is observed after 200 cycles in a full cell vs hard carbon. This work offers a facile process to simultaneously stabilize the bulk structure and interface for the O3-type layered cathodes for sodium-ion batteries and raises the possibility of similar effective strategies to be employed for other energy storage materials.

Ti-substituted O3-type layered oxide cathode material with high-voltage stability for sodium-ion batteries

O3-type layered transition metal oxides (NaxTMO2) have attracted extensive attention as a promising cathode material for sodium-ion batteries because of their high capacity. However, the irreversible phase transition especially cycled under high voltage remains a concerning challenge for NaxTMO2. Herein, a Ti-substituted NaNi0.5Co0.2Mn0.3O2 cathode with strongly suppressed phase transition and enhanced storage stability is investigated. The Ti substitution effectively inhibits the irreversible phase transition and alleviates the structural change even charged to 4.3 V during the repeated Na+ deintercalation process. After storing in air or water, the original O3 phase structure of the material is integrally maintained without the generation of impurity phase. As a result, the as-prepared material shows excellent long-term cycle stability and rate performance when charged to a high voltage of 4.3 V.

Boosting the oxygen evolution reaction performance of wrinkled Mn(OH)2 via conductive activation with a carbon binder

Electrochemical water splitting is one of the most reliable approaches for environmental-friendly hydrogen production. Because of their stability and abundance, Mn-based materials have been studied as electrocatalysts for the oxygen evolution reaction (OER), which is a more sluggish reaction in the water splitting system. To increase the OER activity of Mn, it is imperative to facilitate the structural change of Mn oxide to the active phase with Mn3+ species, known as the active site. Here, we present the relationship between the electronic conductivity in the catalyst layer and the formation of the Mn active phase, δ-MnO2, from wrinkled Mn(OH)2. Mn(OH)2 has poor conductivity, and it disrupts the oxidation reaction toward MnOOH or δ-MnO2. Adjacent conductive carbon to Mn(OH)2 enabled Mn(OH)2 to be oxidized to δ-MnO2. Furthermore, after repetitive cyclic voltammetry activation, the more conductive environment resulted in a higher density of δ-MnO2 through the irreversible phase transition, and thus it contributes to the improvement of the OER activity.

Regulating Pseudo-Jahn–Teller Effect and Superstructure in Layered Cathode Materials for Reversible Alkali-Ion Intercalation

The Jahn-Teller effect (JTE) is one of the most important determinators of how much stress layered cathode materials undergo during charge and discharge; however, many reports have shown that traces of superstructure exist in pristine layered materials and irreversible phase transitions occur even after eliminating the JTE. A careful consideration of the energy of cationic distortion using a Taylor expansion indicated that second-order JTE (pseudo-JTE) is more widespread than the aforementioned JTE because of the various bonding states that occur between bonding and antibonding molecular orbitals in transition-metal octahedra. As a model case, a P2-type Mn-rich cathode (Na3/4MnO2) was investigated in detail. MnO6 octahedra are well known to undergo either elongation or contraction in a specific direction due to JTE. Here, the substitution of Li for Mn (Na3/4(Li1/4Mn3/4)O2) helped to oxidize Mn3+ to Mn4+ suppressing JTE; however, the MnO6 octahedra remained asymmetric with a clear trace of the superstructure. With various advanced analyses, we disclose the pseudo-JTE as a general reason for the asymmetric distortions of the MnO6 octahedra. These distortions lead to the significant electrochemical degradation of Na3/4Li1/4Mn3/4O2. The suppression of the pseudo-JTE modulates phase transition behaviors during Na intercalation/deintercalation and thereby improves all of the electrochemical properties. The insight obtained by coupling a theoretical background for the pseudo-JTE with verified layered cathode material lattice changes implies that many previous approaches can be rationalized by regulating pseudo-JTE. This suggests that the pseudo-JTE should be thought more important than the well-known JTE for layered cathode materials.

Phase Transition in PVDF-TrFE/Hyperbranched Polyester (90/10) Blend Thin Film During Heating-Cooling Cycle Using FTIR Spectroscopy

In this paper, we prepared two spun-cast PVDF-TrFE/hyperbranched polyester (HBP) blend (90/10 wt.-%) film samples on KBr substrate (Blend-AC sample). One of the AC sample was thermally treated at 130oC (Blend-AN sample). Crystal transition behavior were studied by treating both AC and AN samples to 30→120→30oC cycle by in-situ FTIR spectroscopy under transmission (TS) mode. From qualitative FTIR data, absorption intensity of A1 band at 1289.5 cm-1 for AC and 1292 cm-1 for AN decreased gradually during heating for both the samples. However, it is increased at 30oC condition for AC sample, whereas it reached the initial intensity for AN sample at 30oC condition. Blend-AC and Blend-AN thin film samples exhibit irreversible and reversible phase transitions, respectively. Further, the FTIR-TS heating-cooling data were subjected to Factor Analysis (FA). AN sample exhibited reversible phase transition (70%↔70%), while AC sample displayed irreversible transition (50%↔70%), which signifies the importance of this study.

Polymorphism and sodium-ion conductivity of NaTa2PO8 synthesized via the Li+/Na+ ion-exchange reaction of LiTa2PO8

Ion exchange reaction is a promising method to explore metastable compounds that could not be synthesized by conventional high-temperature solid-phase reactions. Herein, a new sodium tantalum phosphate, NaTa2PO8 was synthesized via the Li+/Na+ ion-exchange reaction of the parent compound, LiTa2PO8 in molten NaNO3 medium. NaTa2PO8 underwent an irreversible phase transition from the low- (LT-NaTa2PO8) to the high-temperature polymorph (HT-NaTa2PO8) at approximately 1000 °C. The crystal structures were solved using an ab initio structural determination method based on synchrotron X-ray powder diffraction data. The LT-NaTa2PO8 presented an orthorhombic structure, closely related to that of the parent LiTa2PO8 structure. In contrast, the HT-NaTa2PO8 was found to adopt a monoclinic structure, belonging to a family of monophosphate tungsten bronzes with pentagonal tunnels. The ionic conductivities of LT-NaTa2PO8 (σ = 5 × 10−5 S/cm at 309 °C) and HT-NaTa2PO8 (σ = 2 × 10−7 S/cm at 300 °C) exhibited Arrhenius behavior with activation energies of 0.49 and 0.79 eV, respectively. Bond valence energy landscape (BVEL) calculations indicated that a three-dimensional (3D) conduction pathway is formed in LT-NaTa2PO8 structure, while the conduction pathway in HT-NaTa2PO8 shows a two-dimensional (2D) character.

New insight on correlation between the electrochemical stability and the thermal stability of high nickel cathode materials

Cycle stability and thermal safety are critical to the commercialization of nickel-rich layered materials, yet whether there is a potential correlation between these two factors is still controversial. Herein, the relationship between the cycle stability and thermal stability of nickel-rich cathode materials have been systematically studied through five different calcination temperatures of Li[Ni0.83Co0.12Mn0.05]O2 (NCM83) cathode materials. The research results confirm that the cycle stability and thermal safety of nickel-rich cathode materials do not necessarily show a positive correlation. Actually, with the calcination temperature elevated, the thermal stability of the NCM83 is enhanced, while the cycle stability is degraded. This opposite correlation is not commonly reported in previous literatures. In this work, systematical characterizations demonstrate that under the experimental conditions, the capacity retention of NCM83 is mainly determined by the Li/Ni cation disorder and H2-H3 irreversible phase transition, which is optimal at lower calcination temperature. Meanwhile, the thermal stability is mainly impacted by thermal expansion characteristics and interfacial stability of cathode material, and it is dramatically improved by the mechanical strength of the secondary particles reinforced at high calcinated temperature. This study provides some new insights on understanding and designing of the high-energy cathode materials with long cycle-life and superior safety.