Enhanced High‐Rate Cycling Performance of Nickel‐Rich Li[Ni 0.88 Co 0.09 Mn 0.03 ]O 2 Cathodes Through Sc 2 O 3 Doping

LiNiO2 (LNO, 100% Ni) is an old material first identified in the early 1990s (as a higher-capacity and lower-cost alternative to LiCoO2) but has yet to fulfill its potential. Despite intense research efforts for more than two decades, LNO still exhibits rapid capacity loss during cycling and poor thermal stability (1-3). The traditional LNO is generally prepared by solid-state reactions and recognized as Li-deficient Li1-yNi1+yO2 (4). Ex situ characterizations indicated that the performance degradation originates from the detrimental phase transition (layered to rock-salt structure) during electrochemical cycling (5-7), which is closely related to the lattice-oxygen release during charge (8, 9). To improve the performance of LNO, the structure is commonly modified by lattice doping or surface coating, which have led to improved cycle stability but at the cost of capacity loss (10). Meanwhile, these modification approaches failed to address the lattice oxygen instability, as the O2 release was still detected for the doped or surface-coated layered cathodes (11, 12).Here, we demonstrate an Li-enrichment strategy to produce a trigonal-structured layered Li-enriched LNO (Li1.04Ni0.96O2, LR-LNO) with a slight excess of Li to occupy the Ni sites, which is a possible phase according to the Li-Ni-O phase diagram but has never been experimentally synthesized (Figure 1). LR-LNO (Figure 1) enables a combination of a high specific energy density of 904 Wh kg-1, outstanding cyclability (~80% capacity retention after 400 cycles in full cells versus 35 cycles for LNO), and significantly enhanced thermal stability (>70 °C increase in thermal-runaway temperature over LNO).We further designed a double-tilt electrochemical liquid cell inside a transmission electron microscope (TEM) to track the local structural changes at the surface of individual particles during galvanostatic cycling (Figure 2), revealing the performance-enhancing mechanism behind the slight change in the material composition. Excess Li ions in the Ni layer promoted intralayer migration of Ni ions during delithiation in LR-LNO, generating vacancy clusters to trap the electrochemically oxidized molecular O2 in the near-surface lattice. Consequently, the oxygen redox reaction became highly reversible, and the detrimental layered-to-rock-salt phase transition are effectively inhibited, thus improving the structural reversibility of LR-LNO during cycling and the thermal stability.Our results provide a composition fine-tuning strategy to produce highly-reversible cathodes for high energy-density, low-cost and safe batteries. Beyond batteries, the double-tilt operando TEM technique will facilitate studies into complex phase transitions in a wide range of materials. Figure 1 Pristine structure and outstanding performance of LR-LNO References M. M. Thackeray, K. Amine, Layered Li–Ni–Mn–Co oxide cathodes. Nature Energy 6, 933-933 (2021). A. Manthiram, J. B. Goodenough, Layered lithium cobalt oxide cathodes. Nature Energy 6, 323-323 (2021). K. Turcheniuk, D. Bondarev, V. Singhal, G. Yushin, Ten years left to redesign lithium-ion batteries. Nature 559, 467-470 (2018). J.-H. Kim, K.-J. Park, S. J. Kim, C. S. Yoon, Y.-K. Sun, A method of increasing the energy density of layered Ni-rich Li[Ni1−2xCoxMnx]O2 cathodes (x = 0.05, 0.1, 0.2). Journal of Materials Chemistry A 7, 2694-2701 (2019). C. S. Yoon, D.-W. Jun, S.-T. Myung, Y.-K. Sun, Structural stability of LiNiO2 cycled above 4.2 V. ACS Energy Lett. 2, 1150-1155 (2017). D.-W. Jun, C. S. Yoon, U.-H. Kim, Y.-K. Sun, High-energy density core-shell structured Li[Ni0.95Co0.025Mn0.025]O2 cathode for lithium-ion batteries. Chem. Mater. 29, 5048-5052 (2017). C. S. Yoon, M. H. Choi, B. B. Lim, E. J. Lee, Y.-K. Sun, Review—high-capacity Li[Ni1-xCox/2Mnx/2]O2 (x = 0.1, 0.05, 0) cathodes for next-generation Li-ion battery. J. Electrochem. Soc. 162, A2483-A2489 (2015). N. Li et al., Unraveling the cationic and anionic redox reactions in a conventional layered oxide cathode. ACS Energy Lett. 4, 2836-2842 (2019). S. S. Zhang, Problems and their origins of Ni-rich layered oxide cathode materials. Energy Storage Materials 24, 247-254 (2020). M. Bianchini, M. Roca-Ayats, P. Hartmann, T. Brezesinski, J. Janek, There and back again-the journey of LiNiO2 as a cathode active material. Angew. Chem., Int. Ed. 58, 10434-10458 (2019). N. Li et al., Correlating the phase evolution and anionic redox in Co-Free Ni-Rich layered oxide cathodes. Nano Energy 78, (2020). F. Strauss et al., Li2ZrO3-Coated NCM622 for Application in Inorganic Solid-State Batteries: Role of Surface Carbonates in the Cycling Performance. ACS applied materials & interfaces 12, 57146-57154 (2020). Figure 1

Lithium-ion battery is considered to be one of the most promising energy storage systems that are able to satisfy the requirements of power battery, but the current energy density, power density and safety performance for lithium-ion batteries can't meet the needs of the development of electric vehicles. As the only lithium ions supplier, the cathode materials for lithium-ion batteries greatly limit the performance of lithium-ion battery.Therefore, the development of cathode materials with a higher energy density, higher power density and better safety performance is highly desired. Owing to high theoretical capacity, low cost, and low toxicity, ternary layered transition metal oxide cathode materials are considered to be the most promising cathode materials for the next-generation lithium-ion batteries. And in order to fully release the capacities of ternary layered transition metal oxide cathode materials high voltage is necessary, but the cycle stability is not good enough when ternary layered transition metal oxide cathode materials are set with a high voltage range. What’s more, the poor storage performance is another factor that restricts the wide application in electric vehicles. This review describes several common cathode materials, highlighting the advantages and disadvantages of ternary layered transition metal oxide cathode materials and modification progress.

With the advantages of similar theoretical basis to lithium batteries, relatively low budget and the abundance of sodium resources, sodium ion batteries (SIBs) are recognized as the most competitive alternative to lithium‐ion batteries. Among various types of cathodes for SIBs, advantages of high theoretical capacity, nontoxic and facile synthesis are introduced for layered transition metal oxide cathodes and therefore they have attracted huge attention. Nevertheless, layered oxide cathodes suffer from various degradation issues. Among these issues, interface instability including surface residues, phase transitions, loss of active transition metal and oxygen loss takes up the major part of the degradation of layered oxides. These degradation mechanisms usually lead to irreversible structure collapse and cracking generation, which significantly influence the interface stability and electrochemical performance of layered cathodes. This review briefly introduces the background of researches on layered cathodes for SIBs and their basic structure types. Then the origins and effects on layered cathodes of degradation mechanisms are systematically concluded. Finally, we will summarize various interface modification methods including surface engineering, doping modification and electrolyte composition which are aimed to improve interface stability of layered cathodes, perspectives of future research on layered cathodes are mentioned to provide some theoretical proposals.

Spinel LiNi0.5Mn1.5O4 shell enables Ni-rich layered oxide cathode with improved cycling stability and rate capability for high-energy lithium-ion batteries

The demand for high‐performance and cost‐effective lithium‐ion batteries (LIBs) calls for cathodes with high energy density, structural stability, and reduced reliance on costly Co and Ni. Here, a Co‐free and Ni‐minimized (≤10 mol%) Li‐ and Mn‐rich layered oxide cathode is presented, Li 1.2 Mg 0.1 Ni 0.1 Mn 0.6 O 2 , engineered to balance performance and cost. Low‐cost Mg 2+ substitution can stabilizes the lattice and mitigates voltage decay. However, together with Ni minimization, it suppresses the initial oxygen redox, lowering first‐cycle capacity and energy density. Importantly, high‐voltage activation during the initial cycle successfully triggers the latent oxygen redox, and remarkably, enables full capacity recovery in subsequent cycles. This pre‐activation not only restores performance but also mitigates voltage decay and structural degradation over prolonged cycling. The Li 1.2 Mg 0.1 Ni 0.1 Mn 0.6 O 2 delivers a discharge capacity of ≈276.6 mAh g −1 and an energy density of ≈902.2 Wh kg −1 , with ≈93.4% capacity retention after 100 cycles. Operando X‐ray diffraction reveals a minimal c ‐axis variation (≈0.13%) and provides evidence of suppressed structural disorder following pre‐activation. Supported by electrochemical measurements, structural analysis, and first‐principles calculations, these findings unlock a pathway toward cost‐effective, high‐energy layered cathodes with stable cycling performance for next‐generation LIBs.

Surface Stabilization of O3-type Layered Oxide Cathode to Protect the Anode of Sodium Ion Batteries for Superior Lifespan.

Owing to their high theoretical specific capacity and low cost, lithium- and manganese-rich layered oxide (LMR) cathode materials are receiving increasing attention for application in lithium-ion batteries. However, poor lithium ion and electron transport kinetics plus side effects of anion and cation redox reactions hamper power performance and stability of the LMRs. In this study, LMR Li1.2Mn0.6Ni0.2O2 was modified by phosphorus (P)-doping to increase Li+ conductivity in the bulk material. This was achieved by increasing the interlayer spacing of the lithium layer, electron transport and structural stability, resulting in improvement of the rate and safety performance. P5+ doping increased the distance between the (003) crystal planes from ~0.474 nm to 0.488 nm and enhanced the structural stability by forming strong covalent bonds with oxygen atoms, resulting in an improved rate performance (capacity retention from 38% to 50% at 0.05 C to 5 C) and thermal stability (50% heat release compared with pristine material). First-principles calculations showed the P-doping makes the transfer of excited electrons from the valence band to conduction band easier and P can form a strong covalent bond helping to stabilize material structure. Furthermore, the solid-state electrolyte modified P5+ doped LMR showed an improved cycle performance for up to 200 cycles with capacity retention of 90.5% and enhanced initial coulombic efficiency from 68.5% (pristine) or 81.7% (P-doped LMR) to 88.7%.

High Pressure Effect on Structural and Electrochemical Properties of Anionic Redox-Based Lithium Transition Metal Oxides

Ti, F Codoped Sodium Manganate of Layered P2-Na _0.7 MnO _2.05 Cathode for High Capacity and Long-Life Sodium-Ion Battery

Layered lithium nickel oxide (LiNiO2), with a specific charge-storage capacity of almost 250 mA h g-1, an operating voltage of 3.8 V vs. Li+/Li, and a high packing density of above 3.4 g cm-3, offers a very high energy density approaching the limits of layered oxide cathode materials for lithium-ion batteries. However, despite early interests in the community, practical application of LiNiO2 was soon dismissed for a multitude of problems. This includes (i) poor thermal-abuse tolerance triggering battery thermal runaway at high states of charge, and (ii) severely restricted reversible capacity of < 200 mA h g-1 for desired cycle/calendar life owing to a high surface reactivity with conventional ethylene carbonate (EC)-based electrolytes and not fully reversible rhombohedral H2/H3 phase transition at > 4.2 V vs. Li+/Li. In spite of recent efforts on stabilizing ultrahigh-nickel layered oxides (Ni > 0.9) during battery operation through compositional tuning, the poor thermal stability and cyclability over a broad Li content range remain challenges of LiNiO2-based cathodes. Here we design nonaqueous electrolytes with exclusively aprotic acyclic carbonate solvents (such as ethyl methyl carbonate, EMC) tailored to an ultrahigh-nickel layered oxide cathode (LiNi0.94Co0.06O2). Common lithium-conducting salts (e.g., lithium hexafluorophosphate, LiPF6) and interphase-forming additives (e.g., vinylene carbonate, VC) are adopted in two model electrolyte systems. Assembled graphite|LiNi0.94Co0.06O2 pouch-type full cells in the two EC-free electrolyte systems show excellent long-term cycling performance of ~ 80% capacity retention after 1,000 charge-discharge cycles at 25 oC (1C, 2.5 – 4.2 V), notably superior to the same cells in the baseline EC-containing electrolyte (1.0 M LiPF6/EC-EMC(3:7)+2%VC). Through time-of-flight secondary-ion mass spectrometry coupled with lithium isotopic labelling and in situ X-ray diffraction, we demonstrate suppressed unwanted electrode-electrolyte reactions and irreversible structural degradation of LiNi0.94Co0.06O2 at highly delithiated states in the EC-free electrolytes during battery operation. In addition, through differential scanning calorimetry, we also show significantly inhibited self-heating of the ultrahigh-Ni layered oxide cathode at full charge in the EC-free electrolytes, outperforming charged LiNi0.8Co0.15Al0.05O2 in the EC-containing electrolyte. In summary, we present a facile approach of nonaqueous EC-free electrolytes to address the long-standing challenges of LiNiO2-based cathode materials for safer and long-life high-energy-density lithium-ion batteries.

Polycrystalline secondary particle size regulation boosts the cycle performance of ultra-high-nickel layered oxide cathode materials

Ni‐rich layered oxide cathodes are an immediately applicable alternative for meeting the high energy density demand of lithium‐ion batteries. The most significant hurdle of Ni‐rich layered cathode materials is their poor cyclability because of their increasing surface resistance due to their electrochemically reactive surfaces causing side reactions and the occurrence of Li/Ni cation mixing. Surface coating has been extensively studied for safeguarding particles, thereby leading to increases in electrochemical performance; however, the synthesis conditions must be carefully controlled due to the fragile surface of a Ni‐rich layered cathode. Herein, an effective coating method with self‐assembled ZrO2 (SA–ZrO2) on the surface of a Ni‐rich layered cathode material, LiNi0.82Co0.09Mn0.09O2 (NCM82), through a low‐temperature self‐combustion reaction is proposed. SA–ZrO2 is built by a combustion reaction of Zr(SO4)2·4H2O and thioacetamide to improve the surface stability of the cathode. In addition, a very small content of SOx is retained from the precursor, which promotes high lithium diffusion on the surface. Systematic analyses by X‐ray photoelectron spectroscopy and transmission electron microscopy demonstrate that this highly homogeneous ZrO2 coating layer, which is prepared at a low temperature of 500 °C, largely enhances the electrochemical performance in the half‐cell and full‐cell.

Building a stable cathode-electrolyte interface (CEI) is crucial for achieving high-performance layered metal oxide cathode materials LiNixCoyMn1-x-yO2 (NCM). In this work, a novel 4-fluorobenzene isocyanate (4-FBC) electrolyte additive that contains isocyanate and benzene ring functional groups is proposed, which can form robust and homogeneous N-rich and benzene ring skeleton CEI film on the cathode surface, leading to significant improvement in the electrochemical performance of lithium-ion batteries. Taking LiNi0.5Co0.2Mn0.3O2 (NCM523) as an example, the NCM523/SiO@Graphite pouch full cells with electrolytes containing a mass fraction of 1% 4-FBC additives demonstrate improved capacity retention after 200 cycles, retaining capacity retention rates of 81.3%, which is much higher than that of 39.1% without additive. The improvement can be ascribed to the mitigation of electrolyte decomposition and inhibition of transition metal ions the dissolution from the cathode material due to the stable CEI film. Moreover, the electrochemical performance enhancement can also be achieved in high voltage and Ni-rich cathode materials, indicating the universality and effectiveness of this strategy for the practical applications of high energy density lithium-ion batteries.

Lithium-ion batteries have become the choice of power source for portable electronics and electric vehicles as they offer higher energy density than other rechargeable systems. They are also being intensively pursued for grid storage of electricity produced from renewable sources like solar and wind. Cost, safety, cycle life, energy, power, and environmental impact are the major factors in adopting them for a specific application. Among the various practically viable insertion-compound cathode chemistries available, the layered LiMO2 (M = Mn, Ni, Co, and their solid solutions) oxides offer the highest energy density. Accordingly, there is immense interest in both academia and industry in increasing the charge-storage capacities of the layered oxide cathodes beyond the current levels. In this regard, layered oxide cathode compositions with higher nickel contents (> 50 %) are drawing much attention in recent years since Ni offers higher capacity than Co as Ni3+ can be oxidized fully to Ni4+ without releasing oxygen from the lattice unlike Co3+, which can be oxidized only to ~ 3.5+ to avoid oxygen release from the lattice. Unfortunately, compositions with high Ni contents suffer from (i) multiple phase transitions, resulting in volume change and internal stress and (ii) high surface reactivity with the organic liquid electrolyte, resulting in a growth of cell impedance and fast capacity fade during cycling. They also suffer from high surface reactivity with ambient air to form lithium hydroxide and lithium carbonate on the particle surface, which not only degrades the electrochemical performance but also severely hampers the electrode fabrication process. Innovative approaches to overcome the above challenges are needed to employ high-nickel layered oxide cathodes in practical lithium-ion cells. This presentation will focus first on developing a fundamental understanding of the factors that control the capacity fade and air-reactivity of high-nickel layered oxide cathodes, employing samples with secondary particle sizes of ~ 10 microns and advanced bulk and surface characterization methodologies. In-depth understanding obtained with high-nickel layered oxide cathodes with Ni contents of as high as 94% and graphite anodes retrieved from full cells before and after 1,000 – 3,000 cycles based on a combination of characterization techniques, viz., X-ray photoelectron spectroscopy (XPS), time-of-flight – secondary ion mass spectroscopy (TOF-SIMS), and high-resolution transmission electron microscopy (TEM), will be presented. Utilizing the understanding gained, the presentation will then focus on the design and development of layered oxide compositions with controlled bulk and surface structures as well as new electrolytes that offer a robust interface with both the graphite anode and high-nickel layered oxide cathodes will be presented. Viability to realize lithium-ion cells with cathode capacities of as high as ~ 220 mAh/g, high power capability, and high volumetric energy density will be discussed.

Enhancing the energy density of layered oxide cathode materials is of great significance for realizing high-performance sodium-ion batteries and promoting their commercial application. Lattice oxygen redox at high voltage usually enables a high capacity and energy density. But the structural degradation, severe voltage decay, and the resultant poor cycling performance caused by irreversible oxygen release seriously restrict the practical application. Herein we introduce a novel fence-type superstructure (2a×3a type supercell) into O3-type layered cathode material Na0.9Li0.1Ni0.3Mn0.3Ti0.3O2 and achieve a stable cycling performance at a high voltage of 4.4 V. The fence-type superstructure effectively inhibits the formation of the vacancy clusters resulting from out-of-plane Li migration and in-plane transition metal migration at high voltage due to the wide d-spacing, thereby significantly reducing the irreversible release of lattice oxygen and greatly stabilizing the crystal structure. The cathode exhibits a high energy density of 545 Wh kg-1, a high rate capability (112.8 mAh g-1 at 5 C) and a high cycling stability (85.8 %@200 cycles with a high initial capacity of 148.6 mAh g-1 at 1 C) accompanied by negligible voltage attenuation (98.5 %@200 cycles). This strategy provides a distinct spacing effect of superstructure to design stable high-voltage layered cathode materials for Na-ion batteries.