Nickel-rich Cathode Materials Research Articles

Comparison of structural and electrochemical properties of LiNi0.8Co0.15Al0.05O2 with Li site doping by different cations

Nickel-rich cathode materials are widely used for electronic devices because of their high capacity and rate performance. However, structural deterioration after long-term cycling leads to a significant decline in capacity and cycle life. In this work, the effects of three different cations doping on the structural stability and electrochemical performance of Ni-rich cathode materials were investigated. XRD characterization reveals that doped cation leads to broadening of the distance between Li layers and inhibiting Li+/Ni2+ mixing arrangement. Compared with Na+ and K+, the high valence Mg2+ provides a stronger Mg-O bond, which can effectively restrain the undesired phase transition and sustain the ordered structure. Electrochemical tests demonstrate that NCA with Mg doping has better cycle stability and rate performance than Na and K. The capacity retention rate of NCA with 1% Mg doping is 87.7% after 200 cycles at 1C, and it can still provide a specific capacity of 146.8 mAh g−1 at a high rate of 5C.

Improving High-Temperature Cycle Stability and Rate Performance of LiNi0.82Co0.11Mn0.07O2 Cathode Materials Using Hydrogen Peroxide Solution Washing System

In this study, for the removal of residual lithium (Li2CO3,LiOH) from a nickel-rich cathode material surface, LiNi0.82Co0.11Mn0.07O2 cathode materials were washed with an aqueous solution of hydrogen peroxide (H2O2).H2O2 ( pH6.04), a weak acid, can easily decompose Li2CO3 and LiOH as an oxidizing agent. On titration of residual lithium, the amounts of LiOH and Li2CO3 are 390 and 605ppm,25 - and 47 -times lower, after H2O2 washing compared to 10,296 and 28,440ppm, respectively, in case of cathode materials before washing. On DSC thermal analysis, the peak temperature and calorific value of the cathode material washed with H2O2 were 245.5∘C and 602.0 J/g, respectively, whereas the bare case was 208.6∘C and 1,071 J/g, respectively. Therefore, H2O2-washed LiNi0.82Co0.11Mn0.07O2 cathode materials had higher capacity heat retention after 100 cycles at 55∘C(85.6% at 0.5C) than the bare LiNi0.82Co0.11Mn0.07O2 cathode materials (78.6% at 0.5C).

Recovery of Degraded Ni-Rich NMC811 Particles for Lithium-Ion Batteries

Nickel-rich cathode materials attract a lot of attention due to their high energy density. However, their sensitivity to air and moisture hinders their practical applications. Exposing Ni-rich NMC in the air will produce by-products that are not conducive to lithium-ion transmission. Water washing can be used to remove by-products on the surface, but it can also introduce new problems, such as the generation of NiO on the particle surface, which will reduce the electrochemical performance of the material. In this study, Al2O3 atomic layer deposition (ALD) was applied on degraded NMC811 particles to recover the electrochemical performance of the degraded NMC811 particles, which had been exposed to moisture. XPS and XRD analysis verified that the Al2O3 ALD coating removed the contaminant components on the particle surface, such as LiOH and Li2CO3, as well as reactivation of inactive Ni due to reaction with moisture. Furthermore, the coating film can also inhibit side reactions during the charge and discharge process and enhance the cycling stability.

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.

Multi-Role Surface Modification of Single-Crystalline Nickel-Rich Lithium Nickel Cobalt Manganese Oxides Cathodes with WO3 to Improve Performance for Lithium-Ion Batteries

Compared with the polycrystalline system, the single-crystalline ternary cathode material has better cycle stability because the only primary particles without grain boundaries effectively alleviate the formation of micro/nanocracks and retain better structural integrity. Therefore, it has received extensive research attention. There is no consistent result whether tungsten oxide acts as doping and/or coating from the surface modification of the polycrystalline system. Meanwhile, there is no report on the surface modification of the single-crystalline system by tungsten oxide. In this paper, multirole surface modification of single-crystalline nickel-rich ternary cathode material LiNi0.6Co0.2Mn0.2O2 by WO3 is studied by a simple method of adding WO3 followed by calcination. The results show that with the change in the amount of WO3 added, single-crystalline nickel-rich ternary cathode material can be separately doped, separately coated, and both doped and coated. Either doping or coating effectively enhances the structural stability, reduces the polarization of the material, and improves the lithium-ion diffusion kinetics, thus improving the cycle stability and rate performance of the battery. Interestingly, both doping and coating (for SC-NCM622-0.5%WO3) do not show a more excellent synergistic effect, while the single coating (for SC-NCM622-1.0%WO3) after eliminating the rock-salt phase layer performs the most excellent modification effect.

Mg,Ti-base surface integrated layer and bulk doping to suppress lattice oxygen evolution of Ni-rich cathode material at a high cut-off voltage

The Nickel-rich layered cathode materials charged to 4.5 V can obtain a specific capacity of more than 200 mAh g−1. However, the nickel-rich layered cathode materials suffer from the severe capacity fade during high-voltage cycling, which is related to the phase transformation and the surface sides reactions caused by the lattice oxygen evolution. Here, the simultaneous construction of a Mg, Ti-based surface integrated layer and bulk doping through Mg, Ti surface treatment could suppress the lattice oxygen evolution of Ni-rich material at deep charging. More importantly, Mg and Ti are co-doped into the particles surface to form an Mg2TiO4 and Mg0.5–xTi2–y(PO4)3 outer layer with Mg and Ti vacancies. In the constructed surface integrated layer, the reverse electric field in the Mg2TiO4 effectively suppressed the outward migration of the lattice oxygen anions, while Mg0.5–xTi2–y(PO4)3 outer layer with high electronic conductivity and good lithium ion conductor could effectively maintained the stability of the reaction interface during high-voltage cycling. Meanwhile, bulk Mg and Ti co-doping can mitigate the migration of Ni ions in the bulk to keep the stability of transition metal–oxygen (M−O) bond at deep charging. As a result, the NCM@MTP cathode shows excellent long cycle stability at high-voltage charging, which keep high capacity retention of 89.3% and 84.3% at 1C after 200 and 100 cycles under room and elevated temperature of 25 and 55 °C, respectively. This work provides new insights for manipulating the surface chemistry of electrode materials to suppress the lattice oxygen evolution at high charging voltage.

Competitive Doping Chemistry for Nickel-Rich Layered Oxide Cathode Materials.

Chemical modification of electrode materials by heteroatom dopants is crucial for improving storage performance in rechargeable batteries. Electron configurations of different dopants significantly influence the chemical interactions inbetween and the chemical bonding with the host material, yet the underlying mechanism remains unclear. We revealed competitive doping chemistry of Group IIIA elements (boron and aluminum) taking nickel-rich cathode materials as a model. A notable difference between the atomic radii of B and Al accounts for different spatial configurations of the hybridized orbital in bonding with lattice oxygen. Density functional theory calculations reveal, Al is preferentially bonded to oxygen and vice versa, and shows a much lower diffusion barrier than BIII . In the case of Al-preoccupation, the bulk diffusion of BIII is hindered. In this way, a B-rich surface and Al-rich bulk is formed, which helps to synergistically stabilize the structural evolution and surface chemistry of the cathode.

Dictating the interfacial stability of nickel-rich LiNi0.90Co0.05Mn0.05O2 via a diazacyclo electrolyte additive – 2-Fluoropyrazine

Nickel-rich (Ni-rich) cathode materials, LiNixCoyMnzO2 (NCM, x ≥ 0.9, x + y + z = 1) hold great promise for developing high energy density lithium ion batteries especially for vehicle electrification. However, the practical application of Ni-rich cathode materials is still suffered from fast structural and interfacial degradation, and the resulted capacity decay. In this study, a diazacyclo type electrolyte additive, 2-fluoropyrazine (2-FP), was explored for the first time to boost the interfacial stabilization of single crystal LiNi0.90Co0.05Mn0.05O2 (NCM90) cathode. The capacity retention of the NCM90 is evidently promoted from 72.3% to 82.1% after 200 cycles at 1C (180 mA g−1) when adding 0.2% 2-FP into the electrolyte. The improvement of the electrochemical performance is ascribed to the generation of a compact and homogeneous cathode electrolyte interphase (CEI) film through ring-opening electrochemical polymerization of 2-FP upon the NCM90 electrode particles. This enhanced CEI layer benefits the suppression of the decomposition of LiPF6 electrolyte and the dissolution of the transition metals (Co and Mn), thus preventing the detrimental side reactions between the NCM90 electrode and the electrolyte.

Enhanced structure and electrochemical stability of single crystal nickel-rich cathode material by La2Li0.5Co0.5O4 surface coating

The emergence of single crystal nickel-rich cathode materials preparation offsets the poor cycle performance of traditional ternary cathode materials, with an efficient enhancement of the energy density. Despite all this, the stability of single crystal Ni-rich materials is still hard to fully meet the commercial requirements. We select La and Co elements for co-coating single crystal cathode materials by an efficient method, La2Li0.5Co0.5O4 coating layer with a thickness of about 5 nm is successfully formed on the single crystal nickel-rich samples. The coating layer effectively protect nickel-rich materials from the corrosion of electrolyte and retain a high Li-ion conductivity during charge/discharge processes. Besides, the part of residual lithium reacts with La and Co, forming La2Li0.5Co0.5O4 coating layer, and decorates the materials surface. Eventually, the single crystal NCM811 with 2 wt% La2Li0.5Co0.5O4 coating affords a terrific cyclic stability after 200 cycles. The capacity retention is 81.15% at 1 C with voltage range of 2.8–4.3 V, obtaining an 18% performance improvement compare with that of pristine material. Moreover, the rate performance and first charge/discharge efficiency are improved to a certain extent. The co-coating process with La and Co is a competitive approach to modify the performance of single crystal nickel-rich cathode materials and contribute to the commercial application of the NCM811 materials.

Interfacial Reviving of the Degraded LiNi0.8 Co0.1 Mn0.1 O2 Cathode by LiPO3 Repair Strategy.

Nickel-rich cathode materials, owing to their high energy density and low cost, are considered to be one of the cathodes with the most potential in next-generation lithium-ion batteries. Unfortunately, this kind of cathode with highly active surface is easy to react with H2 O and CO2 when exposed to ambient air, resulting in the formation of lithium impurities and interfacial phase transition as well as deterioration of the electrochemical properties. In this work, the evolution mechanism of the structure and interface of LiNi0.8 Co0.1 Mn0.1 O2 during air-exposure is systematically investigated. Furthermore, a facile reviving strategy is proposed to restore the degraded LiNi0.8 Co0.1 Mn0.1 O2 by using LiPO3 as the repair agent. The lithium impurities on the surface of the degraded sample can transform into the repair/coating layer, and part of the rock salt phase on the subsurface can revive to layered phase after repair heat treatment. As a result, the optimized cathode delivers an initial discharge capacity of 198.3 mAh g-1 at 0.1C and a capacity retention of 85.5% after 50 cycles. Although slightly lower than the bare sample (201 mAh g-1 and 88%), they are obviously higher than the exposed samples (166.5 mAh g-1 and 40.4%). The regenerated electrochemical properties should be attributed to the multifunctional repair layer that can efficiently reduce the surface lithium impurities, prevent the corrosion of electrolyte, and improve the interfacial Li+ diffusion kinetics. This work can effectively reduce the waste of the degraded Ni-rich ternary materials and realize the transformation of "waste" into wealth.

Accelerated synthesis of Li(Ni0.8Co0.1Mn0.1)O2 cathode materials using flame-assisted spray pyrolysis and additives

Nickel-rich cathode materials are promising in lithium-ion battery applications because of their high energy density and low material cost. Unfortunately, reducing the synthesis cost of nickel-rich cathode materials is challenging because of the time-consuming and energy-intensive calcination. Therefore, the current work aims to explore strategies for significantly reducing the calcination time of nickel-rich cathode material Li(Ni0.8Co0.1Mn0.1)O2 (NCM811). We used a flame-assisted spray pyrolysis method to synthesize samples with and without using low-cost urea as an additive. Both in situ thermal X-ray diffraction (XRD) and ex situ XRD revealed that urea addition weakened the sensitivity of crystallization and cation mixing to calcination conditions. As a result, with only 20 min of calcination at 875 °C and without any preheating and ramping steps, the NCM811 sample showed an ordered layered structure and comparable electrochemical performance to those with long-time calcination. Moreover, the current work demonstrated that the shortened post calcination was benefited from lithium-embedded particles that likely improved the uniformity of lithium distribution in as-synthesized powder. Therefore, carefully designing initial lithium distribution in particles prior to calcination could also be a useful strategy for other synthesis methods to shorten high-temperature calcination steps, leading to significant reductions in energy consumption and fabrication cost.

Probing the improved stability for high nickel cathode via dual-element modification in lithium-ion

One of the major hurdles of nickel-rich cathode materials for lithium-ion batteries is the low cycling stability, especially at high temperature and high voltage, originating from severe structural degradation, which makes this class of cathode less practical. Herein, we compared the effect of single and dual ions on electrochemical performance of high nickel (LiNi0.88Mn0.03Co0.09O2, NMC) cathode material in different temperatures and voltage ranges. The addition of a few amounts of tantalum (0.2 wt%) and boron (0.05 wt%) lead to improved electrochemical performance. The co-modified LiNi0.88Mn0.03Co0.09O2 displays an initial discharge capacity of 234.9 mAh/g at 0.1 C and retained 208 mAh/g at 1 C after 100 cycles at 45 °C, which corresponds to a capacity retention of 88.5%, compared to the initial discharge capacity of 234.1 mAh/g and retained capacity of 200.5 mAh/g (85.6%). The enhanced capacity retention is attributed to the synergetic effect of foreign elements by acting as a surface structural stabilizer without sacrificing specific capacity.

A new modification strategy for improving the electrochemical performance of high-nickel cathode material: V2O5 particles anchored on rGO sheets as a dual coating layer

Nickel-rich material has the advantages of high energy density and low cost, so it is an attractive cathode material. However, the defects such as fast capacity drop and low capacity at high rates hinder its commercial application. Herein, to solve the problems and obtain nickel-rich material with high performance, a novel dual conductive layer is designed and coated on the surface of LiNi0.84Co0.11Mn0.05O2 material. The uniform hybrid coating layer is composed of vanadium pentoxide (V2O5) and reduced graphene oxide (rGO). The V2O5 could facilitate the Li+ intercalation/deintercalation process of the nickel-rich cathode material and stabilize its layered structure after reacting with surface lithium residuals, and the rGO with excellent electronic conductivity is helpful to facilitate the transfer of electrons. Therefore, the V2O5/rGO hybrid coating layer not only prevents the surface against corrosion by electrolyte, but also improves the electronic and ionic conductivity of the material. The results showed that the cycling and rate performances of the designed material are more superior than those of the pristine material. The designed material performed an outstanding capacity of 145.7 mAh g−1 at 10 C, and the capacity retention was 90.43% at 1 C after 100 cycles, which is much higher than the pristine material. This work provides an effective strategy for improving the electrochemical performances of nickel-rich cathode materials.

Nickel-rich layered LiNi0.8Mn0.1Co0.1O2 with dual gradients on both primary and secondary particles in lithium-ion batteries

The Li + /Ni 2+ mixing in LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) leads to fast battery capacity decay. Here we report a dual-gradient nickel-rich layered cathode material (D-NMC811), using nickel-based metal organic framework of Ni-MOF-74. The formation of a protective layer with rock salt phase due to the reduced nickel oxidation state on the surface of the primary particles resists internal strain and suppresses further phase transition, thus alleviating crack generation. After 300 cycles at ⅓ C, a high half-cell capacity retention of 88.50% with 0.038% decay per cycle is observed. The full-cell battery displays a high capacity retention of >86.7% with a Coulombic efficiency of >99.86% at ⅓ C after 300 cycles. The 300 mAh pouch cell delivers an energy density of 216.4 Wh/kg. After 500 cycles at 1.0 C, it still displays 84.1% capacity retention while the battery with conventional NMC811 only shows a retention of 53.0% after 400 cycles. • Nickel-rich layered NMC material formed with MOF • Dual element concentration gradient on both primary and secondary particles • Enhanced structure stability through thin rock salt layer on surface • Improved battery capacity retention and cyclability Shang et al. report a nickel-rich cathode material with dual concentration gradients on both primary and secondary particles. The improved structure reliability of D-NMC811 during long cycling makes it promising for applications in high energy-density lithium ion batteries.

Mussel-inspired polydopamine-assisted uniform coating of Li+ conductive LiAlO2 on nickel-rich LiNi0.8Co0.1Mn0.1O2 for high-performance Li-ion batteries

A Li+ conductive LiAlO2 coating layer was uniformly covered on the surfaces of a nickel-rich LiNi0.8Co0.1Mn0.1O2 cathode material through a mussel-inspired, adhesive polydopamine-assisted approach. The adhesive and uniform PDA pre-coating on the Ni0.8Co0.1Mn0.1(OH)2 microspherical surfaces could act as a superior mediator to conformally concentrate the Al3+ precursor on the microsphere surfaces through chemical complexation, thus resulting in a uniform LiAlO2 coating on the LiNi0.8Co0.1Mn0.1O2 microspherical surfaces. The PDA-assisted uniform coating layer of Li+ conductive LiAlO2 could offer multifunctional effects, including effective prohibition of side-reactions between the LiNi0.8Co0.1Mn0.1O2 and electrolyte, significant suppression of the Li/Ni mixing in the LiNi0.8Co0.1Mn0.1O2 crystal lattices, and high Li-ion conductivity for fast electrochemical reactions. Therefore, the PDA-assisted LiAlO2 coated LiNi0.8Co0.1Mn0.1O2 cathode material ([email protected]) presents outstanding cycling stability and rate performance with high discharge capacity of 209 mAh/g at the 1st cycle at the current rate of 0.2 C, 178 mAh/g at the 100th cycle at the current rate of 0.2 C, 138 mAh/g at the 200th cycle at the current rate of 2 C, and 114 mAh/g at the 200th cycle at the current rate of 5 C. These encouraging results demonstrate that the mussel-inspired, adhesive PDA-assisted uniform coating of Li+ conductive LiAlO2 is a promising strategy to achieve high performance of nickel-rich layered oxide cathode material for advanced Li-ion secondary batteries.

Building a stabilized structure from surface to bulk of Ni-rich cathode for enhanced electrochemical performance

Nickel-rich layered oxides are considered to be one of the most promising candidates of cathode material for the next generation Li-ion batteries (LIBs) due to their high specific capacity. However, the capacity fading and poor rate capability caused by the interface instability and structure degradation hinder their commercial applications. Herein, we propose a one-step strategy to stabilize the nickel-rich cathode material through a synergistic effect of surface engineering and lattice doping. The interfacial structure stability is improved by a uniform nano-coating of Gd2O3&LiGdO2 with an ultra-high electronic conductivity, the lattice degradation and grain cracks have been suppressed by gradient Gd-doping. It exhibits a distinguish discharge capacity of 62.68 mAh g − 1 at a super high rate of 50 C within the voltage range of 2.7 - 4.5 V, as well as suppresses the capacity decay at high temperature.

Kinetics behavior of single-crystal nickel-rich cathode materials at different cut-off voltages

Kinetics behavior of single-crystal nickel-rich cathode materials at different cut-off voltages

Construction of Li3PO4 nanoshells for the improved electrochemical performance of a Ni-rich cathode material.

A Li3PO4 nanocoating around a nickel-rich cathode material was successfully constructed via controlling the reaction between the electrode material and a preformed phosphorus-containing polymeric nanoshell; this not only effectively tackles the alkali residue challenge, but it also contributes to much-improved electrochemical performance being shown by a high-energy cathode.

Improved High-Potential Property of Ni-Rich LiNi0.8Co0.1Mn0.1O2 with a Garnet Ceramic LLZTO Surface Modification in Li-Ion Batteries

The Ni-rich LiNixCoyMn1–x–yO2 with high specific capacity and superior thermal stability under a high cutoff voltage (>4.3 V) will play a critical role in high-power lithium-ion batteries (LIBs). In this paper, LiNi0.8Co0.1Mn0.1O2 (NCM811) equipped with a stable garnet ceramic Li6.5La3Zr1.5Ta0.5O12 (LLZTO) nanoshell is successfully synthesized via a simple wet chemical approach. X-ray diffraction, scanning electron microscope (SEM), energy-dispersive spectrometer (EDS) element mapping, and transmission electron microscopy (TEM) confirm the presence of LLZTO on the NCM811 surface. The NCM811 with 2 wt % LLZTO (2-NCM811) can deliver a superior specific capacity of 144.4 mAh·g–1 at 1C (2.8–4.3 V) after 100 cycles, accompanied by a capacity retention rate as high as 81.1%. But pristine NCM811 has a discharge capacity of only 119.6 mAh·g–1 and a capacity retention rate as low as 69.5% under the same condition. What is more, 2-NCM811 exhibits an enhanced discharge capacity of 129.6 mAh·g–1 at 1C (2.8–4.5 V) after 100 cycles and a high capacity retention rate of 62.9%, which are superior to those of pristine NCM811 (110.0 mAh·g–1, 57.6%). The improved high-potential performance of 2-NCM811 can be attributed to the positive role of the LLZTO shell, which enhances the structural stability and simultaneously inhibits adverse side reactions at the surface of 2-NCM811 during cycling. Based on the above advantages, LLZTO with three-dimensional (3D) diffusion pathways and high ion conductivity is expected to be the most prospective material for the surface modification engineering of nickel-rich cathode materials in lithium-ion batteries (LIBs).

Enhancement of electrochemical performance in lithium-ion battery via tantalum oxide coated nickel-rich cathode materials

Nickel-rich cathode materials are increasingly being applied in commercial lithium-ion batteries to realize higher specific capacity as well as improved energy density. However, low structural stability and rapid capacity decay at high voltage and temperature hinder their rapid large-scale application. Herein, a wet chemical method followed by a post-annealing process is utilized to realize the surface coating of tantalum oxide on LiNi0.88Mn0.03Co0.09O2, and the electrochemical performance is improved. The modified LiNi0.88Mn0.03Co0.09O2 displays an initial discharge capacity of ∼ 233 mAh/g at 0.1 C and 174 mAh/g at 1 C after 150 cycles in the voltage range of 3.0 V–4.4 V at 45 °C, and it also exhibits an enhanced rate capability with 118 mAh/g at 5 C. The excellent performance is due to the introduction of tantalum oxide as a stable and functional layer to protect the surface of LiNi0.88Mn0.03Co0.09O2, and the surface side reactions and cation mixing are suppressed at the same time without hampering the charge transfer kinetics.