One of the major hurdles of Ni‐rich cathode materials Li1+x(NixCozMnz)wO2, y > 0.5 for lithium‐ion batteries is their low cycling stability especially for compositions with Ni ≥ 60%, which suffer from severe capacity fading and impedance increase during cycling at elevated temperatures (e.g., 45 °C). Two promising surface and structural modifications of these materials to alleviate the above drawback are (1) coatings by electrochemically inert inorganic compounds (e.g., ZrO2) or (2) lattice doping by cations like Zr4+, Al3+, Mg2+, etc. This paper demonstrates the enhanced electrochemical behavior of Ni‐rich material LiNi0.8Co0.1Mn0.1O2 (NCM811) coated with a thin ZrO2 layer. The coating is produced by an easy and scalable wet chemical approach followed by annealing the material at ≥700 °C under oxygen that results in Zr doping. It is established that some ZrO2 remains even after annealing at ≥800 °C as a surface layer on NCM811. The main finding of this work is the enhanced cycling stability and lower impedance of the coated/doped NCM811 that can be attributed to a synergetic effect of the ZrO2 coating in combination with a zirconium doping.

In this work, nickel-rich, layered-structure LiNi 0.65 Co 0.08 Mn 0.27 O 2 cathode materials were synthesized and compared with materials of the same overall composition, but with a concentration gradient throughout the particles: the Ni concentration is higher at the center of the particles and lower at surface, while the opposite is true for the Mn concentration. The co-precipitation synthesis parameters were optimized, with two different annealing protocols for the final products and the effect of chelating agent concentration during synthesis examined. The gradient materials provided superior capacity and rate capability than their respective non-gradient materials, at normal operating potentials and temperatures, e.g. 30 • C up to 4.3 V vs. Li. The reasons for the improved discharge capacity of the gradient materials were explored through impedance spectroscopy and post-mortem characterization. The gradient structure evolution was examined via TEM and electron diffraction measurements of particle cross-sections. Prolonged cycling, even at elevated temperatures, did not change the initial concentration profiles determined by the synthesis. Additionally, long-term cycling experiments of the second-generation material electrodes vs. graphite electrodes in full cells were performed in order to explore the practical advantage of these novel materials.

Layered structure transition metal oxides of the form LiNixCoyMnzO2  (x + y + z = 1), are commercially available lithium ion battery materials that provide capacities of 140 – 200 mAhrg-1  over long lifetimes, ca. 3000 cycles with 80 % capacity retention. The composition of these materials can be used to tailor specific properties such as capacity, cycle life, low impedance, toxicity or cost. In order to enhance capacity and average operating voltage fade, Ni rich materials (x ≥ 0.65), can be used, but surface Ni-oxide and hydroxide moieties are highly alkaline, tending to react strongly with the standard electrolyte solutions, what limits the electrodes’ cycle life. One method to increase cycle life of electrodes, comprising Ni-rich material, is to synthesize materials with a low Ni surface content and high Ni concentration at the core. It is possible to synthesize Li[NiCoMn]O2 materials with Ni and Mn concentration gradients. Many different gradient variables may be explored, for example thickness of core and shell, differences between surface and bulk concentrations and the structure of the  gradient, e.g. linear, exponential, single or multiphase. For our work, we have synthesized cathode materials utilizing the coprecipitation method, exploring first different annealing protocols to produce Ni-rich LiNi0.65Co0.08Mn0.27O2. After optimization of the annealing conditions, we have monitored the effect of metal chelation agent concentration on the electrochemical performance of the battery material. Then, we explore an even more nickel-rich gradient material, the LiNi0.7Co0.1Mn0.2O2, also introducing a two-phase gradient with two distinct Ni/Mn concentration slopes. The materials are cycled in both half cells (vs. Li) and full cells vs. graphite, to explore short term and long term effects, respectively. Electrochemical impedance spectroscopy is utilized to monitor the evolution of surface film impedance during cycling. High temperature (up to 60 oC) cycling and mean discharge voltage stability are studied, exhibiting the enhanced stabilizing effects of the Ni/Mn gradients. In addition, bulk and surface changes such as the alteration of the gradient structure after prolonged cycling is explored via TEM and electron diffraction measurements. The extent of transition metal ions dissolution is measured by chemical analysis of anodes, removed after cycling, on which the metals are partially reduced. Figure 1 depicts typical galvanostatic cycling results of LiNi0.65Co0.08Mn0.27O2 vs. graphite full cells at hard conditions: high rate and elevate temperature, demonstrating an advantage to the cathode material with gradient concentration.  The entire study have proven that for Ni rich Li[NiCoMn]O2 cathode materials, the concentration gradient enables a better performance compared to similar cathode materials with uniform concentration. Figure 1: Galvanostatic cycling of  gradient (FCGT, red) and standard, non-gradient (CC, black) cathode materials at high rates (2C for 29 cycles, then 1 cycle at C/10, repeated), at 45 oC  vs. graphite full cells. Figure 1

In this presentation, we report on studies of novel positive electrode materials for lithium-ion batteries with the main emphasis on their structural and surface modifications by cation doping and coating. We have chosen three families of materials: Li- and Mn-rich high-energy density and high capacity (HE-NCM)(1), Ni-rich layered materials Li[NixCoMn]O2 (x>0.5),(2) and gradient materials of the general formulae of LiNi0.65Co0.08Mn0.27O2 . Al3+ and other cations as dopants(3) and salts such as AlF3 as  coating materials were studied(4). We have demonstrated the impact of a minor level of Al-doping on the electrochemical characteristics of LiNi0.5Co0.2Mn0.3O2 electrodes and on the interfacial reactions.(4) We propose that the lower capacity fading of the Al-doped electrodes upon aging of the cells in a charged state (4.3 V) at 60 0C in comparison with their undoped counterparts, as well as more stable mean voltage behavior, are likely due to the chemical and structural modifications of the electrode/solution interface. The lower electrochemical impedance of Al-doped LiNi0.5Co0.2Mn0.3O2 electrodes can be explained by more stable surface chemistry developed on the doped particles due to the interfacial reactions of the dopant in Al3+ enriched surface layer (“segregated” aluminum) with an EC-EMC/LiPF6 solution. The modified interface on the Al-doped particles is less resistive and comprises the Li+-ion conducting nano-sized centers like AlF3, which promote Li+ ionic transport to the bulk.             Furthermore, we present our recent results on the study of Ni-rich, layered-structure LiNi0.65Co0.08Mn0.27O2 cathode materials and compare their electrochemical performance with materials of the same overall composition, but with a concentration gradient throughout the particles. The gradient was organized as follows: the Ni concentration is higher at the center of the particles but lower at surface, while the Mn concentration is higher at the surface and lower at the center. The synthesis parameters of the co-precipitation method were optimized comparing annealing periods, followed by electrochemical testing. Three different sets of gradient and standard non-gradient materials were explored, and all gradient materials provided superior capacity and rate capability than their respective non-gradient materials. The reasons for the improved discharge capacity of the gradient materials at moderate temperatures and cut-off potentials were explored through impedance spectroscopy and post-mortem characterization. The Mn-rich surface of the gradient material limits the growth of too resistive surface films during cycling, even at extreme temperatures and potentials, improving stability of these cathode materials. The evolution of the gradient structure was examined via TEM and EDX of FIB-produced particle cross-sections. We have established that prolonged cycling, even at elevated temperatures, did not change the initial concentration profiles determined by the synthesis. Transition metal ion dissolution from the cathode was confirmed via ICP of dissolved Li metal anodes, showing a greater degree of Mn dissolution from the non-gradient materials, possibly due to nickel-manganese segregation tendencies. This greater degree of Mn dissolution from non-gradient materials was confirmed in EDX of cycled particles. Electron diffraction measurements of these cycled particles show that spinel formation during cycling of the gradient materials is limited or even eliminated likely due to the higher concentration of Ni in the bulk of the gradient materials opposed to the non-gradient materials. Finally, we demonstrate long-term, (>1000 cycles) experiments of the gradient material electrodes vs. graphite electrodes in full cells that were performed in order to explore the practical advantage of these materials. 1.         P. K. Nayak, J. Grinblat, M. Levi, B. Markovsky and D. Aurbach, Journal of the Electrochemical Society, 161, A1534 (2014). 2.         C. Ghanty, B. Markovsky, E. M. Erickson, M. Talianker, O. Haik, Y. Tal-Yossef, A. Mor, D. Aurbach, J. Lampert, A. Volkov, J.-Y. Shin, A. Garsuch, F. F. Chesneau and C. Erk, Chemelectrochem, 2, 1479 (2015). 3.         D. Aurbach, O. Srur-Lavi, C. Ghanty, M. Dixit, O. Haik, M. Talianker, Y. Grinblat, N. Leifer, R. Lavi, D. T. Major, G. Goobes, E. Zinigrad, E. M. Erickson, M. Kosa, B. Markovsky, J. Lampert, A. Volkov, J.-Y. Shin and A. Garsuch, Journal of the Electrochemical Society, 162, A1014 (2015). 4.         F. Amalraj, M. Talianker, B. Markovsky, L. Burlaka, N. Leifer, G. Goobes, E. M. Erickson, O. Haik, J. Grinblat, E. Zinigrad, D. Aurbach, J. K. Lampert, J.-Y. Shin, M. Schulz-Dobrick and A. Garsuch, Journal of the Electrochemical Society, 160, A2220 (2013).