Tailoring the structural and morphological properties of LiNi0.5Co0.2Mn0.3O2 cathode materials via a novel mixed-solvothermal method

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

Understanding the influence of sulfur configuration on the electrochemical reaction pathway for lithium storage in molybdenum sulfides

The Li- and Mn-rich layered oxide cathode material class is a promising cathode material type for high energy density lithium-ion batteries. However, this cathode material type suffers from layer to spinel structural transition during electrochemical cycling, resulting in energy density losses during repeated cycling. Thus, improving structural stability is an essential key for developing this cathode material family. Elemental doping is a useful strategy to improve the structural properties of cathode materials. This work examines the influences of Mg doping on the structural characteristics and degradation mechanisms of a Li1.2Mn0.4Co0.4O2 cathode material. The results reveal that the prepared cathode materials are a composite, exhibiting phase separation of the Li2MnO3 and LiCoO2 components. Li2MnO3 and LiCoO2 domain sizes decreased as Mg content increased, altering the electrochemical mechanisms of the cathode materials. Moreover, Mg doping can retard phase transition, resulting in reduced structural degradation. Li1.2Mn0.36Mg0.04Co0.4O2 with optimal Mg doping demonstrated improved electrochemical performance. The current work provides deeper understanding about the roles of Mg doping on the structural characteristics and degradation mechanisms of Li-and Mn-rich layered oxide cathode materials, which is an insightful guideline for the future development of high energy density cathode materials for lithium-ion batteries.

The LiNi0.5Mn1.5O4 cathode material with high working voltage is a promising cathode material for next-generation lithium-ion batteries. In this investigation, LiNi0.5Mn1.5O4 materials with different particle sizes and crystal morphologies were synthesized by a modified solid-state method at different temperatures (750, 800, 850, and 900 °C). The evolution panorama of morphology and surface orientation with the temperature change of LiNi0.5Mn1.5O4 cathode materials were studied. The X-ray diffraction and scanning electron microscopy results showed that with the increase of temperature, the particle sizes increased and the crystal growth became more and more complete. Electrochemical tests showed that the material calcined under 850 °C exhibits a truncated octahedral structure and the best electrochemical performance. It delivers a discharge capacity of 124 mA h g−1 at 1 C; even at a high rate of 10 C, a capacity of 90 mA h g−1 can be obtained. The discharge capacity retention of the material is 91.2% after 150 cycles. In addition, the sample prepared by acetate reactant shows excellent electrochemical performance due to the truncated octahedron structure consisted of {111} and {100} surface as well as the appropriate particle size of ~ 1 μm. The {111} surface is conducive to stabilize the material structure, and {100} surface is conducive to the transfer of Li+ ion and electrons. At the same time, it also founded that the appropriate particle size could reduce the electrolyte corrosion of the material and easy for Li+ ion migration. As a result, the material exhibits an improved electrochemical performance.

Synthesis of Li2Si2O5-coated LiNi0.6Co0.2Mn0.2O2 cathode materials with enhanced high-voltage electrochemical properties for lithium-ion batteries

PVP-bridged γ-LiAlO2 nanolayer on Li1.2Ni0.182Co0.08Mn0.538O2 cathode materials for improving the rate capability and cycling stability

Many synthesis techniques like sol-gel, co-precipitation, hydrothermal, pyrolysis, and many more have been used to synthesize batteries' active electrode materials. High surface area cathode materials with smaller nanoparticles are favored for their higher reactivity compared to materials with particles of larger size. Sol-gel and co-precipitation methods have been primarily adopted because they can produce the desirable particle size easily and on a large scale. This dissertation details an efficient and cost-effective process for using a newly developed sol-gel method that uses glycerol solvent instead of the conventionally used water. Glycerol has three hydroxyl groups (OH) instead of one in water. These can play an important role in nanoparticle formation at earlier stages by speeding up the reaction. One of the main reasons for capacity fade in batteries is cationic mixing between Ni2+ and Li+. This results in blocking of the Li+ path and ultimately poor cyclability. This capacity fade has been successfully minimized in our current work by taking advantage of the high heat released from glycerol to get partially crystalline nanoparticles that could mitigate cationic mixing at high temperatures. The first cathode material synthesized using glycerol solvent was LiMn1/3Ni1/3Co1/3O2 (LMNC) layered oxide cathode material. Temperature's effects on the particles' morphologies, sizes, and electrochemical performances have been studied at four different temperatures. LMN2 was annealed at 900 �C/8hr and shows desirable particles size of ~ 0.3 (�_m), an initial discharge capacity of 177.1 mAh/g in the first cycle, and a superior capacity retention of 83.7% after 100 cycles. The process takes eight hours, rather than >12hr when using other solvents to prepare LMNC material at high temperatures. The results also demonstrate the higher stability and lower cationic mixing after 100 cycles. To increase capacity and voltage, lithium-rich cathode materials with the formula Li1.2Mn0.51Ni0.145+xCo0.145-xO2 (x = 0 (LR2), 0.0725 (LR1)) have been successfully synthesized. In this material, cobalt (Co) content has been decreased by half and the larger produced particles have suppressed the total activation of Li2MnO3 phase in the first charge cycle. The specific discharge capacity retention of LR1 at 1C between 2 and 4.8 V was more than 100% after 100 cycles. Further improvements to LR1 cathode materials have led to an increase in the initial discharge capacity to 248 mAh/g at 0.1C. This is achieved by using an equimolecular combination of acetate and nitrate salt anions (LRACNI) with cornstarch. Cornstarch acts as a capping agent with the nitrate salt anions, and a gelling agent with acetate based anions. LRACNI shows an intermediate particle size with satisfactory capacity retention upon cycling and the lowest cationic mixing. LiNi0.8Co0.15Al0.05O2 (NCA) is one of the most commercialized cathode materials for lithium-ion batteries. It is challenging to have a high Ni content with Li in one combination electrode because cationic mixing increases proportionally. The use of glycerol has diminished the cationic mixing. High capacity retentions of 97% at 1C after 50 cycles, 87.6% at 0.3C after 100 cycles, and 93.6% at 0.1C after 70 cycles have been successfully achieved, which are better than those previously reported.

The role of boracic polyanion substitution on structure and high voltage electrochemical performance of Ni-Rich cathode materials for lithium ion batteries

Integrated co-modification of PO43− polyanion doping and Li2TiO3 coating for Ni-rich layered LiNi0.6Co0.2Mn0.2O2 cathode material of Lithium-Ion batteries

The effect of drying methods on the structure and performance of LiNi0.5Co0.2Mn0.3O2 cathode material for lithium-ion batteries

Hydrothermal preparing agglomerate LiNi0.8Co0.1Mn0.1O2 cathode material with submicron primary particle for alleviating microcracks

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

Lithium-ion conductor LiAlO2 coated LiNi0.8Mn0.1Co0.1O2 as cathode material for lithium-ion batteries

As a result of its substantial energy density, layered LiNi0.8Co0.15Al0.05O2 cathode materials are thought to be the most promising of the next-generation cathode materials for electric vehicles (EVs). In this research, self propagating combustion (SPC) is used to prepare cathode materials made of pristine LiNi0.8Co0.15Al0.05O2 (NCA) and NCA doped with 1% Fe to produce LiNi0.8Co0.14Fe0.01Al0.05O2. Based on X-Ray Diffraction (XRD) results, pristine and doped NCA cathode materials were pure and single phase. Reference Intensity Ratio (RIR) values for pristine and doped NCA are 0.87 and 1.12 respectively indicating that the amount of cation mixing was reduced with Fe doping. Through Rietveld refinement, it was discovered that the addition of Fe to NCA resulted in a decrease in cation mixing from 13.56% to 4.07%.It was found that both pristine and doped NCA possessed polyhedral like shape morphology. It can be seen that doping with 1% Fe does not change much in the crystallite size of the materials. By having less cation mixing, Fe doped was found to greatly improve the structural integrity of NCA cathode materials, which in turn improved the materials’ electrochemical performance.

The Na-doped layer-structured Li1−x Na x Ni1/3Co1/3Mn1/3O2 (x = 0, 0.01, 0.03, 0.05, 0.07) cathode materials for lithium-ion batteries have been successfully synthesized by co-precipitation reaction combined with solid-state sintering method. The structure and morphologies of cathode materials Li1−x Na x Ni1/3Co1/3Mn1/3O2 (x = 0, 0.01, 0.03, 0.05, 0.07) were measured by the powder X-ray diffraction, a field emission scanning electron microscope, energy-dispersive spectrometer, energy-dispersive X-ray spectroscopy and transmission electron microscope. The electrochemical performances were measured by galvanostatic charge–discharge test at different rates, electrochemical impedance spectroscopy and cyclic voltammetry. Compared with pristine sample, the Na-doped cathode materials have higher discharge specific capacity, more excellent cycling stability and better rate performance. The sample of Li0.95Na0.05Ni1/3Co1/3Mn1/3O2 has the most excellent electrochemical performances. It exhibits 204.5 m Ahg−1 initial discharge specific capacity and 87.2% capacity retention after 30 cycles at 0.1 C in the voltage range of 3.0–4.8 V. While the pristine LiNi1/3Co1/3Mn1/3O2 material illustrates 187.1 m Ahg−1 initial discharge specific capacity and 78.4% capacity retention after 30 cycles at 0.1 C in the voltage range of 3.0–4.8 V.