Electrochemical Performance Of Li1 Research Articles

Electrochemical properties of Li-rich ternary cathode material Li1.20Mn0.44Ni0.32Co0.04O2 and its oxygen-deficient phase

As the cathode material of lithium-ion batteries, Li-rich ternary layered oxides usually suffer from high first cycle irreversible capacity, low rate capability, and structural instability during charge–discharge. Recent studies show that Ni-rich Li1.20Mn0.44Ni0.32Co0.04O2 material has good structural stability. In this paper, the electrochemical performance of Li1.20Mn0.44Ni0.32Co0.04O2 and its oxygen-deficient phase Li1.20Mn0.44Ni0.32Co0.04O1.83 are studied by the first-principles calculations. The results show that, for the pristine phase Li1.20Mn0.44Ni0.32Co0.04O2, the theoretical delithiation capacity is 380 mAh/g and the highest charging voltage platform is 4.99 V. The O ions are found to participate in the charge compensation significantly. Ni ions can only contribute 118 mAh/g of the delithiation capacity, and the remaining charging capacity is contributed by O ions. For the oxygen-deficient phase Li1.20Mn0.44Ni0.32Co0.04O1.83, the highest voltage platform is reduced by 0.21 V, O ions are also found to participate in the charge compensation obviously. Compared to the pristine phase, transition metal (TM) ions in the oxygen-deficient phase exhibit higher chemical activity, while the contribution of O ions to charge compensation is relatively reduced. The oxygen-deficient phase has a slightly higher theoretical capacity (392 mAh/g) than the pristine phase.

Effects of lithium content on the electrochemical performance of Li1+xV3O8 cathode materials for lithium-ion batteries

Lithium trivanadate (LiV3O8) is of great interest due to its large capacity, low cost and easy preparation. However, it still suffers from an inferior cyclability and rate capability. To solve these shortcomings of LiV3O8, a small extra amount of lithium was introduced into Li sites of LiV3O8. Herein, Li-doped LiV3O8 (Li1+xV3O8) materials were prepared and the electrochemical performance of Li1+xV3O8 changes with x from 0 to 0.1, 0.2 and 0.3. The discharge capacity of Li1+xV3O8 increases from x = 0 to 0.2 and then decreases, and the change trend of cycle performance is the same as that of discharge capacity. The optimal Li-doped LiV3O8 sample, Li1.2V3O8, exhibits much higher capacity and better cyclability and rate capability than LiV3O8. Galvanostatically discharged and charged between 2.0 and 4.0 V, Li1.2V3O8 and LiV3O8 present the initial discharge capacities of 305 and 268 mAh g−1 at 0.1 C (30 mA g−1), respectively, and the corresponding capacity retentions are 87% and 80% after 50 cycles. Even at a high current rate of 2 C, Li1.2V3O8 exhibits high discharge capacity of 173 mAh g−1, much higher than the discharge capacity of 133.6 mAh g−1 for LiV3O8. The better electrochemical performance of Li1.2V3O8 can be ascribed to the doping of appropriate amount of Li+ in LiV3O8 and the resulted higher diffusion coefficients of Li+ in Li1.2V3O8.

Understanding the mechanism of performance difference when substituting Al for different transition metal ions in Li-rich Mn-based cathode materials

The Al-doped modification strategy by substituting Al for different transition metal ions (TMs, TM = Mn, Ni, Co) has achieved excellent results in improving the cyclic performance of Li-rich Mn-based cathode materials (LRMs). However, the traditional explanation known as “pegging effect” is hard to distinguish how Al works in different TM substitutions. Herein, the electrochemical performances of Li1.2Mn0.52Ni0.13Co0.13Al0.02O2 (LRM-Mn), Li1.2Mn0.54Ni0.11Co0.13Al0.02O2 (LRM-Ni) and Li1.2Mn0.54Ni0.13Co0.11Al0.02O2 (LRM-Co) are studied, and LRM-Mn shows the superior long-term cycling stability, especially at the high temperature of 55 °C. Density functional theory (DFT) reveals that LRM-Mn crystal structure has higher thermodynamic stability than any other sample, which is advantageous for inhibiting the transition of LRMs to low-energy stable phases during cycling (e.g., spinel phase and rock salt phase). Combined with density of states and Bader charge analyses, we think that the increased thermodynamic stability of LRM-Mn results from the reduction of the charge transfer of Mn and Co ions in a single delithiation process, which lowers the reactivity of TMs, alleviates the Li/TM mixing and inhibits the irreversible oxygen release. In addition, the biggest volume change during the delithiation process was observed when Al was substituted for Co, which results in the materials’ premature production of fatigue stresses and intergranular cracking. This work comprehensively explains the modification mechanism of Al-doped in LRMs. It demonstrates practical significance for both the rational design of materials and the electrode electrochemical performance prediction.

Elucidating the Role of Excess Li in the Electrochemical Performance of Li1+x[Ni0.5Mn0.5]1−xO2 Layered Oxides

Layered cathode materials comprising of Ni and Mn can possess comparable theoretical capacities to Ni-rich cathode materials. However, to draw upon this capacity, they need to overcome rate capability issues and operate to higher voltages. Incorporating excess Li during synthesis can allow much of this capacity to be accessed. This work compares the effects of excess Li on electrochemical properties of Li1+x[Ni0.5Mn0.5]1-xO2 layered oxides in the conventional voltage window as well as with higher upper cut-off voltages. Materials with different amounts of excess Li were systematically compared based on specific capacity, first-cycle irreversible loss, cycling stability, and rate capability in the voltage ranges of 3.0 V–4.3 V, 3.0 V–4.5 V, and 3.0 V–4.8 V. In all samples, excess Li improves the rate capability and cycling stability in all these voltage ranges while significant gains in specific capacity can only be attained when operating these materials at higher voltage cut-offs. The improved rate capability performance in presence of excess Li can be attributed to enhanced electronic conductivity and Li+ ion diffusion arising from reduced amounts of Ni in the Li layer.

Effect of FePO4 coating on structure and electrochemical performance of Li1.2Ni0.13Co0.13Mn0.54O2 as cathode material for Li-ion batteries

Effect of FePO4 coating on structure and electrochemical performance of Li1.2Ni0.13Co0.13Mn0.54O2 as cathode material for Li-ion batteries

(Digital Presentation) Cobalt Free Cathode Synthesized By Sacrificial Template (α-MnOOH) for Rechargeable Lithium Batteries

LiCoO2 cathode has been used widely for Li-ion batteries (LIBs) for portable applications due to it is compactness, high energy density, excellent cycle life and reliability [1]. Nevertheless, the high cost of cobalt represent some of the limitations of this material [1]. As an alternative, LiNiO2, which iso-structural with LiCoO2, is reported as a stable material for LIB cathodes. Although, the poor thermal stability of this material in operating LIB represents safety risk [2]. On the other hand, LiMnO2 has also been proposed as a low-cost cathode for LIB. However, it is not stable during charging/discharging processes [3]. Ni-rich layer oxide (LiM1-x NxiO2, where M is a transition metal, x > 0.8) appeared as result of much effort dedicated for finding an adequate balance between cost and stability [4]. In comparison to Ni-rich layer, Li-rich layer oxide exhibited better cyclability and safety performance at higher electrode potentials (>4.5 V vs. Li|Li+) [4]. However, the structural and electrochemical properties of the as-prepared materials are determined by the synthesis methods and/or preparation conditions [5]. For instance, the electrochemical performance of Li1.5Ni0.25Mn0.75O2.5 layer material obtained by a simple carbonate coprecipitation method was improved with 240 mAh g-1 and 70.3% of capacity retention after 30 cycles at 0.05C [6].In this work, we report the feasibility of producing a cobalt free cathode LiNi0.5Mn0.5O2 with high energy density using a sacrificial template α -MnOOH as precursor with a simple balance between lithium and nickel content. The synthesis strategies performed in this work led to a promising cathode material with high energy density without sacrificing the operating voltage window, by combining our understanding of the factors governing the cation order with a facile synthetic route that ensured good cation mixing.The LiNi0.5Mn0.5O2 active cathode material was produced by co-precipitated method according to the following procedure: α-MnOOH sacrificial template was synthesized according to ref. [7].Then active cathode material was obtained by co-precipitation method using α-MnOOH, lithium acetate and nickel acetate with a molar ratio of 0.5:1.05:0.5 mol at different treatment temperatures (700°C, 800°C and 900°C). Rate capabilities of all samples are displayed in Fig. 1. The charge-discharge current was increased from 20 mA g-1 (0.1C) to 2000 mA g-1 (10C), and then decreased back to 20 mA g-1. The Li1.05Ni0.5Mn0.5O2 material displayed the best electrochemical performance at 800°C which the initial discharge capacity was 179.9 mAh g-1 . The other samples at 700 °C and 900 °C showed initial discharge capacities of 171.3 mAh g-1 and 156.4 mAh g-1 at 0.1C, respectively. On the other hand, α-MnOOH sacrificial template synthesis showed to be a plausible formation mechanism and the structure–function relationships of LiNi0.5Mn0.5O2.[1] N. Nitta, F. Wu, J. T. Lee, and G. Yushin, “Li-ion battery materials: present and future,” Mater. Today, vol. 18, no. 5, pp. 252–264, Jun. 2015.[2] M. Bianchini, M. Roca-Ayats, P. Hartmann, T. Brezesinski, and J. Janek, “There and Back Again—The Journey of LiNiO2 as a Cathode Active Material,” Angew. Chemie Int. Ed., vol. 58, no. 31, pp. 10434–10458, Jul. 2019.[3] T. Ohzuku and Y. Makimura, “Layered Lithium Insertion Material of LiNi 1/2 Mn 1/2 O 2 : A Possible Alternative to LiCoO 2 for Advanced Lithium-Ion Batteries,” Chem. Lett., vol. 30, no. 8, pp. 744–745, Aug. 2001.[4] G. Hu et al., “A facile cathode design with a LiNi0.6Co0.2Mn0.2O2 core and an AlF3-activated Li1.2Ni0.2Mn0.6O2 shell for Li-ion batteries,” Electrochim. Acta, vol. 265, pp. 391–399, Mar. 2018.[5] C. Zhao, X. Wang, R. Liu, F. Xu, and Q. Shen, “β-MnO2 sacrificial template synthesis of Li 1.2Ni0.13Co0.13Mn0.54O2 for lithium ion battery cathodes,” RSC Adv., vol. 4, no. 14, pp. 7154–7159, Jan. 2014.[6] M. Akhilash, P. S. Salini, K. Jalaja, B. John, and T. D. Mercy, “Synthesis of Li1.5Ni0.25Mn0.75O2.5 cathode material via carbonate co-precipitation method and its electrochemical properties,” Inorg. Chem. Commun., vol. 126, p. 108434, Apr. 2021.[7] F. A. Vásquez, J. E. Thomas, A. Visintin, and J. A. Calderón, “LiMn1.8Ni0.2O4 nanorods obtained from a novel route using α-MnOOH precursor as cathode material for lithium-ion batteries,” Solid State Ionics, vol. 320, pp. 339–346, Jul. 2018. Figure 1

Improved Capacity Retention for a Disordered Rocksalt Cathode via Solvate Ionic Liquid Electrolytes

AbstractLithium‐rich disordered rocksalts (DRX) are a promising class of cathode materials for high‐energy lithium ion batteries (LIBs) and lithium metal batteries (LMBs) due to the high initial specific capacities (>200 mAh g−1) as well as flexible chemical composition. However, challenges concerning severe capacity fade and voltage decay upon cycling at high cut‐off voltages are still to be overcome. Moreover, state‐of‐the‐art carbonate‐based electrolytes can be decomposed by reactive oxygen species released by DRX materials during cycling. In this work, the electrochemical performance of Li1.25Fe0.5Nb0.25O2 (LFNO) || Li LMB and LFNO || graphite LIB cells is compared for a conventional, carbonate‐based electrolyte and the solvate ionic liquid (SIL) [Li(G3)][TFSI] (G3: triethyleneglycoldimethylether). Cycle life is notably improved by the chemically more stable ionic liquid electrolyte, as the anionic redox activity of LFNO is prolonged compared to the carbonate‐based cells. This work represents an important step toward an improved cycle life of DRX cathodes.

Effect of Na Doping on the Electrochemical Performance of Li1.2Ni0.13Co0.13Mn0.54O2 Cathode for Lithium-Ion Batteries

This study aims to investigate the effect of Na doping on the structure, electrical, and electrochemical properties of lithium-rich cathode material. Pristine Li1.2Ni0.13Mn0.54Co0.13O2 (LNMC) and Na-doped Li1.17Na0.03Ni0.13Mn0.54Co0.13O2 (Na-LNMC) layered lithium-rich/manganese-rich compounds are prepared by the sol-gel method. The structural and morphological characterization reveals that the Na doping leads to an ordered structure with regular cubic morphology and enlarged Li layer spacing. This enlargement facilitates the diffusion of lithium ion inside the bulk lattice. Electrochemical impedance spectroscopy (EIS) shows that doping by a small amount of Na (3 mol%) decreases the impedance by more than three orders of magnitude and enhances the diffusion of lithium ions in the same proportion. This remarkable improvement in the conductivity and diffusion coefficient of lithium ions of Na-LNMC improves its capacity retention. In addition, this structure and mode of preparation results in “U-shaped” capacity vs. cycle curves, similar to the curves observed for transition metal oxide electrodes, resulting in an exceptional cycle life, tested for up to 400 cycles at 2C.

Combustion synthesis and characterization of Li1.2Mn0.52Ni0.20Co0.08O2 cathodes for Li-Ion battery: Effect of fuel mixture and annealing temperature

The effect of fuel mixture and annealing temperature on the structural properties and electrochemical performance of Li1.20Mn0.52Ni0.20Co0.08O2 powders prepared by the combustion synthesis were studied. Different combinations of citric acid fuel and ammonium acetate along with post-temperature treatments could be used to control the product characteristics. Simultaneous thermal analyses and thermodynamic modelling were used to describe the combustion processes. The analysis of the XRD data and other reports showed that the synthesis method and chemical compositions of lithium-rich layered oxides (LLO) could influence their description either as a solid solution or a ‘composite’ structure. The annealing temperature greatly influenced the lattice parameters, unit cell volumes, crystallite sizes, and cationic disorder of the samples whilst the use of fuel mixture had little effect. Furthermore, the electrochemical performances of the cathode materials were studied and the relationship with the structural properties of the powder samples were analysed. The Li1.20Mn0.52Ni0.20Co0.08O2 powders synthesized with only citric acid fuel (100-T) displayed the best electrochemical performance compared with those produced using the fuel mixtures. The enhanced electrochemical performance of the 100-T cathodes was shown to be an integrative property of the highest values reported for their structural properties. The results show that citric acid assisted combustion and annealing temperature (mostly with pre-annealing) could be used to optimize the electrochemical performance of LLO cathode materials.

Cobalt Free Cathode Synthesized By Sacrificial Template (α-MnOOH) for Rechargeable Lithium Batteries

Cobalt Free Cathode Synthesized by Sacrificial Template (α -MnOOH) for Rechargeable Lithium Batteries LiCoO2 cathode has been used widely for Li-ion batteries (LIBs) for portable applications due to it is compactness, high energy density, excellent cycle life and reliability [1]. Nevertheless, the high cost of cobalt represent some of the limitations of this material [1]. As an alternative, LiNiO2, which iso-structural with LiCoO2, is reported as a stable material for LIB cathodes. Although, the poor thermal stability of this material in operating LIB represents safety risk [2]. On the other hand, LiMnO2 has also been proposed as a low-cost cathode for LIB. However, it is not stable during charging/discharging processes [3]. Ni-rich layer oxide (LiM1-x NxiO2, where M is a transition metal, x > 0.8) appeared as result of much effort dedicated for finding an adequate balance between cost and stability [4]. In comparison to Ni-rich layer, Li-rich layer oxide exhibited better cyclability and safety performance at higher electrode potentials (>4.5 V vs. Li|Li+) [4]. However, the structural and electrochemical properties of the as-prepared materials are determined by the synthesis methods and/or preparation conditions [5]. For instance, the electrochemical performance of Li1.5Ni0.25Mn0.75O2.5 layer material obtained by a simple carbonate coprecipitation method was improved with 240 mAh g-1 and 70.3% of capacity retention after 30 cycles at 0.05C [6].In this work, we report the feasibility of producing a cobalt free cathode LiNi0.5Mn0.5O2 with high energy density using a sacrificial template α -MnOOH as precursor with a simple balance between lithium and nickel content. The synthesis strategies performed in this work led to a promising cathode material with high energy density without sacrificing the operating voltage window, by combining our understanding of the factors governing the cation order with a facile synthetic route that ensured good cation mixing.The LiNi0.5Mn0.5O2 active cathode material was produced by co-precipitated method according to the following procedure: α-MnOOH sacrificial template was synthesized according to ref. [7].Then active cathode material was obtained by co-precipitation method using α-MnOOH, lithium acetate and nickel acetate with a molar ratio of 0.5:1.05:0.5 mol at different treatment temperatures (700°C, 800°C and 900°C). Rate capabilities of all samples are displayed in Fig. 1. The charge-discharge current was increased from 20 mA g-1 (0.1C) to 2000 mA g-1 (10C), and then decreased back to 20 mA g-1. The Li1.05Ni0.5Mn0.5O2 material displayed the best electrochemical performance at 800°C which the initial discharge capacity was 179.9 mAh g-1 . The other samples at 700 °C and 900 °C showed initial discharge capacities of 171.3 mAh g-1 and 156.4 mAh g-1 at 0.1C, respectively. On the other hand, α-MnOOH sacrificial template synthesis showed to be a plausible formation mechanism and the structure–function relationships of LiNi0.5Mn0.5O2.[1] N. Nitta, F. Wu, J. T. Lee, and G. Yushin, “Li-ion battery materials: present and future,” Mater. Today, vol. 18, no. 5, pp. 252–264, Jun. 2015.[2] M. Bianchini, M. Roca-Ayats, P. Hartmann, T. Brezesinski, and J. Janek, “There and Back Again—The Journey of LiNiO2 as a Cathode Active Material,” Angew. Chemie Int. Ed., vol. 58, no. 31, pp. 10434–10458, Jul. 2019.[3] T. Ohzuku and Y. Makimura, “Layered Lithium Insertion Material of LiNi 1/2 Mn 1/2 O 2 : A Possible Alternative to LiCoO 2 for Advanced Lithium-Ion Batteries,” Chem. Lett., vol. 30, no. 8, pp. 744–745, Aug. 2001.[4] G. Hu et al., “A facile cathode design with a LiNi0.6Co0.2Mn0.2O2 core and an AlF3-activated Li1.2Ni0.2Mn0.6O2 shell for Li-ion batteries,” Electrochim. Acta, vol. 265, pp. 391–399, Mar. 2018.[5] C. Zhao, X. Wang, R. Liu, F. Xu, and Q. Shen, “β-MnO2 sacrificial template synthesis of Li 1.2Ni0.13Co0.13Mn0.54O2 for lithium ion battery cathodes,” RSC Adv., vol. 4, no. 14, pp. 7154–7159, Jan. 2014.[6] M. Akhilash, P. S. Salini, K. Jalaja, B. John, and T. D. Mercy, “Synthesis of Li1.5Ni0.25Mn0.75O2.5 cathode material via carbonate co-precipitation method and its electrochemical properties,” Inorg. Chem. Commun., vol. 126, p. 108434, Apr. 2021.[7] F. A. Vásquez, J. E. Thomas, A. Visintin, and J. A. Calderón, “LiMn1.8Ni0.2O4 nanorods obtained from a novel route using α-MnOOH precursor as cathode material for lithium-ion batteries,” Solid State Ionics, vol. 320, pp. 339–346, Jul. 2018. Figure 1

Synthesis and electrochemical properties of high power Li1+xV3O8 cathode materials for lithium-ion batteries

Monoclinic Li1+xV3O8 cathode materials were synthesized by sol-gel method. The structure, morphology and electrochemical performance of Li1+xV3O8 are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. Moreover, the effects of content of lithium on the physical and electrochemical properties of Li1+xV3O8 cathode materials are studied. The results show that the Li1.2V3O8 cathode material prepared by sol-gel method has good electrochemical properties, which has an initial discharge and charge specific capacities of 279.7 and 305 mAh g−1 at the current of 50 ​mA ​g−1 between 1.5 and 4.0 ​V, respectively, and a good cycle performance. In addition, the Li1.2V3O8 cathode material also has a good rate performance.

Impact of LiTi2(PO4)3 coating on the electrochemical performance of Li1.2Ni0.13Mn0.54Co0.13O2 using a wet chemical method

NASICON-type solid-state electrolyte has been reported to improve the structural and electrochemical stability of high nickel positive electrode materials; however, the impact of NASICON-type solid-state electrolyte on the performance of lithium-rich cathode has been barely studied. In this work, various contents of LiTi2(PO4)3 (LTP)-coated Li1.2Ni0.13Mn0.54Co0.13O2 have been made via a wet chemical method followed by sintering at 550 °C for 3 h. Those modified materials failed to show improvement in electrochemical properties including specific capacity, coulombic efficiency (CE), rate capability, and cycle life compared with uncoated material. Thick LTP coating even decreases the average discharge voltage and increases the impedance and voltage hysteresis of cells. XRD, TEM, and SAED images revealed non-uniform coating with multiple components including LiTi2(PO4)3, TiP2O7, and TiO2. This work suggests LTP coating on Li1.2Ni0.13Mn0.54Co0.13O2 using a wet chemical method might be challenging and need to be carefully carried out.

Fe3+ and PO43- co-doped Li-rich Li1.20Mn0.56Ni0.16Co0.08O2 as cathode with outstanding structural stability for Lithium-ion battery

The Li-rich Mn-based cathode materials exhibit great potential due to their ultrahigh specific capacity, but still suffer from low initial coulombic efficiency, inferior cycling stability, voltage decay and poor rate performance. In this study, we propose to enhance the structural stability and the electrochemical performances of Li1.20Mn0.56Ni0.16Co0.08O2 through the co-doping of Fe3+ and PO43-. The Fe3+ and PO43- are simultaneously doped in the precursor via a novel wet chemical method. In comparison with the undoped or mono-doped samples, the co-doped sample exhibits the best electrochemical performances owing to the synergistic effect of Fe3+ and PO43-, such as a high initial coulombic efficiency (88%), great cyclic stability (remains a specific capacity of 214 mAh g−1 after 130 cycles at 1 C) and mitigated voltage fade (2.12 mV per cycle). The synergistic mechanism of Fe3+ and PO43- is revealed based on X-ray diffraction, transmission electron microscope, scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical measurements. The co-doping of Fe3+ and PO43- constructs a stable oxygen-packed framework, which can alleviate lattice distortion, reduce the mixing of cations and increase the reversible reaction of 2 O2-/(O2)n-, contributing to outstanding structural stability. The synergetic strategy of anion and cation and the co-doping method in this work may provide some inspiration for designing the high-performance cathode materials of Lithium-ion battery.

Effect of Na Doping or Substitution on the Structural and Electrochemical Properties of Cobalt-Free Li-Rich Mn-Based Cathode Materials

Cobalt-free Li-rich Mn-based cathode materials are considered to be the next generation of Li-ion batteries due to low cost, high discharge capacities and high safety feature. However, there are still several serious issues that need to be solved urgently, such as low initial coulombic efficiency, low rate capability, poor cycling performance and voltage fading. Na doping or substitution is introduced to improve the electrochemical performance of Li1.2Mn0.6Ni0.2O2 cathode material, which is synthesized by sol-gel method. The effect of Na doping or substitution on the morphological, structural and electrochemical properties was systematically studied and analyzed by scanning electron microscope (SEM), X-Ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cell test system and electrochemical workstation. These results illustrate that lattice layer spacing is enlarged by Na doping or substitution, which is beneficial for the diffusion of Li-ion, and the voltage fading is successfully suppressed. The best electrochemical properties were obtained when Na doping, which is attributed to the stronger structural stability and better reversibility of Li+ during the initial charge and discharge process.

Influence of Calcination Temperature on the Electrochemical Performance of Li1.2[Ni0.13Co0.13Mn0.54]0.985Zr0.015O2 as Li-rich Cathode Material for Li-ion Batteries

Influence of Calcination Temperature on the Electrochemical Performance of Li1.2[Ni0.13Co0.13Mn0.54]0.985Zr0.015O2 as Li-rich Cathode Material for Li-ion Batteries

Enhanced electrochemical performance of Li1.2Mn0.54Ni0.13Co0.13O2 prepared by using activated carbon as template and carbon source

Enhanced electrochemical performance of Li1.2Mn0.54Ni0.13Co0.13O2 prepared by using activated carbon as template and carbon source

Synthesis and Performance Evaluation of SiO2 Coated Li-Rich Li1.2Ni0.13Mn0.54Co0.13O2 Cathode Materials for Li-Ion Batteries

Lithium rich layered oxides (LLO) are one of the potential candidates for Li-ion batteries. however, LLO materials have serious drawbacks such as poor cyclic stability, poor rate capability and rapid voltage decay upon cycling, which needs to be overcome in order to successfully commercialize them. In this work, SiO2 coating is employed (1.0%, 1.5%, and 2.0 wt. %) to combat these issues. Li1.2Ni0.13Mn0.54Co0.13O2 synthesis was carried out by sol-gel process and SiO2 coating was done using dry ball milling method. XRD analysis confirmed the synthesis of phase pure materials without the presence of any impurity phases. SEM and TEM analysis showed the synthesis of nanometric sized particles. Furthermore, TEM elemental mapping displayed the homogeneous distribution of SiO2 on the cathode particles. XPS was further employed to confirm the SiO2 on the cathode material. The electrochemical analysis showed that 1.0 wt.% SiO2 displayed the best performance in terms of rate capability. Uncoated Li1.2Ni0.13Mn0.54Co0.13O2 displayed a fast capacity fade, especially at higher C-rate. On the other hand, SiO2 coated Li1.2Ni0.13Mn0.54Co0.13O2 materials showed improved rate capability. Coated materials also showed improved cycling performance when compared with bare Li1.2Ni0.13Mn0.54Co0.13O2. The improved electrochemical performance can be attributed to the positive impact of SiO2 coating, which impedes the electrolyte oxidation by preventing the direct contact of cathode active material and electrolyte. Overall, the SiO2 coating had a positive impact on the electrochemical performance of Li1.2Ni0.13Mn0.54Co0.13O2 and can pave the way for commercialization of LLO materials.

Exploring the activating voltages on the electrochemical performances of Li1.17Ni0.139Co0.139Mn0.552O2 cathode materials

Lithium and manganese-rich oxide (LMR) is regarded as one of the next generation of the high energy density cathode materials. However, the activating voltages have a great impact on the electrochemical performances. Herein, we explore the effects of the activating voltages on the electrochemical performances of Li1.17Ni0.139Co0.139Mn0.552O2 cathode materials. The activating voltages can mainly affect the capacity release, rather than the cycling characteristics. The comparison study reveals that the layered structure can transform into spinel and/or nickel enriched structure due to the cation migration and the hardly-being reduced transition metals, especially for the Ni4+ during activation. Meanwhile, the surface side-reactions would also deteriorate the lithium kinetic characteristics, but the formed by-products coated on the cathode surface can resist the further attack from electrolyte, which favors to the following cycles. The Li1.17Ni0.139Co0.139Mn0.552O2 cathode materials activated to 4.6 V with 25 mA·g−1 can deliver capacities of 262.0 and 209.2 mAh·g−1 over 2.0–4.8/4.4 V at 1C (250 mA·g−1) and the highest energy densities. The appropriate activating voltages play critical roles in the optimization of the structure of LMR cathode materials and improving the electrochemical performances.

Enhanced electrochemical performance of F-doped Li1.2Mn4/6Ni1/6Co1/6O2.35 cathode materials for Li-ion batteries

F-doped cathode material Li1.2Mn4/6Ni1/6Co1/6O(2.35-x)Fx (x=0,0.05,0.10,0.15) were synthesized successfully by two-step co-precipitation method. X-ray diffraction pattern shows that fluorine doping does not bring impurities, but the lattice parameters increase slightly with fluorine content increasing in Li1.2Mn4/6Ni1/6Co1/6O(2.35-x)Fx. At the current density of 0.5C (125mAhg−1), Li1.2Mn4/6Ni1/6Co1/6O2.30F0.05 has the highest capacity retention (94.56%) and discharge capacity(177.4mA·h/g) after 50th cycles, while capacity retention and discharge capacity after 50th cycles of Li1.2Mn4/6Ni1/6Co1/6O2.35 material are only 86.19% and 164.7 mA·h/g. And Li1.2Mn4/6Ni1/6Co1/6O2.30F0.05 material exhibits a noticeable higher discharge capacity than other Li1.2Mn4/6Ni1/6Co1/6O(2.35-x)Fx (x=0, 0.10,0.15) materials at high current density. The initial discharge specific capacity of Li1.2Mn4/6Ni1/6Co1/6O2.30F0.05 material is increased to 121.1 mA·h/g and 82.3 mA·h/g compared to 91.1 mA·h/g and 66.8 mA·h/g of Li1.2Mn4/6Ni1/6Co1/6O2.35 material at 2C and 5C. It can be concluded that electrochemical performances of Li1.2Mn4/6Ni1/6Co1/6O2.35 material are improved due to fluorine doping.

Enhanced electrochemical performance of Li1.18Ni0.15Co0.15Mn0.52O2 cathode modified with aluminosilicate solid acid

Li-rich cathode material Li1.18Ni0.15Co0.15Mn0.52O2 is prepared by a sol–gel method and modified with aluminosilicate solid acid (Al2O3·SiO2) via an ultrasonic impregnation process. Compared with the pristine and Al2O3/SiO2-sole-modified counterparts, the Al2O3·SiO2 coating layer with high acid center strength on Li1.18Ni0.15Co0.15Mn0.52O2 material exhibits overall improved electrochemical performance. Galvanostatic charge–discharge tests at the current density of 200 mA g−1 displays the highest capacity retention of 72.5% and voltage retention of 95.1% after 200 cycles for Al2O3·SiO2-coated material. Meanwhile, a high rate capability of 99.2 mAh g−1 after 300 cycles is obtained with a good retention of 65.7% at the current density of 1 A g−1. The analysis of dQ/dV plots indicates the strong acid center strength of Al2O3·SiO2 coating layer on Li1.18Ni0.15Co0.15Mn0.52O2 cathode material can be favor of suppressing the voltage decay and reducing the side reactions between the electrode and the electrolyte.