Ni-rich Layered Cathode Materials Research Articles

Surface-Modified Quaternary Layered Ni-Rich Cathode Materials by Li2ZrO3 for Improved Electrochemical Performance for High-Power Li-Ion Batteries

Quaternary Ni-rich layered cathodes are one of the most intriguing yet challenging next-generation cathode materials, and their high Ni content has made it difficult to obtain long-term cyclability. In this paper, we report the improved electrochemical performance of high-power long-life Ni-rich layered cathode materials (LiNi0.90Co0.04Mn0.03Al0.03O2, denoted NCMA), synthesized in a Couette–Taylor reactor, after depositing a homogeneous surface coating of Li2ZrO3 (LZO). Morphological analyses revealed that the thickness of the LZO coating was approximately 2.5 nm and spread uniformly on the NCMA surface. X-ray photoelectron spectroscopy indicated that the content of Li residues on the surface had greatly decreased after coating with LZO. The electrochemical performance of the coated samples was greater than that of the bare NCMA; in particular, the 1 wt % LZO-coated cathode material had a capacity retention of 90.2% after 100 cycles at 1C (vs 74.6% for the bare NCMA). Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and the galvanostatic intermittent titration technique (GITT) indicated that the coating agent acted as a bridge that lowered the activation energy and polarization potential for a better Li+ ion transport. The polarization potential also decreased significantly after coating with LZO, leading to improved electrochemical kinetics. Postmortem studies after long cycling confirmed that the LZO coating layer enhanced the structural stability of the cathode.

Understanding high-temperature cycling-induced crack evolution and associated atomic-scale structure in a Ni-rich LiNi0.8Co0.1Mn0.1O2 layered cathode material

X-ray nano-computed tomography (nano-CT) and deep learning combined with Cs-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy were employed to investigate the atomic to microscopic structural evolution of LiNi0.8Co0.1Mn0.1O2 (NCM) upon cycling at 55 °C. Two types of intergranular cracks were clearly distinguished by nano-CT for cycled cathode particles; denoted open and closed cracks depending on whether or not the cracks reach the surface of the NCM secondary particles. The volume of high-temperature cycling-induced cracks quantified by deep learning increased drastically, particularly for the open cracks, and this phenomenon was accompanied by rapid degradation of capacity retention. Further precise STEM analysis of the crack regions revealed that migration of transition metal (TM) ions to the Li layer forms a rocksalt-like structure, and the associated reduction of TM ions, e.g., Ni3+ to Ni2+, predominately occurred in the open crack regions in the presence of penetrated electrolyte, even for regions extending to the center of the secondary particle. In contrast, in the closed crack regions, no significant atomic-scale structure distortion and limited reduction of TM ions was observed. Thus, our results provide fundamental guidance for improving the electrochemical performance of Ni-rich layered cathode materials for cycling at elevated temperatures.

Enhancing the Electrochemical Performance of Ni-Rich LiNi0.88Co0.09Al0.03O2 Cathodes through Tungsten-Doping for Lithium-Ion Batteries.

The tungsten-doped (0.5 and 1.0 mol%) LiNi0.88Co0.09Al0.03O2 (NCA) cathode materials are manufactured to systematically examine the stabilizing effect of W-doping. The 1.0 mol% W-doped LiNi0.88Co0.09Al0.03O2 (W1.0-NCA) cathodes deliver 173.5 mAh g−1 even after 100 cycles at 1 C, which is 95.2% of the initial capacity. While the capacity retention of NCA cathodes cycled in identical conditions is 86.3%. The optimal performances of the W1.0-NCA could be ascribed to the suppression of impendence increase and the decrease in anisotropic volume change, as well as preventing the collapse of structures during cycling. These findings demonstrate that the W-doping considerably enhances the electrochemical performance of NCA, which has potential applications in the development of Ni-rich layered cathode materials that can display high capacity with superior cycling stability.

Single-crystal structure helps enhance the thermal performance of Ni-rich layered cathode materials for lithium-ion batteries

Single-crystal (SC) LiNixCoyMn1−x−yO2 (NCM) materials have come into people’s field of view recently. The poor thermal stability of polycrystalline (PC) high-nickel NCM materials has always been an obvious shortcoming, and the thermal performance of SC materials is also an important factor which cannot be ignored. Therefore, it is necessary to investigate the safety difference between SC and PC NCM materials. In this research, LiNi0.8Co0.1Mn0.1O2 (NCM811) and LiNi0.6Co0.2Mn0.2O2 (NCM622) materials with single-crystal and polycrystalline structure are used to study the thermal performance, and the SC materials show obviously better thermal stability than PC materials. Due to the existence of internal crystal gaps, the PC materials have higher lithium-ion transport impedance and lower ion diffusion coefficient, which leads to more heat generation in the cycle process. At the same time, crystal gaps will increase the inhomogeneity of PC materials during charging and discharging, along with the rise of delithiation degree in some parts of the materials, making the structural damage more serious, which would reduce the binding of oxygen and become the initiating factor of oxygen release in advance. In conclusion, the single-crystal structure can improve the thermal properties of high nickel NCM materials during the cycle and under high temperature conditions.

The effect of high-temperature storage on the reaction heterogeneity of Ni-rich layered cathode materials

Ni-rich cathode materials with high energy and power densities have been used in Li-ion batteries for next-generation electric vehicles. However, Ni-rich cathode materials undergo severe structural degradation during operation in high-temperature environments, leading to critical performance degradation. Herein, we investigate the effect of high-temperature conditions on the crystal and electronic structure of Ni-rich cathode materials during the electrochemical reaction using synchrotron-based X-ray techniques. The bulk crystal structure of the Ni-rich layered material is maintained during high-temperature storage, but changes in the surface structure and particle integrity are observed. The conspicuous growth of an insulating NiO-like rock-salt phase on the particle surface results in an asymmetrical capacity loss in the form of charge fading, that is, capacity loss during charging. In addition to this surface degradation, particle fracture impedes the transport of Li-ions and electrons, producing several particle regions with reduced electrochemical activity. As a result, the reaction heterogeneity within the cathode is significantly intensified during the electrochemical reaction, aggravating the electrochemical performance. This study elucidates the origin of the performance degradation of Ni-rich cathode materials in high-temperature environments, which can offer valuable guidance for developing advanced Li-ion batteries with thermal durability.

Surface Stabilization of Ni-Rich Layered Cathode Materials via Surface Engineering with LiTaO3 for Lithium-Ion Batteries.

Recently, Ni-rich layered cathode materials have become the most common material used for lithium-ion batteries. From a structural viewpoint, it is crucial to stabilize the surface structures of such materials, as they are prone to undesirable side reactions and particle cracking in which intergranular microcracks form at the particle surfaces and then propagate inside. As a simplified engineering technique for obtaining Ni-rich cathode materials with high reversibility and long-term cycling stability, we propose a facile surface coating of piezoelectric LiTaO3 onto a Ni-rich cathode material to enhance the charge transfer reaction and surface structural integrity. Based on theoretical and experimental investigation, we demonstrate that this surface protection approach is effective at enhancing the reversibility and mechanical strength of Ni-rich cathode materials, leading to a stable cycle performance at up to 150 cycles, even at 60 °C. Furthermore, the piezoelectric characteristics of the surface LiTaO3 can enhance the rate capability of Ni-rich cathode materials at current densities of up to 2.0C. The results of this study provide a practical insight on the development of Ni-rich cathode materials for practical use in electric vehicle applications.

Preparation and electrochemical investigation of single-crystal LiNi0.6Co0.2Mn0.2O2 for high-performance lithium-ion batteries

Ni-rich layered cathode materials have large reversible capacity.

Maximizing the Energy Density and Stability of Ni-Rich Layered Cathode Materials with Multivalent Dopants Via Machine Learning

Maximizing the Energy Density and Stability of Ni-Rich Layered Cathode Materials with Multivalent Dopants Via Machine Learning

Microstructure and Surface Engineering Through Indium Modification on Ni-Rich Layered Cathode Materials for Enhanced Electrochemical Performance of Lithium-Ion Batteries

Microstructure and Surface Engineering Through Indium Modification on Ni-Rich Layered Cathode Materials for Enhanced Electrochemical Performance of Lithium-Ion Batteries

Enhancing the long-cycling performance of a LiNi0.8Co0.15Al0.05O2@LaNiO3 cathode material by surface modification

Herein, the introduction of hexagonal LaNiO3 on the surface of LiNi0.8Co0.15Al0.05O2 provides a protective and adaptable ultrathin layer to stabilize the microstructure of Ni-rich layered cathode materials, enhancing the electrochemical and thermal stability.

Transition metal-doped Ni-rich layered cathode materials for durable Li-ion batteries

Doping is a well-known strategy to enhance the electrochemical energy storage performance of layered cathode materials. Many studies on various dopants have been reported; however, a general relationship between the dopants and their effect on the stability of the positive electrode upon prolonged cell cycling has yet to be established. Here, we explore the impact of the oxidation states of various dopants (i.e., Mg2+, Al3+, Ti4+, Ta5+, and Mo6+) on the electrochemical, morphological, and structural properties of a Ni-rich cathode material (i.e., Li[Ni0.91Co0.09]O2). Galvanostatic cycling measurements in pouch-type Li-ion full cells show that cathodes featuring dopants with high oxidation states significantly outperform their undoped counterparts and the dopants with low oxidation states. In particular, Li-ion pouch cells with Ta5+- and Mo6+-doped Li[Ni0.91Co0.09]O2 cathodes retain about 81.5% of their initial specific capacity after 3000 cycles at 200 mA g−1. Furthermore, physicochemical measurements and analyses suggest substantial differences in the grain geometries and crystal lattice structures of the various cathode materials, which contribute to their widely different battery performances and correlate with the oxidation states of their dopants.

Regeneration of high-capacity Ni-rich layered cathode material from spent lithium-ion batteries

Ever-growing demand for electric vehicles promotes manufacture of lithium-ion batteries (LIBs) and accelerates consumption of some rare resources such as lithium and cobalt. In addition, numerous spent LIBs are sent to recycling depots every year. To explore a high-efficiency resource reuse, high-capacity Ni-rich LiNi0.92Co0.05Mn0.03O2 is synthesized from a Ni-Co-Cu-Fe alloy powder, a crude product from recycling spent LIBs. The alloy is firstly treated by an oxygen-assistant acid leaching, and then purified to remove Fe2+ and Cu2+. The purified leachate after being adjusted in chemical composition is directly made into Ni0.92Co0.05Mn0.03(OH)2 precursor via a co-precipitation method. X-ray diffraction and scanning electron microscope measurements indicate that the regenerated cathode material is well-crystallized and has spherical morphology with an average diameter of 3 µm. Energy dispersive spectroscopy shows that the Fe and Cu in the raw material are eliminated thoroughly. The electrochemical performance is evaluated as well. The cathode material delivers an initial discharge capacity of 231.8 mAh g−1 at 0.1 C. When tested at 0.5 C, it exhibits an initial discharge capacity of 213.4 mAh g−1, and a capacity retention of 57.6% after 400 cycles. At a high current density of 5 C, it still has a discharge capacity of 178.3 mAh g−1.

Outstanding enhancements in stability of LiNi0.8Mn0.1Co0.1O2 cathode by AlPO4/ACB double coating: Insights into surface structure and chemistry

Ni-rich layered cathode materials are highly attractive for high energy density lithiumion batteries, which however are facing serious surface issues. The effects of various coating materials on surface stability have been investigated, which mostly focus on exterior coating structure and properties. Herein, we focus on the surface variations of the cathode induced by the AlPO4/acetylene carbon black double coatings. It is the first time to discover that the AlPO4 coating greatly promotes crystallinity and lattice bonded oxygen near the surface of LiNi0.8Mn0.1Co0.1O2, which lead to decrease of Li/Ni disordering. The low ratio of Ni ions mixed in Li slab further prevents the serious Ni ions’ dissolution in electrolyte at high potential. Nevertheless, the discontinuous AlPO4 coating layer is unable to suppress the formation of Li2CO3 on surface. Additional carbon coating provides better coverage to effectively isolate the moisture and CO2 in air, and the content of surface Li2CO3 remarkably decreases. Eventually, the AlPO4/acetylene carbon black double coated LiNi0.8Mn0.1Co0.1O2 exhibits greatly enhanced charge/discharge stability at both 25℃ and 55℃.

Investigation on the structure and electrochemical performance of LiNi0.8Co0.1Mn0.1O2 modified with Sn

Ni-rich layered cathode materials are promising cathode materials for lithium-ion batteries with high energy density. To reveal the influence of Sn-coating and doping on the structure and electrochemical performances of Ni-rich layered cathode materials, LiNi0.8Co0.1Mn0.1O2, LiNi0.8Co0.1Mn0.1O2@xLi2SnO3 and LiNi0.8−xCo0.1Mn0.1SnxO2 (x = 0.02 and 0.04) are designed and synthesized. The effect of lithium-tin-oxide coating and Sn-doping on the structural and electrochemical behavior of Ni-rich cathode material are compared and investigated. Compared with the bare LiNi0.8Co0.1Mn0.1O2 cathode material, both LiNi0.8Co0.1Mn0.1O2@xLi2SnO3 and Sn-doped LiNi0.8−xCo0.1Mn0.1SnxO2 (x = 0.02 and 0.04) samples exhibit better electrochemical performances. The capacity retention for Li2SnO3-coated and Sn-doped materials after 270 cycles at 0.5C can reach as high as 93.7 and 96.6%, respectively. Besides, improved rate capabilities and thermal stability are also obtained for Li2SnO3-coated and Sn-doped materials. The superior electrochemical performances and enhanced thermal stability of Li2SnO3 coated samples are mainly ascribed to the higher interfacial stability and those of Sn-doped materials may be mainly due to higher structural stability and lower polarization than those of the bare LiNi0.8Co0.1Mn0.1O2 cathode material. These results indicate that the introduction of Sn ions, especially Sn doping, may be an effective strategy to improve the performance of Ni-rich layered cathode materials.

Understanding the formation of antiphase boundaries in layered oxide cathode materials and their evolution upon electrochemical cycling

Understanding the formation of antiphase boundaries in layered oxide cathode materials and their evolution upon electrochemical cycling

Impact of Dry Particle Fusion Coating of Tungsten Oxide on Ni-Based Positive Electrode Materials for Li-Ion Batteries

Ni-rich layered transition metal(TM) oxides LiNixTM1-xO2 (TM = Al, Mn, Mg, etc) are attractive for the positive electrode of Li-ion batteries because they have high specific and volumetric capacity 1–3 However, most Ni-rich layered transition metal oxides show poor capacity retention when cycled above 4.14 V vs Li/Li+, even though capacity retention when cycled below 4.14 V is excellent. Solving this mystery and improving capacity retention when Ni-rich layered transition metal oxides are required to deliver high specific capacity is of great importance.Tungsten doping has been reported to improve capacity retention of layered positive electrode materials when charged above 4.14 V. Ryu et al. found that the phase transitions were suppressed for tungsten doped layered oxide materials.4 Tungsten doping in Li[Ni0.9Co0.09W0.01]O2 (NCW) created secondary particles composed of thin directionally elongated needle-like primary particles. These particle morphology changes were claimed to be the reason for greatly improved capacity retention. The NCW cathode retained 92% of its initial capacity after 1000 cycles compared to only 63% for NCA.5 Microcrack formation by anisotropic volume expansion was found to be suppressed in secondary particles having these nanosized needle-like primary particles.5,6 Dry particle fusion of Al2O3 on Ni(OH)2 followed by lithiation has been shown to be an effective method to improve the capacity retention of positive electrode materials.7 In this work, tungsten-containing Ni-rich electrode materials containing 0.5, 1 and 2% W (compared to Ni) were made by dry particle fusion of WO3 on Ni(OH)2 followed by lithiation. The W-containing Ni-rich layered cathode materials had considerably improved capacity retention in agreement with previous reports. Figure 1a shows a W EDS map of some particles of Ni(OH)2 with 2 mol% WO3 after lithiation which shows that W ends up uniformly distributed inside the particles. Figure 1b shows that Ni(OH)2 coated with 0.5, 1 and 2 mol% WO3 followed by lithiation had better capacity retention than that of LiNiO2. Of all the samples prepared, Ni(OH)2 coated with 1 mol% WO3, followed by lithiation, had the largest specific discharge capacity and the best capacity retention. Figure 1c shows the specific discharge capacity vs. cycle number of Ni(OH)2 coated with 1 mol% WO3, followed by lithiation and Ni(OH)2 coated with 3 wt% Al2O3, followed by lithiation (corresponding to 5.17 mol% Al) reported in our previous work.7 The cycling performances of these two materials match almost exactly, indicating that they are equivalent materials. TEM and synchrotron based analysis are on-going to hopefully resolve the question: “Where is the W in these materials? – In a second phase or substitutional for Ni in the layered structure. Full coin cell cycling performance will be presented showing good capacity retention to 4.28 V vs Li/Li+. dVdQ analysis will also be presented allowing the cell degradation mechanism to be better understood.Reference U. H. Kim, D. W. Jun, K. J. Park, Q. Zhang, P. Kaghazchi, D. Aurbach, D. T. Major, G. Goobes, M. Dixit, N. Leifer, C. M. Wang, P. Yan, D. Ahn, K. H. Kim, C. S. Yoon, and Y. K. Sun, Energy Environ. Sci., 11, 1271–1279 (2018).S. T. Myung, F. Maglia, K. J. Park, C. S. Yoon, P. Lamp, S. J. Kim, and Y. K. Sun, ACS Energy Lett., 2, 196–223 (2017).H. Li, M. Cormier, N. Zhang, J. Inglis, J. Li, and J. R. Dahn, J. Electrochem. Soc., 166, A429–A439 (2019).H.-H. Ryu, G.-T. Park, C. S. Yoon, and Y.-K. Sun, J. Mater. Chem. A, 7, 18580–18588 (2019) http://xlink.rsc.org/?DOI=C9TA06402H.H. Ryu, K. Park, D. R. Yoon, A. Aishova, C. S. Yoon, and Y. Sun, Adv. Energy Mater., 9, 1902698 (2019) https://onlinelibrary.wiley.com/doi/abs/10.1002/aenm.201902698.H. H. Sun, H.-H. Ryu, U.-H. Kim, J. A. Weeks, A. Heller, Y.-K. Sun, and C. B. Mullins, ACS Energy Lett., 5, 1136–1146 (2020) https://pubs.acs.org/doi/10.1021/acsenergylett.0c00191.C. Geng, A. Liu, and J. R. Dahn, Chem. Mater., 32 (2020). Figure 1

Cover Feature: Sublimated Se‐Induced Formation of Dual‐Conductive Surface Layers for High‐Performance Ni‐Rich Layered Cathodes (ChemElectroChem 22/2021)

The Cover Feature shows a method to improve the electrochemical performance of Ni-rich layered cathode materials by inducing sublimation gaseous Se reaction to construct the dual-conductive coating. The sublimed gaseous Se reacts with residual Li compounds to form a Li2SeO4 coating on the surface of the secondary particles, which simultaneously promotes the transmission of Li ions and reduces electrode-electrolyte side reactions. Moreover, gaseous Se penetrates between the primary particles within the secondary particles to promote electron transmission. More information can be found in the Article by L. Chen, S. Chen et al.

Structure and Charge Regulation Strategy Enabling Superior Cyclability for Ni-Rich Layered Cathode Materials.

Ni-rich layered oxides are significantly promising cathode materials for commercial high-energy-density lithium-ion batteries. However, their major bottlenecks limiting their widespread applications are capacity fading and safety concerns caused by their inherently unstable crystal structure and highly reactive surface. Herein, surface structure and bulk charge regulation are concurrently achieved by introducing high-valence Ta5+ ions in Ni-rich cathodes, which exhibit superior electrochemical properties and thermal stability, especially a remarkable cyclic stability with a capacity retention of 80% for up to 768 cycles at a 1C rate versus Li/Li+ . Due to the partial Ta enrichment on surface, the regulated surface enables high reversibility of Li+ insertion/extraction by preventing surface Ni reduction in deep charging. Moreover, bulk charge regulation that boosts charge density and its localization on oxygen remarkably suppresses microcracks and oxygen loss, which in turn prevents the fragmentation of the regulated surface and structural degradation associated with oxygen skeleton. This study highlights the significance of an integrated optimization strategy for Ni-rich cathodes and, as a case study, provides a novel and deep insights into the underlying mechanisms of high-valence ions substitution of Ni-rich layered cathodes.

Slower capacity/voltage degradation of surface engineered LiNi0.92Co0.05Mn0.03O2 cathode for lithium-ion batteries

Ni-rich layered oxides are considered as a promising commercial cathode material due to high energy density and low cost. However, the severe capacity degradation and poor rate capability caused by structural collapse during long cycles limit their practical application. Herein, a NASICON-structured Li2AlZr(PO4)3 is constructed on the surface of LiNi0.92Co0.05Mn0.03O2 for stabilizing the layered structure. In addition, the construction process consumes the lithium residues on the surface of the material particles, thus reducing alkalinity of the material surface. Meanwhile, the electrochemical properties of the samples are studied. The capacity of the 1 wt% Li2AlZr(PO4)3 coated sample shows 144.2 mAh g−1 with a discharge middle voltage of 3.71 V after 400 cycles under the voltage range of 2.7–4.3 V. Further studies confirm that the uniform NASICON coating can effectively alleviate the structural degradation and intergranular cracks after long-term cycling. The research results illustrate the feasibility of the practical application of the modification strategy, which can be popularized in Ni-rich layered cathode materials.

Enhancing the structural stability and capacity retention of Ni-rich LiNi0.7Co0.3O2 cathode materials via Ti doping for rechargeable Li-ion batteries: Experimental and computational approaches

The Ni-rich cathodes are considered as the next generation candidate cathode material of lithium-ion batteries due to their high-energy–density and environmentally friendly. In this study, the Ni-rich, LiNi0.7Co0.3O2 cathodes material was doped by titanium (Ti) via a self-propagating combustion method. The role of Ti species and its effects on the structural and electrochemical performance of the cathode materials were investigated through experimental and first principles studies. From the XRD results, all materials possessed a single phase with a hexagonal layered structure of the R-3m space group. The Rietveld refinement revealed that the lattice of the Ti-doped LiNi0.7Co0.3O2 sample was found to be expanded in the c-axis and has a lower cation mixing as compared to the pristine samples, which can ease the movement of Li-ions during the delithiation/lithiation process. After 70th cycle, the discharge capacity of the Ti-doped LiNi0.7Co0.3O2 sample possess an excellent capacity retention of 91.9% with a specific discharge capacity of 132.3 mAhg−1 as compared to the pristine sample with only has 86.2 mAhg−1. This can be explained by first-principles study where it was found that the Li-O distances for LNCT become expand after the delithiation process which ease the Li-ions diffusion during cycling. As a whole, the addition of Ti species into the Ni-rich layered cathode materials was found to stabilise the crystal structure of LiNi0.7Co0.3O2 and subsequently improved the lithium-ion kinetics of the layered cathode materials. Apart from lithium nickel manganese cobalt oxide (NMC) and lithium nickel cobalt aluminium oxide (NCA), this study demonstrated that LiNi0.6Co0.3Ti0.1O2 can also serve as potential cathode material for rechargeable Li-ion batteries.