Nickel-rich Layered Oxide Research Articles

Constructing an organic artificial cathode electrolyte interphase of multi-functions on single-crystal LiNi0.8Co0.1Mn0.1O2 cathode

Nickel-rich layered oxide materials are of great significance for high energy density lithium-ion batteries due to their high theoretical capacity. However, interfacial side reaction is known to be an important cause for their electrochemical degradation. Herein, we construct an organic artificial solid electrolyte interface with 4-cyanophenylboronic acid (4-CPBA) as a precursor on a single-crystal LiNi0.8Co0.1Mn0.1O2 (NCM811) surface. As a strong electron-absorbing group, cyano groups help to anchor the interfacial Ni2+ while the boronic acid groups contributes to remove the residual lithium and passivate the NCM811 surface. After wrapping the 11 nm thick artificial cathode electrolyte interface (CEI) precursor, the prepared NCM811 cathode exhibits an improved first coulomb efficiency of 93.5% at high temperature. A capacity retention of 82.5% after 200 cycles is obtained at 1C charge-discharge condition, significantly higher than that of 61.0% for the pristine cathode. The post analysis reveals that 4-CPBA is involved in the formation of CEI film and of many different functions on the cathode surface. The new interfacial modification strategy based on the synergistic interaction between the high nickel cathode material and functional organic molecules expands CEI technologies on nickel rich cathode materials.

Operando visualization of kinetically induced lithium heterogeneities in single-particle layered Ni-rich cathodes

<h2>Summary</h2> Understanding how lithium-ion dynamics affect the (de)lithiation mechanisms of state-of-the-art nickel-rich layered oxide cathodes is crucial to improve electrochemical performance. Here, we directly observe two distinct kinetically induced lithium heterogeneities within single-crystal LiNi_xMn_yCo_(1−x−y)O₂ (NMC) particles using recently developed <i>operando</i> optical microscopy, challenging the notion that uniform (de)lithiation occurs within individual particles. Upon delithiation, a rapid increase in lithium diffusivity at the beginning of charge results in particles with lithium-poor peripheries and lithium-rich cores. The slow ion diffusion at near-full lithiation states—and slow charge transfer kinetics—also leads to heterogeneity at the end of discharge, with a lithium-rich surface preventing complete lithiation. Finite-element modeling confirms that concentration-dependent diffusivity is necessary to reproduce these phenomena. Our results demonstrate how kinetic limitations cause significant first-cycle capacity losses in Ni-rich cathodes.

Fast charging of energy-dense lithium-ion batteries.

Lithium-ion batteries with nickel-rich layered oxide cathodes and graphite anodes have reached specific energies of 250-300 Wh kg-1 (refs. 1,2), and it is now possible to build a 90 kWh electric vehicle (EV) pack with a 300-mile cruise range. Unfortunately, using such massive batteries to alleviate range anxiety is ineffective for mainstream EV adoption owing to the limited raw resource supply and prohibitively high cost. Ten-minute fast charging enables downsizing of EV batteries for both affordability and sustainability, without causing range anxiety. However, fast charging of energy-dense batteries (more than 250 Wh kg-1 or higher than 4 mAh cm-2) remains a great challenge3,4. Here we combine a material-agnostic approach based on asymmetric temperature modulation with a thermally stable dual-salt electrolyte to achieve charging of a 265 Wh kg-1 battery to 75%(or70%) state of charge in 12(or11) minutes for more than 900(or2,000) cycles. This is equivalent to a half million mile range in which every charge is a fast charge. Further, we build a digital twin of such a battery pack to assess its cooling and safety and demonstrate that thermally modulated 4C charging only requires air convection. This offers a compact and intrinsically safe route to cell-to-pack development. The rapid thermal modulation method to yield highly active electrochemical interfaces only during fast charging has important potential to realize both stability and fast charging of next-generation materials, including anodes like silicon and lithium metal.

Enable High-Energy LiNi0.5Co0.2Mn0.3O2 by Ultra-Thin Coating through Wet Impregnation

A high cut-off voltage is required for nickel-rich layered oxide LiNixCoyMnzO2 (NCM) to meet the high energy density requirement of lithium-ion batteries in electric vehicles. However, such a high voltage application leads to an unstable interface between NCM and liquid electrolytes. To stabilize the interface, the facile wet impregnation method has been developed to apply an ultra-thin Al2O3 coating layer on the NCM particles. This coating layer was found to have a strong interaction with the NCM and resulted in Al-doped NCM at the surface structure of NCM. The change of surface structure can not only reduce the surface resistance of lithium diffusion of LiNi0.5Co0.2Mn0.3O2 (NCM523), but also stabilize the solid electrolyte interface between NCM523 and the electrolyte with the cut-off voltage of 4.5 V vs. Li/Li+. Compared to other coating methods, wet impregnation coating can provide an ultra-thin and uniform coating with surface doping on NCM particles. Furthermore, this scalable coating method can be applied to various electrode materials without adding much additional cost.

Correlating Morphological and Structural Evolution with the Electrochemical Performance of Nickel-Rich Cathode Materials: From Polycrystal to Single Crystal

Nickel-rich layered oxides (Ni ≥ 90%) have been recognized as a promising cathode material for Lithium-ion batteries (LIBs) owing to their high energy density and low cost. Herein, we prepared 20 LiNi0.90Co0.06Mn0.04O2 (Ni90) samples with various morphologies by regulating sintering temperature and the lithium to transition metal ratio. The correlation between the synthesis conditions, structural properties, and electrochemical performance of Ni90 materials was thoroughly investigated during the evolution from polycrystal to single crystal. A positive and linear relationship was found between sintering temperature and primary particle size (PPS), which affect the electrochemical performance profoundly. Polycrystals with small PPS show a high discharge capacity and low polarization, while single crystals with large PPS have low discharge capacity but excellent cycling stability. Moreover, the sluggish kinetic properties of Ni90 materials at the end of discharge (a sharp drop in lithium-ion diffusion coefficient at the end of discharge) lead the morphology factors to a critical feature that dominates the total discharge capacity. Taking discharge capacity and cycling stability into integrated consideration, the quasi-single crystal Ni90 materials with moderate PPS and the lowest cation disordering is the first choice. These findings contribute to a better understanding of polycrystalline and single-crystal Nickel-rich cathode materials for LIBs.

A Mini Review on Ni-rich Layered Oxide Cathode Materials

The global energy demand and increasing global warming are threats to the planet; therefore, replacing internal combustion engine vehicles to electric vehicles is prerequisite. Rechargeable batteries are key component to operate electric vehicles, among which lithium-ion batteries are governing the industry. After the successful discovery of Goodenough’s LiCoO2, layered oxides are emerging and are considered to be the next-generation cathodes. Ni-rich layered oxides are the new-generation cathode material owing to high specific capacity, high energy density, high operating voltage and low cost. Substitution of Co, Mn and Al is advantageous to compensate for the loss of the storage capacity and structural degradation. This review aims to discuss the characteristics, structure and preparation methods for nickel-rich layered oxide cathode material.

Chemical and structural evolution during solid-state synthesis of cobalt-free nickel-rich layered oxide cathode

In contrast to the surging need for the cobalt-free nickel-rich layered transition metal oxide cathodes in lithium-ion batteries, the chemical and structural change in the solid-state synthesis of such materials is still not clear enough. Herein, the solid-state synthetic process of LiNi0.94Mn0.04Al0.02O2 from room temperature to excessive temperature is systematically studied to present a detailed and full view of the structure transformation, valence variation, and impurity phase generation alongside the synthetic process. The results indicate three stages of the synthetic process, that is the decomposition-chemical combination stage below 500 °C, the regularization of R3¯m phase stage at 500∼800 °C, and the excessive calcining stage above 800 °C. Surprisingly, during the first stage below 500 °C, the precursor and alkali lithium start to react at a much lower temperature (e.g., 300 °C) than expected, accompanied by the integration of a considerable amount of Li element into the bulk of precursor and the oxidization of Ni. Specifically, the stoichiometric ratio of Li/TM in LixTMO2 is 37%, 55%, and ∼100% at 300, 400, and 500 °C, together with more than half of Ni oxidized to +3. However, on the third stage above 800 °C, R3¯m phase in LixTMO2 will become unstable and lead to the emergence of NiO-like rock-salt, accompanied by the reduction of a portion of Ni3+ and significant Li loss. The stoichiometric ratio of Li/TM in LixTMO2 is 79% at 1000 °C. These findings provide an insight into the solid-state synthesis of cobalt-free nickel-rich layered transition metal oxide cathodes.

Building Practical High-Voltage Cathode Materials for Lithium-Ion Batteries.

It has long been a global imperative to develop high-energy-density lithium-ion batteries (LIBs) to meet the ever-growing electric vehicle market. One of the most effective strategies for boosting the energy density of LIBs is to increase the output voltage, which largely depends upon the cathode materials. As the most-promising cathodes for high-voltage LIBs (>4V vs Li/Li+ ), four major categories of cathodes including lithium-rich layered oxides, nickel-rich layered oxides, spinel oxides, and high-voltage polyanionic compounds still encounter severe challenges to realize the improvement of output voltage while maintaining high capacity, fast rate capability, and long service life. This review focuses on the key links in the development of high-voltage cathode materials from the lab to industrialization. First, the failure mechanisms of the four kinds of materials are clarified, and the optimization strategies, particularly solutions that are easy for large-scale production, are considered. Then, to bridge the gap between lab and industry, the cost management, safety assessment, practical battery-performance evaluation, and sustainability of the battery technologies, are discussed. Finally, tough challenges and promising strategies for the commercialization of high-voltage cathode materials are summarized to promote the large-scale application of LIBs with high energy densities.

Monitoring the Electrochemical Capacitance By in Situ Impedance Spectroscopy As Indicator for Particle Cracking of (Nickel-Rich) Cathode Active Materials: Development of a Simplified Measurement Setup

Due to their high specific capacity, the market share of nickel-rich layered lithium nickel cobalt manganese oxides (NCMs, LiNixCoyMnzO2, x+y+z = 1) as cathode active materials (CAMs) for lithium-ion batteries is constantly growing. With higher nickel content, however, the increased capacity is often accompanied by shorter cycle life due to undesired side reactions on the CAM/electrolyte interface. As the optimization of the electrochemical performance of lithium-ion batteries by the adjustment of the composition of the cathode active materials has come to a limit, the focus has shifted to the modification of the morphological aspects. One way to minimize side reactions is to reduce the specific surface area of the CAM through a greater NCM crystallite size or through a customized particle morphology, both exhibiting less particle cracking upon charge/discharge cycling [1]. However, new methodologies for the quantification of aspects such as particle size, particle cracking, and surface area change are needed.Recently, we have developed a novel in situ analytical method which is able to quantify the increase of the CAM surface area upon extended charge/discharge cycling using electrochemical impedance spectroscopy (EIS) [2]. There, we make use of the direct correlation between the capacitance and the surface area of the electrode, whereby an increase of the capacitance indicates cracking of CAM particles, caused by the repeated volume change of the NCM material upon (de)lithiation and/or oxygen release at high state of charge [3]. In these works, the direct relationship between capacitance and NCM particle surface area was validated by ex situ krypton physisorption measurements.Unfortunately, this impedance-based method relies on a sophisticated experimental setup, using a micro-reference electrode (i.e., a gold-wire µ-RE) and a partially pre-lithiated lithium titanate (LTO) counter electrode. Therefore, in this study, we deduce a stepwise simplification of the capacitance measurements from the setup with a µ-RE and a pre-lithiated LTO counter electrode to a conventional coin half-cell setup, which is commonly used in industry for quick and routine material benchmarking. Additionally, it will be shown that the capacitance does not have to be extracted from a full impedance spectrum provided by an impedance analyzer, but that it can be obtained solely from a low-frequency single-point impedance measurement performed at a battery cycler. The working principle of this approach is validated using four different cell and potentiostat / battery cycler configurations over several charge/discharge cycles [4].The here demonstrated setup provides a simple method suitable for conventional coin half-cells to identify surface area changes of cathode active materials, being easily implemented in standard cycling procedures. Reference s [1] W. Li, E. M. Erickson, and A. Manthiram, Nature Energy 5 26 (2020).[2] S. Oswald, D. Pritzl, M. Wetjen, and H. A. Gasteiger, J. Electrochem. Soc. 167 100511 (2020).[3] S. Oswald, D. Pritzl, M. Wetjen, and H. A. Gasteiger, J . Electrochem . Soc . 168 120501 (2021).[4] S. Oswald, F. Riewald, H. A. Gasteiger, manuscript in preparation. Acknowledgements This work is financially supported by the BASF SE Network on Electrochemistry and Battery Research.

The Role of Gas Evolution in Particle Surface Cracking in Nickel-Rich Lithium-Ion Cathode Materials

Nickel-rich layered oxide cathode materials (LiNixTM(1-x)O2 where x > 0.8) are of great interest because they offer increased capacity compared to current commercial materials while maintaining compatibility with supply chain and production processes already in place. However, recent studies have shown that these materials in their current form are unsuitable for commercial applications due to the accelerated degradation caused by replacing more stable transition metals with the relatively unstable nickel. While various strategies have already been proposed to mitigate this issue, the fundamental degradation mechanism still needs to be better understood to inform the design of the next generation of nickel-rich cathode materials. In this work, differential electrochemical mass spectrometry (DEMS) is combined with titration mass spectrometry (TiMS) to measure gases evolved in a lithium half-cell during cycling as well as surface species which evolve gas upon addition of strong acid to an extracted cathode. Along with qualitative observations of particle cracking by scanning electron microscopy (SEM), these results reveal correlations between particle cracking, electrolyte reactivity, and carbonate oxidation and deposition on the changing cathode surface in nickel-rich cathode materials.

(Invited, Digital Presentation) Pushing the Limits of High Nickel NMC Cathodes

Lithium-ion batteries now dominate electrochemical energy storage for vehicle propulsion and grid storage in addition to portable electronics. In 2022, they celebrate their 50th anniversary, and yet still achieve only 25% of their theoretical energy density. The dominant anode and cathode today are graphitic carbon and the layered NMC oxides, LI[NiMnCoAl]O2. Both need improving. Most of the carbon in the anode must go, and the NMCs need pushing to their limit and at the same time eliminating cobalt. I will today discuss the challenges faced as we push the limits of the NMCs to their limits, > 80% lithium cycling, and Ni>0.8 and Co <<0.1. The higher the Ni content the lower the charging voltage needed for a given cycling capacity, but the greater its surface and bulk reactivity. The issues discussed will include 1stcycle loss [1], high rate capability [2], cathode stability [3], and surface/bulk reactivity and the impact of surface/bulk modification [4,5] and the micron-size single crystals vs meatballs on these [6]. This work is being supported by DOE-EERE-BMR-Battery500 consortium.[1]. Hui Zhou, Fengxia Xin, Ben Pei, M. Stanley Whittingham, “What Limits the Capacity of Layered Oxide Cathodes in Lithium Batteries?”, ACS Energy Lett. 2019, 4: 1902−1906.[2]. Chunmei Ban, Zheng Li, Zhuangchun Wu, Melanie J. Kirkham, Le Chen, Yoon Seok Jung, E. Andrew Payzant, Yanfa Yan, M. Stanley Whittingham, and Anne C. Dillon “Extremely Durable High-Rate Capability of a LiNi0.4Mn0.4Co0.2O2 Cathode Enabled by Single–Wall Carbon Nanotubes”, Advanced Energy Materials, 2011, 1: 58-62.[3]. Hyung-Joo Noh, Sungjune Youn, Chong Seung Yoon, Yang-Kook Sun “Comparison of the structural and electrochemical properties of layered Li[NixCoyMnz]O2 (x = ¼ 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) cathode material for lithium-ion batteries”, J. Power Sources, 2013, 233: 121-130.[4]. Fengxia Xin, Hui Zhou, Yanxu Zong, Mateusz Zuba, Yan Chen, Natasha A. Chernova, Jianming Bai, Ben Pei, Anshika Goel, Jatinkumar Rana, Feng Wang, Ke An, Louis F. J. Piper, Guangwen Zhou, and M. Stanley Whittingham, “What is the Role of Nb in Nickel-Rich Layered Oxide Cathodes for Lithium-Ion Batteries?”, ACS Energy Letters, 2021, 6: 1377-1382.[5]. Ben Pei, Hui Zhou, Anshika Goel, Mateusz Zuba, Hao Liu, Fengxia Xin, and M. Stanley Whittingham, “Al Substitution for Mn during Co-Precipitation Boosts the Electrochemical Performance of LiNi0.8Mn0.1Co0.1O2”, J. Electrochemical Society, 2021, 68: 050532.[6]. Yujing Bi, Jinhui Tao, Yuqin Wu, Linze Li, Yaobin Xu, Enyuan Hu, Bingbin Wu, Jiangtao Hu, Chongmin Wang, JiGuang Zhang, Yue Qi and Jie Xiao, “Reversible planar gliding and microcracking in a single-crystalline Ni-rich cathode”, Science, 2020, 370: 1313-1317.

Operando Photonic Stopband Monitoring of Lithium-Ion Battery Electrodes

Research in lithium-ion batteries is often focused on optimising the electrode performance of either the anode1 or cathode2. One common research strategy is to explore alternative electrode material candidates for use as both the anode3 and cathode4. Another approach involves optimising the performance of existing electrode materials through structured electrode architectures with nano-sized features. Incorporating nanostructure into electrode design has reported advantages of shorter ion diffusion lengths and improved rate capability during cycling5. A common and simple technique for introducing nanostructure to electrodes is the use of a photonic crystal template, particularly inverse opal photonic crystals. The porous geometry, highly interconnected material and nano-sized features of the pore walls are all believed to contribute to improved electrochemical performance in inverse opal electrodes6 7.Photonic crystal materials are more than just a structural template and are renowned for their ability to tune the wavelengths of light propagating in the structure8 9. The repeating dielectric material comprising the structure reflects specific wavelengths, known as the photonic bandgap or stopband, depending on the size of the repeating lattice and the refractive index contrast between the composite materials. Tuning the photonic stopband of various inverse opal materials has been extensively studied10 11. Inverse opal battery electrodes have yet to exploit the optical potential of the photonic stopband.Here, we showcase a fundamentally new operando analysis technique for lithium-ion battery electrodes adopting a photonic crystal structure. Visible spectroscopy is used to monitor the presence and position of the photonic stopband of the electrode material during battery cycling, see Figure 1. Capitalizing on the sensitivity of the photonic stopband to lattice size and refractive index contrast, shifts or changes in the optical spectrum can be correlated to the electrode environment and material performance. Several optical effects are observed throughout the cycling process and linked back to the battery performance of the anode. A TiO2 inverse opal anode is reported on here, yet the technique is versatile and should be applicable to a wide range of electrode materials possessing a photonic crystal structure. References Kim, H.; Choi, W.; Yoon, J.; Um, J. H.; Lee, W.; Kim, J.; Cabana, J.; Yoon, W.-S., Exploring Anomalous Charge Storage in Anode Materials for Next-Generation Li Rechargeable Batteries. Chemical Reviews 2020, 120 (14), 6934-6976.Xu, J.; Dou, S.; Liu, H.; Dai, L., Cathode materials for next generation lithium ion batteries. Nano Energy 2013, 2 (4), 439-442.Liang, B.; Liu, Y.; Xu, Y., Silicon-based materials as high capacity anodes for next generation lithium ion batteries. Journal of Power Sources 2014, 267, 469-490.Manthiram, A.; Song, B.; Li, W., A perspective on nickel-rich layered oxide cathodes for lithium-ion batteries. Energy Storage Materials 2017, 6, 125-139.Mahmood, N.; Tang, T.; Hou, Y., Nanostructured Anode Materials for Lithium Ion Batteries: Progress, Challenge and Perspective. Advanced Energy Materials 2016, 6 (17), 1600374.McNulty, D.; Carroll, E.; O'Dwyer, C., Rutile TiO2 Inverse Opal Anodes for Li-Ion Batteries with Long Cycle Life, High-Rate Capability, and High Structural Stability. Advanced Energy Materials 2017, 7 (12), 1602291.McNulty, D.; Geaney, H.; Buckley, D.; O'Dwyer, C., High capacity binder-free nanocrystalline GeO2 inverse opal anodes for Li-ion batteries with long cycle life and stable cell voltage. Nano Energy 2018, 43, 11-21.John, S., Strong localization of photons in certain disordered dielectric superlattices. Phys. Rev. Lett. 1987, 58 (23), 2486-2489.Yablonovitch, E., Inhibited spontaneous emission in solid-state physics and electronics. Phys. Rev. Lett. 1987, 58 (20), 2059-2062.Schroden, R. C.; Al-Daous, M.; Blanford, C. F.; Stein, A., Optical Properties of Inverse Opal Photonic Crystals. Chemistry of Materials 2002, 14 (8), 3305-3315.Lonergan, A.; Hu, C.; O’Dwyer, C., Filling in the gaps: The nature of light transmission through solvent-filled inverse opal photonic crystals. Physical Review Materials 2020, 4 (6), 065201. Figure 1 (a) Schematic diagram of simultaneous electrochemical and optical characterisation techniques for photonic crystal electrodes. (b) Galvanostatic charge/discharge data for a TiO2 inverse opal electrode. (c) Optical spectrum for a TiO2 inverse opal submerged in LiPF6 electrolyte. (d) SEM image showing the ordered structure of a pristine TiO2 inverse opal. (e) Operando optical spectra obtained at 0.5 V intervals during discharge of the TiO2 inverse opal electrode. Figure 1

The Effect of Annealing on the Structure, Composition and Electrochemistry of NMC811 Coated with Al2O3 Using an Alkoxide Precursor

Increasing capacities and lowering costs of the cathode material is a key challenge in lithium ion-battery research. Towards this end, nickel-rich layered oxides of the formula Li[NixMnyCoy]O2 (NMC) with x ≥ 0.8 were developed. Compared to previously used cathodes such as LiCoO2 , nickel-rich NMCs reach lower costs by replacing most of the cobalt with nickel and they enable higher discharge capacities.1 Despite the presence of small amounts of cobalt and manganese as dopants to improve stability and rate-capability, these materials still show fast capacity fade during electrochemical cycling which cannot be overcome by modifying the ratio of their elements.2 New strategies to mitigate this degradation are therefore urgently needed for the use of these materials in practical applications such as electric vehicles.3 Most of the degradation that occurs in nickel-rich NMCs upon cycling starts at the cathode-electrolyte interface via surface reactions,oxygen evolution followed by rock-salt formationand transition metal dissolution.4–6 One way to slow down or stop these processes is by changing the nature of this interface through coatings. Although there is a large number of studies showing the benefits of using them, knowledge on the design of coatings with specific properties is still lacking.7,8 In this work, we develop a new solution-based deposition method for the synthesis of aluminium oxide coatings onto LiNi0.8Mn0.1Co0.1O2 (NMC811) secondary particles (Figure 1) and study the effect of annealing on their structure and electrochemical lifetime as new-generation cathode for lithium-ion batteries. Using energy dispersive X-ray spectroscopy (EDS) and X-ray fluorescence spectroscopy (XRF) we quantify the amount and distribution of aluminium oxide on the cathode particles. By using solid-state nuclear magnetic resonance (SS-NMR) and X-ray photoelectron spectroscopy (XPS), we track changes in the coating phase and composition as a function of annealing temperature. 27Al NMR spectroscopy provides direct evidence of the diffusion of the coating into the bulk of the particles leading to surface-layer doping. Finally, we evaluate the electrochemical performance of the coated materials in half cells using long-term galvanostatic cycling. This work provides insight on the effects of surface coating and doping on battery degradation and shows how, by carefully selecting synthetic conditions, coatings of cathode particles with tailored properties can be prepared.(1) Myung, S.-T.; Maglia, F.; Park, K.-J.; Yoon, C. S.; Lamp, P.; Kim, S.-J.; Sun, Y.-K. Nickel-Rich Layered Cathode Materials for Automotive Lithium-Ion Batteries: Achievements and Perspectives. ACS Energy Letters 2017, 2 (1), 196–223. https://doi.org/10.1021/acsenergylett.6b00594.(2) Noh, H.-J.; Youn, S.; Yoon, C. S.; Sun, Y.-K. Comparison of the Structural and Electrochemical Properties of Layered Li[NixCoyMnz]O2 (x = 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) Cathode Material for Lithium-Ion Batteries. Journal of Power Sources 2013, 233, 121–130. https://doi.org/10.1016/j.jpowsour.2013.01.063.(3) Kim, J.; Lee, H.; Cha, H.; Yoon, M.; Park, M.; Cho, J. Prospect and Reality of Ni-Rich Cathode for Commercialization. Advanced Energy Materials 2018, 8 (6), 1702028. https://doi.org/10.1002/aenm.201702028.(4) Rinkel, B. L. D.; Hall, D. S.; Temprano, I.; Grey, C. P. Electrolyte Oxidation Pathways in Lithium-Ion Batteries. J. Am. Chem. Soc. 2020, 142 (35), 15058–15074. https://doi.org/10.1021/jacs.0c06363.(5) Wandt, J.; Freiberg, A.; Thomas, R.; Gorlin, Y.; Siebel, A.; Jung, R.; Gasteiger, H. A.; Tromp, M. Transition Metal Dissolution and Deposition in Li-Ion Batteries Investigated by Operando X-Ray Absorption Spectroscopy. J. Mater. Chem. A 2016, 4 (47), 18300–18305. https://doi.org/10.1039/C6TA08865A.(6) Xu, C.; Märker, K.; Lee, J.; Mahadevegowda, A.; Reeves, P. J.; Day, S. J.; Groh, M. F.; Emge, S. P.; Ducati, C.; Layla Mehdi, B.; Tang, C. C.; Grey, C. P. Bulk Fatigue Induced by Surface Reconstruction in Layered Ni-Rich Cathodes for Li-Ion Batteries. Nat. Mater. 2020. https://doi.org/10.1038/s41563-020-0767-8.(7) Shi, Y.; Zhang, M.; Qian, D.; Meng, Y. S. Ultrathin Al2O3 Coatings for Improved Cycling Performance and Thermal Stability of LiNi0.5Co0.2Mn0.3O2 Cathode Material. Electrochimica Acta 2016, 203, 154–161. https://doi.org/10.1016/j.electacta.2016.03.185.(8) Neudeck, S.; Strauss, F.; Garcia, G.; Wolf, H.; Janek, J.; Hartmann, P.; Brezesinski, T. Room Temperature, Liquid-Phase Al2O3 Surface Coating Approach for Ni-Rich Layered Oxide Cathode Material. Chemical Communications 2019, 55 (15), 2174–2177. https://doi.org/10.1039/C8CC09618J. Figure 1

Nano Tomography of High Voltage Induced First Cycle Cracking in NMC811

Lithium nickel-manganese-cobalt (NMC) oxide-based Li-ion batteries have emerged as the most promising successor to LiCoO2 chemistry and could potentially facilitate ubiquitous adoption of Li-ion in mobile and transport systems. High specific capacities, high-rate capability, and long-term cycling abilities are driving much research into these cathode materials, forcing a greater nickel content with each iteration. NMC811’s high specific capacity makes it highly attractive for battery suppliers and users; however, it suffers significant capacity fade via several degradation modes, one being crack formation within secondary particles. The fresh surface exposed by cracking has been linked with parasitic reactions that evolve oxygen and potentially initiate the formation of inactive crystal structures. [1]X-ray computed tomography (CT) has been utilised extensively to image the morphology of battery particles and with the advancement of lab-based tomography systems, resolution on the nano scale is readily available.[2] Whilst in-situ studies are becoming the standard experimental operation for appraising the dynamic nature of these materials, in-situ cells are complicated for use in lab-based instruments due to their low flux, low energy and reduced working space. Thus, nano tomography rarely provides information that deconvolutes chemo-mechanical cracking from manufacturing defects and calendaring. However, in this work we have developed a unique technique to follow the progression of cracking at the nanometre scale by sequential correlated imaging of a micro-sized tab cut from the electrode.[3,4] This method allows for images of the pristine material to be acquired ex-situ before electrochemical testing, and then sequential imaging of the same region of interest in subsequent scans. Here, nano-CT imaging of the same region of the electrode while fully-lithiated and charged to 4.5 V unveils the propagation of cracks as a function of voltage, and their relaxation phenomena upon discharge.[1] Li, Tianyu, Xiao-Zi Yuan, Lei Zhang, Datong Song, Kaiyuan Shi, and Christina Bock. "Degradation mechanisms and mitigation strategies of nickel-rich NMC-based lithium-ion batteries." Electrochemical Energy Reviews 3, no. 1 (2020): 43-80.[2] Heenan, Thomas MM, Chun Tan, Jennifer Hack, Dan JL Brett, and Paul R. Shearing. "Developments in X-ray tomography characterization for electrochemical devices." Materials Today 31 (2019): 69-85[3] Tan, C., S. Daemi, T. Heenan, F. Iacoviello, A. S. Leach, L. Rasha, R. Jervis, D. J. L. Brett, and P. R. Shearing. "Rapid preparation of geometrically optimal battery electrode samples for nano scale X-ray characterisation." Journal of The Electrochemical Society 167, no. 6 (2020): 060512.[4] Tan, Chun, Andrew S. Leach, Thomas MM Heenan, Huw Parks, Rhodri Jervis, Johanna Nelson Weker, Daniel JL Brett, and Paul R. Shearing. "Nanoscale state-of-charge heterogeneities within polycrystalline nickel-rich layered oxide cathode materials." Cell Reports Physical Science (2021): 100647. Figure 1

Challenges and prospects of nickel-rich layered oxide cathode material

The increasing electromobility demands rechargeable batteries with high energy density and enhanced electrochemical properties. However, the commercialized lithium-ion batteries experience several critical challenges related to cost-effectiveness, long-term safety and calendar life. Ni-rich layered oxides, LiNixCoyMnzO2 (NCM) and LiNixCoyAlzO2 (NCA) (x + y + z = 1, x ≥ 0.8) have been considered as next-generation cathode materials with the capability to achieve high energy density (800 Wh kg−1) and high operating voltage with low cost. However, their intrinsic unstable behavior, including surficial/interfacial issues, fatigue, inter/intragranular cracking, parasitic side reactions and thermal runway, causes severe capacity and voltage fading, deprived rate capability, and safety concerns during the charge/discharge process. This review article focuses on degradation mechanisms, challenges, and the most recent approaches, including doping, surface coating, structural engineering, dual modification, concentration gradient, and single-crystal cathodes were precisely summarized. Besides, the new series of Ni-based cathodes were discussed to alter the primary microstructural particle by replacing Co/Mn/Al in NCM and NCA. Notably, the compatibility and interfacial challenges of Ni-rich cathodes with solid-state electrolytes were elaborated to stabilize the electrochemical performance of this high-voltage cathode in all-solid-state batteries (ASSBs). The outlook presents a perception towards the practical application of Ni-rich layered oxide cathode materials in electromobility.

Reinforcement of binder adhesion for nickel-rich layered oxide in lithium-ion batteries using perfluorinated molecular surface modification

Ni-rich layered oxides are considered the most promising candidates for cathode materials for use in electric vehicles because of their high energy density and low cost. However, the cyclability of Ni-rich layered oxide needs to be improved because it suffers from contact loss by microcracks owing to the large anisotropic volume changes during cycling. Furthermore, its unstable surface, which releases lithium impurities by water contamination, must also be mitigated. To improve the adhesive force with a polyvinyl fluoride (PVdF) binder as well as the air-stability, a self-assembled monolayer of 1H,1H–2H,2H-perfluorodecyltriethoxysilane (PFDTES) is introduced onto the surface of Ni-rich layered oxide cathode powder. A molecular functional monolayer with fluorocarbons on Ni-rich layered oxide powder is delivered to achieve an ∼ 13 Å thin homogeneous molecular-level functional coating at a negligible weight ratio. The functionalized surface improves the adhesion between PVdF and cathode powder by F⋯F interaction, relieving the electrode detachment. As a result, cycling failure mode is remarkably mitigated. The fluorinated hydrophobic surface alleviates water contamination, thereby reducing lithium impurities.

Induction and Maintenance of Local Structural Durability for High-Energy Nickel-Rich Layered Oxides.

Nickel-rich layered oxides are one of the most promising cathode candidates for next-generation high-energy-density lithium-ion batteries. However, due to similar ion radius between Li+ and Ni2+ (0.76 and 0.69Å), the Li+ /Ni2+ mixing phenomenon seriously hinders the migration of Li+ and increases kinetic barrier of Li+ diffusion, resulting in limited rate capability. In this work, the introduction of Ce4+ to effectively improve electrochemical properties of Ni-rich cathode materials is proposed. The LiNi0.8 Co0.15 Al0.05 O2 (LNCA) is modified with an additional precursor oxidization process using an appropriate amount of (NH4 )2 Ce(NO3 )6 . The Ce(NO3 )6 2- easily obtains electrons and generates reduction reactions, while Ni(OH)2 is prone to electron loss and oxidation reaction. The participation of (NH4 )2 Ce(NO3 )6 can promote the oxidation of Ni2+ to Ni3+ , thereby reducing the Li+ /Ni2+ mixing and increasing the structural stability of LNCA samples. Ce4+ cation doping can impede Li+ /Ni2+ mixing of LNCA cathode materials upon the long-term cycles. Both rate performance and long-term cyclability of Li[Ni0.8 Co0.15 Al0.05 ]0.97 Ce0.03 O2 (LNCA-Ce0.03) sample are significantly improved. Besides, a practical pouch cell based on the cathode presents sufficient gravimetric energy density (≈300Whkg-1 ) and cycling stability (capacity retention of 81.3% after 500 cycles at 1C).

Interfacial chemistry of vinylphenol-grafted PVDF binder ensuring compatible cathode interphase for lithium batteries

Elevating operating voltage is an effective route to further promote the energy density of nickel-rich layered oxides based lithium batteries. However, high-voltage cycling generally incurs rapid capacity fade of cells due to severe decomposition of commercially available liquid electrolytes and active material degradation. Especially, reactive oxygen species including 1O2 generated under high-voltage cycling give rise to severe electrolyte decomposition and thus result in fast capacity fading of batteries. To address this issue, herein, we first develop a vinylphenol-grafted PVDF binder with 1O2-scavenging effect for nickel-rich layered oxide cathodes, which is inspired by the eliminating role of dopamine. Detailed experiment research demonstrates that the scavenging behavior of the as-developed binder can help induce compatible cathode/electrolyte interface. Resultantly, the as-developed binder endows LiNi0.6Co0.2Mn0.2O2/Li and LiNi0.8Co0.1Mn0.1O2/Li half cells with superior cycling stability, with capacity retentions of 80.53% after 200 cycles and 87.16% after 100 cycles at 0.5C under 3.0–4.5 V, respectively. This dopamine-inspired strategy with reactive oxygen-scavenging effect heralds an important paradigm for constructing compatible cathode/electrolyte interphase in various rechargeable lithium cells.

In situ multiscale probing of the synthesis of a Ni-rich layered oxide cathode reveals reaction heterogeneity driven by competing kinetic pathways.

Nickel-rich layered oxides are envisaged as key near-future cathode materials for high-energy lithium-ion batteries. However, their practical application has been hindered by their inferior cycle stability, which originates from chemo-mechanical failures. Here we probe the solid-state synthesis of LiNi0.6Co0.2Mn0.2O2 in real time to better understand the structural and/or morphological changes during phase evolution. Multi-length-scale observations-using aberration-corrected transmission electron microscopy, in situ heating transmission electron microscopy and in situ X-ray diffraction-reveal that the overall synthesis is governed by the kinetic competition between the intrinsic thermal decomposition of the precursor at the core and the topotactic lithiation near the interface, which results in spatially heterogeneous intermediates. The thermal decomposition leads to the formation of intergranular voids and intragranular nanopores that are detrimental to cycling stability. Furthermore, we demonstrate that promoting topotactic lithiation during synthesis can mitigate the generation of defective structures and effectively suppress the chemo-mechanical failures.

Gradient doping Mg and Al to stabilize Ni-rich cathode materials for rechargeable lithium-ion batteries

Nickel-rich layered oxides are attracting extensive interest as cathode materials to build high-energy lithium-ion batteries, but their intrinsic structural instability and interfacial parasitic reactions deteriorate the cycling performance. Herein, we report concentration-gradient Mg and Al doped LiNi0.95Co0.03Al0.01Mg0.01O2 (NCAMg) as a stable and high-capacity cathode material. The obtained NCAMg microparticles exhibit outstanding cyclability (capacity retention of 95.6% after 100 cycles) and remarkable rate capability (172.9 mAh g−1 at 10 C). The gradient Mg and Al doping boosts the electrochemical performance by restraining the undesirable H2–H3 phase conversion and the anisotropic volume change. Moreover, the enrichment of Mg and Al at particle shell enhances the Li-ion diffusivity, inhibits the growth of microcracks, and significantly improves the thermal stability over LiNiO2. The results indicate that Mg and Al gradient co-doping is an efficient and practical route to upgrade Ni-rich layered oxide cathode materials for LIBs.