Undoped LiNi0 Research Articles

Improving electrochemical performance of spinel-type Ni/Mn-based high-voltage cathode material for lithium-ion batteries via La-F co-doping combined with in-situ integrated perovskite LaMnO3 coating layer

Spinel-type LiNi0.5Mn1.5O4 (LNMO) can provide high-voltage and high theoretical specific capacity as cathode material for lithium-ion batteries (LIBs), thereby LNMO is particularly suitable for electric/hybrid electric vehicles that require high power. Unfortunately, both serious structural deformation derived from the Jahn-Teller effect of Mn3+ and decomposition of electrolyte during repetitive charge/discharge processes at high operating potential result in fast capacity fade. In this work, lanthanum and fluorine co-doping LiNi0.5La0.01Mn1.49O3.97F0.03 (LF-LNMO) is proposed to eliminate its inherent defects. Fluorine can suppress Jahn-Teller effect of Mn3+ by reducing the generation of Mn3+; La3+ ions in LF-LNMO play a role in solidly riveting atoms together in the structure, and LaMnO3 coating layer acts as a physical protection barrier suppressing adverse side reactions that may damage battery performance. Thanks to the synergistic effect derived from structural modification of F−, the pinning effect of La3+ ions, and LaMnO3 surface coating interface reconstruction, the LF-LNMO cathode provides the best cycling performance and rate performance among all investigated electrode materials. Such as, LF-LNMO cathode can provide 64.02% capacity retention after the 1000th cycle at 500 mA g−1 and 30 °C, which is much higher than that (25.56%) of the undoped LiNi0.5Mn1.5O4 (P-LNMO). Besides, LF-LNMO electrode also behaves the excellent high-temperature cycling performance. This work provides a new strategy enhancing structural stability of spinel-type Ni/Mn-based oxide and would motivate us to further devise and prepare high power cathode materials for LIBs.

A Single‐Pot Co‐Precipitation Synthesis Route for Ni‐Rich Layered Oxide Materials with High Cycling Stability

AbstractIn this work we report variations of LiNi0.88Mn0.06Co0.06O2 synthesised through a single‐pot oxalic acid co‐precipitation route, in which all cation precursors were added in the same step. The effects of Al‐doping, heat‐treatment temperature and Li precursor excess were investigated with physicochemical and electrochemical characterisation. Phase pure and well‐ordered polycrystalline materials were successfully synthesised for all Al‐doped and undoped compositions. Undoped LiNi0.88Mn0.06Co0.06O2 prepared at 750 °C with 4 at% excess Li precursor showed excellent cycling stability in NMC||LTO cells with an initial capacity of 201 mAh/g at 0.1 C at 20 °C, and a capacity retention of 81 % after 415 cycles. The Al‐doped variations LiNi0.88Mn0.04Co0.06Al0.02O2 and LiNi0.88Mn0.06Co0.04Al0.02O2 were synthesised, and they showed similar initial electrochemical performance to undoped LiNi0.88Mn0.06Co0.06O2, but Al‐doping via the oxalic acid co‐precipitation route resulted in shorter cycle life. The study outlines the importance of the processing parameters to achieve Ni‐rich layered oxides with a long cycle life without further surface modifications.

Stabilizing Effects on Structural and Thermal Properties of Al-Doped Ni-Rich Layered Oxides for Li Rechargeable Batteries

One of the key strategies to achieve high energy density for Li rechargeable batteries is through improved layered oxides cathode materials. Ni-rich layered oxides with Ni content above 80% have been under extensive attention as promising cathodes for next-generation Li-ion batteries due to the merits of high capacity, low cost, and low toxicity [1–3]. However, these materials still require further improvement to overcome inferior capacity retention and poor thermal stability originated from Ni-rich environments [1,4].We investigated Al-doped LiNi0.80Co0.15Mn0.05O2 and undoped LiNi0.80Co0.15Mn0.05O2 layered cathodes in view of the structural, electrochemical, and thermal properties. Synchrotron-based X-ray techniques were used to analyze their structural behavior systematically during electrochemical reactions and thermal decomposition. High resolution powder diffraction (HRPD) results show that Al-doping in Ni-rich NCM cathode alleviates anisotropic lattice distortion and structural collapse as well as preserves a wider LiO6 interslab thickness, even at highly deintercalated states comparing to the undoped cathode. Al-doped Ni-rich cathode exhibits lower polarization potential, better rate capability, and cyclability compared to undoped one. This can be attributed to the alleviation of anisotropic lattice changes and volume changes during cycling. More importantly, Al-doped Ni-rich cathode maintains a wider LiO6 interslab thickness without collapse at highly charged states, allowing Li-ions to be deintercalated/intercalated reversibly. This indicates that rigid structural integrity contributes to enhanced electrochemical performance. Moreover, in situ X-ray diffraction (XRD) during the heating process and differential scanning calorimetry (DSC) analysis demonstrate that Al-doped NCM cathode outperforms bare NCM cathode significantly in terms of thermal aspects. Specially, Al-doping improves thermal stability by delaying the onset temperatures of phase transformations during the heating process. These results demonstrate that Al-doping plays a major role in stabilizing the structure by suppressing abrupt lattice changes during cycling and the formation of a rock-salt phase during thermal decomposition reaction.Based on these experimental results, we will provide the structural evidence for the Al-doping effects on Ni-rich layered materials, thereby guiding for the strategical design factor in the development of layered cathodes with high performance. More detailed results and discussion will be presented in the PRiME 2020.

A Mg-Doped High-Nickel Layered Oxide Cathode Enabling Safer, High-Energy-Density Li-Ion Batteries

High-nickel layered oxide cathodes with a Ni content of >90% show substantial potential for next-generation lithium-ion batteries (LIBs) due to their high capacity and lower cost. However, they are plagued by rapid capacity decay and poor thermal stability, which hamper their practical viability. We present here Li0.98Mg0.02Ni0.94Co0.06O2 (NC-Mg) with 2% Mg doping, aiming to provide a strategic guideline for solving the issues. The Mg2+ ions occupy the lithium layer and are proposed to act as pillar ions, which substantially enhance the structural reversibility and reduce the anisotropic lattice distortion upon cycling, thereby greatly improving the electrochemical and thermal stability of NC-Mg compared to the undoped LiNi0.94Co0.06O2 (NC). Specifically, NC-Mg delivers 214 mA h g–1 with a capacity retention of 80.1% after 500 cycles in pouch-type full cells, much higher than the retention of NC (56.3%). A discharge capacity of 158 mA h g–1 at 10C rate demonstrates its remarkable rate capability. Addition...

Magnesium and silicon co-doped LiNi0.5Mn1.5O4 cathode material with outstanding cycling stability for lithium-ion batteries

The magnesium (Mg) and silicon (Si) co-doped LiNi0.5Mn1.5O4 sample has been obtained by sol-gel method. The effects of co-doping with magnesium and silicon ions on the phase structure, morphology and electrochemistry characteristics of LiNi0.5Mn1.5O4 are investigated by a series of physico-chemical characterizations. XRD results demonstrate that the magnesium and silicon ions successfully enter into the spinel structure and make the lattice parameter slightly increased. Moreover, the magnesium and silicon ions co-doped sample presents superior cycling stability. When cycled at 0.5 C, this sample still delivers 121 mAh g−1 after 100 cycles with outstanding retention of 98.86%, while the undoped LiNi0.5Mn1.5O4 sample only exhibits 104.5 mAh g−1 after 100 cycles with low retention of 79.17%. In addition, the Mg2+ and Si4+ co-doped sample shows outstanding rate capability and low charge transfer resistance.

Synthesis, electrochemical investigation and structural analysis of doped Li[Ni0.6Mn0.2Co0.2-xMx]O2 (x = 0, 0.05; M = Al, Fe, Sn) cathode materials

Layered Ni-rich Li[Ni0.6Mn0.2Co0.2-xMx]O2 cathode materials (x = 0, 0.05; M = Al, Fe, Sn) are synthesized via a co-precipitation synthesis route and the effect of dopants on the structure and electrochemical performance is investigated. All synthesized materials show a well-defined layered structure of the hexagonal α-NaFeO2 phase investigated by X-ray diffraction (XRD). Undoped LiNi0.6Mn0.2Co0.2O2 exhibits a discharge capacity of 170 mAh g−1 in Li-metal 2032 coin-type cells. Doped materials reach lower capacities between 145 mAh g−1 for Al and 160 mAh g−1 for Sn. However, all doped materials prolong the cycle life by up to 20%. Changes of the lattice parameter before and after delithiation yield information about structural stability. A smaller repulsion of the transition metal layer during delithiation in the Sn-doped material leads to a smaller expansion of the unit cell, which results in enhanced structural stability of the material. The improved structural stability of Sn-doped NMC cathode active material is proven by thermal investigations with the help of Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA).

Comparative Studies of Ti Doped LiNi0.7Co0.3O2 and LiNi0.7Co0.3O2 Nano Cathode Material for High Energy Density Li-Ion Battery

Ti doped LiNi0.7Co0.3O2 materials were investigated for their electrochemical characteristics. LiNi0.7Co0.3O2 and LiNi0.6Co0.3Ti0.1O2 materials were prepared using a self-propagating combustion method. The structure and morphology of the materials were characterized using X-Ray Diiffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-Ray Spectroscopy (EDX). The oxidation state of elements and their chemical environments were studied using X-Ray Photoelectron Spectroscopy (XPS). XRD results showed that the materials were all single phase with hexagonal layered structure of R-3m space group. The discharge capacities are between 135.5 and 151.1 mAhg-1. The LiNi0.7Co0.3O2 compound exhibits the highest first cycle capacity of 151.1 mAhg-1 over the voltage range of 2.5 to 4.2 V compared to the Ti doped sample LiNi0.6Co0.3Ti0.1O2, showing a capacity of 146 mAhg-1. However, at the 30th cycle, the Ti doped material shows the highest specific discharge capacity of 137.8 mAhg-1. The capacity fading is only about 5.6 % compared to 38.2% for undoped LiNi0.7Co0.3O2. Therefore, eventhough the undoped LiNi0.7Co0.3O2 material has a higher first cycle capacity, the doped compounds exhibits much better capacity retention over 30 cycles

Specific Capacity and Capacity Fading of Interstitial and Substitutional Doping of Li in LiNi0.6Co0.3Ti0.1O2 Nano Cathode Material for High Energy Density Li-Ion Battery

Pure and single phase LiNi0.6Co0.3Ti0.1O2, Li1.05Ni0.6Co0.3Ti0.1O2, Li1.05Ni0.55Co0.3Ti0.1O2 materials were successfully prepared using a self-propagating combustion method. The structure and morphology of the materials were characterized using X-Ray Diiffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-Ray Spectroscopy (EDX). The oxidation state of elements and their chemical environments were studied using X-Ray Photoelectron Spectroscopy (XPS). The electrochemical performances of the materials were carried by means of galvanostatic charge-discharge on the fabricated cells. XRD results showed that the materials are impurity-free and single phase with well ordered hexagonal layered structure of R-3m space group. The discharge capacities are between 141 and 145 mAhg-1. The interstitially doped Li1.05Ni0.6Co0.3Ti0.1O2 compound exhibits the highest first cycle capacity of 145.3 mAhg-1 over the voltage range of 2.5 to 4.2 V compared to the undoped sample, LiNi0.6Co0.3Ti0.1O2, showing a capacity of 105.5 mAhg-1. The 70th cycle revealed that the Li interstitially doped material (Li1.05Ni0.6Co0.3Ti0.1O2) shows the highest specific discharge capacity of 132.4 mAhg-1. The capacity fading is only about 8.9% compared to 25.4% for undoped LiNi0.6Co0.3Ti0.1O2 and 10.4% for Li substitutionally doped material (Li1.05Ni0.55Co0.3Ti0.1O2). XPS studies showed that the binding energy of Li 1s is lowest for the best performance compound meaning that the Li+ ions can be extracted more easily from Li1.05Ni0.6Co0.3Ti0.1O2 than the other two materials supporting the electrochemical behaviour of the materials.

Synthesis and electrochemical performance of Sn-doped LiNi0.5Mn1.5O4 cathode material for high-voltage lithium-ion batteries

LiNi0.5Mn1.5− x Sn x O4 (0 ≤ x ≤ 0.1) cathode materials with uniform and fine particle sizes were successfully synthesized by a two-step calcination of solid-state reaction method. As the cathode materials for lithium ion batteries, the LiNi0.5Mn1.48Sn0.02O4 shows the highest specific capacity and cycle stability. In the potential range of 3.5–4.9 V at room temperature, LiNi0.5Mn1.48Sn0.02O4 composite material shows a discharge capacity of more than 117 mA h g−1 at 0.1 C, while the corresponding discharge capacity of undoped LiNi0.5Mn1.5O4 is only 101 mA h g−1. Moreover, in cycle performance, all the LiNi0.5Mn1.5− x Sn x O4 (0 ≤ x ≤ 0.1) samples show better capacity retention than the undoped LiNi0.5Mn1.5O4 at 1 C rate after 100 cycles. Especially, for the LiNi0.5Mn1.5O4, the discharge capacity after 100 cycles is 90 mA h g−1, while the corresponding discharge capacities of the undoped LiNi0.5Mn1.5O4 is only 56.1 mA h g−1. The significantly enhanced D Li+ and the enlarged electronic conductivity make the Sn-doped spinel LiNi0.5Mn1.5O4 material present even more excellent electrochemical performances. These results reveal that Sn-doping is an effective way to improve electrochemical performances of LiNi0.5Mn1.5O4.

Improving the electrochemical properties of high-energy cathode material LiNi0.5Co0.2Mn0.3O2 by Zr doping and sintering in oxygen

The powders of layered structured LiNi0.5Co0.2Mn0.3O2 cathode material are synthesized by a thermal polymerization method in the temperatures range from 750°C to 950°C in air and oxygen. It is found that the LiNi0.5Co0.2Mn0.3O2 powder sintered in oxygen has significantly decreased degree of cationic mixing. The discharge capacities of the samples sintered in oxygen are higher than those of the samples sintered in air. The sample sintered at 900°C in oxygen has the highest ratio of I003/I104 and the highest initial discharge capacities of 200mAh g−1 at a rate of 0.1C in the voltage range of 2.8–4.5V. In order to improve the cycling stability of the LiNi0.5Co0.2Mn0.3O2 electrode, a series of Zr-doped LiNi0.5Co0.2Mn0.3O2 electrodes (LiNi0.5Co0.2Mn0.3−xZrxO2, x=0.01, 0.02, 0.03, 0.04, 0.05) are also prepared. The LiNi0.5Co0.2Mn0.3−xZrxO2 electrodes show much enhanced cycling performance compared to the un-doped LiNi0.5Co0.2Mn0.3O2 electrode. The LiNi0.5Co0.2Mn0.29Zr0.01O2 electrode exhibits the best electrochemical performance with the capacity retention of 93.92% after 100cycles at 0.2C in the voltage range of 2.8–4.5V, while the un-doped LiNi0.5Co0.2Mn0.3O2 electrode exhibits capacity retention of only 83.33% after 100cycles. The LiNi0.5Co0.2Mn0.29Zr0.01O2 electrode also shows obvious improved rate capability relative to that of the un-doped electrode.

Specific Capacity and Capacity Fading of Interstitial and Substitutional Doping of Li in LiNi0.3Co0.3Mn0.3Ti0.1O2 cathode Material for High Energy Density Li-Ion

Pure and single phase LiNi0.3Co0.3Mn0.3Ti0.1O2 , Li1.05Ni0.3Co0.3Mn0.3Ti0.1O2 and Li1.05Ni0.3Co0. 25Mn0.3Ti0.1O2 materials were successfully prepared using a self-propagating combustion method. The structure and morphology of the materials were characterized using X-Ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and the elemental analysis were done using by Energy Dispersive X-Ray Spectroscopy (EDX). The oxidation state of element and their chemical environments were identified using X-Ray photoelectron Spectroscopy (XPS). The electrochemical performances of the materials were carried by means of galvanostatic charge-discharge test on the fabricated cells. XRD results showed that the materials are impurity-free and single phase with well ordered hexagonal layered structure of R-3m space group. The different samples annealed at 700 °C for 48h showed variations in discharge capacities. The discharge capacities are between 130 and 141 mAhg-1. The undoped LiNi0.3Co0.3Mn0.3Ti0.1O2 compound exhibits the highest first cycle capacity of 141.3 mAhg-1 over the voltage range of 2.5 to 4.2 V and the lowest capacity was 130.43 mAhg-1 for sample Li1.05Ni0.3Co0. 25Mn0.3Ti0.1O2. The 30th cycle revealed that the Li interstitially doped material is (Li1.05Ni0.3Co0.3Mn0.3Ti0.1O2) shows the highest specific discharge capacity of 131.74 mAhg-1. The capacity fading is only about 1.3% compared to 7.66% for undoped LiNi0.3Co0.3Mn0.3Ti0.1O2 and 12.3% for Li substitutionally doped material (Li1.05Ni0.3Co0. 25Mn0.3Ti0.1O2). The XPS studies showed that the binding energy of Li 1s is lowest for the best performance compound meaning that the Li+ ions can be extracted more easily from Li1.05Ni0.3Co0.3Mn0.3Ti0.1O2 than the other two materials. Therefore, XPS results show that the deintercalation of Li from the interstitially doped compound was much more efficient and enhanced the electrochemical performance of the material. The results also suggest that the self-propagating combustion method is a good synthesis method for the preparation of LiMn0.3Co0.3Ni0.3Ti0.1O2 and their Li doped materials for applications in lithium-ion batteries.

Preparation of spinel LiNi0.5Mn1.5O4 and Cr-doped LiNi0.5Mn1.5O4 cathode materials by tartaric acid assisted sol–gel method

In this article, LiNi0.5Mn1.5O4 and LiNi0.4Cr0.15Mn1.45O4 are prepared by the tartaric acid-assisted sol–gel method. It can be found that Cr doping not only can suppress the formation of impurity phase in the final product but also can increase the cation ordering in the spinel structure. Morphology observation reveals that the introduction of tartaric acid in the preparation leads to a controlled cubic morphology and a narrow particle size distribution. It is clear that both LiNi0.5Mn1.5O4 and LiNi0.4Cr0.15Mn1.45O4 consist of octahedrons with the particle size ranging from 0.5 to 1.5μm. Charge/discharge tests show that LiNi0.4Cr0.15Mn1.45O4 can deliver a higher initial discharge capacity (143.9mAhg−1) than that of undoped LiNi0.5Mn1.5O4 (136.6mAhg−1). After 40 cycles, the reversible discharge capacity of LiNi0.4Cr0.15Mn1.45O4 can be still maintained at 139.7mAhg−1. For comparison, LiNi0.5Mn1.5O4 only shows a reversible discharge capacity of 127.7mAhg−1. It suggests that Cr substitution for Ni and Mn in the spinel structure can effectively improve the electrochemical performance of LiNi0.5Mn1.5O4.

Na-doped Ni-rich LiNi0.5Co0.2Mn0.3O2 cathode material with both high rate capability and high tap density for lithium ion batteries.

Na-doped Ni-rich LiNi0.5Co0.2Mn0.3O2 cathode material, Li0.97Na0.03Ni0.5Co0.2Mn0.3O2, is synthesized by a hydroxide co-precipitation route. The structural characterization reveals that the substitution of Na for Li results in a more ordered α-NaFeO2 structure, enlarges Li layer spacing, and reduces the degree of cation mixing. The Li0.97Na0.03Ni0.5Co0.2Mn0.3O2 material has a high tap density of 2.17 g cm(-3) that meets the commercial requirement in lithium ion batteries (LIBs). The galvanostatic charge/discharge results show that the electrochemical performance of the Li0.97Na0.03Ni0.5Co0.2Mn0.3O2 is significantly improved. At 0.2, 1, 10, 30 and 50 C, the specific capacities of the Li0.97Na0.03Ni0.5Co0.2Mn0.3O2 are 228.43, 163.12, 121.43, 95.56 and 60.09 mA h g(-1), respectively, which are superior to those of the undoped LiNi0.5Co0.2Mn0.3O2 due to the enlargement of Li layer spacing, the decreased degree of cation mixing, and the rapid diffusion of Li-ion in the bulk lattice after the substitution of Na for Li. Therefore, the Na-doped Ni-rich LiNi0.5Co0.2Mn0.3O2 material is a promising cathode candidate for the next generation of LIBs.

Facile synthesis of aluminum-doped LiNi0.5Mn1.5O4 hollow microspheres and their electrochemical performance for high-voltage Li-ion batteries

This paper presents the preparation of LiNi0.5Mn1.5O4 and aluminum (Al) doped LiNi0.5Mn1.5O4 hollow microspheres as 5V cathodes using monodisperse MnCO3 microspheres as precursor and template, which were synthesized using MnSO4·H2O, NaHCO3 and ethanol in water at room temperature. XRD and morphology characterization results indicated that the as-prepared LiNi0.5Mn1.5O4 and Al doped LiNi0.5Mn1.5O4 were both spinel structure, and have particle sizes of 2–3μm. The cathode electrochemical properties of LiNi0.5Mn1.5O4 and Al doped LiNi0.5Mn1.5O4 hollow microspheres (as 5V cathodes) were evaluated and compared by galvanostatic cycling (GC) vs. Li/Li+ at the current rate 1C in 2.7–4.8V. The specific initial capacities of all samples were in the range of 70–120mAhg−1. Compared to undoped LiNi0.5Mn1.5O4, Al doped LiNi0.5Mn1.5O4 hollow structures can effectively improve discharge capacity (up to 140 (±5)mAhg−1) and cycling stability (70% capacity retention after 200 cycles) as high voltage cathode materials.

Preparation and Electrochemical Performance of Mg-Doped LiNi<sub>0.4</sub>Co<sub>0.2</sub>Mn<sub>0.4</sub>O<sub>2</sub> Cathode Materials by Urea Co-Precipitation

The Mg-doped LiNi0.4Co0.2-xMn0.4MgxO2 cathode materials (x=0, 0.01, 0.02 and 0.03) were synthesized by a urea co-precipitation method. Its structure and electrochemical properties were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and electrochemical performance tests. XRD studies indicate that the Mg-doped LiNi0.4Co0.2Mn0.4O2 samples perform the same layered structure as the undoped LiNi0.4Co0.2Mn0.4O2. SEM images show that the particle size of Mg-doped LiNi0.4Co0.2Mn0.4O2 is smaller than the undoped LiNi0.4Co0.2Mn0.4O2 sample. Charge-discharge tests confirm that the rate capacity and cycling performance of LiNi0.4Co0.2-xMn0.4MgxO2 are improved by Mg-doped. The optimal doping content of Mg is x=0.02 in the LiNi0.4Co0.2-xMn0.4MgxO2 samples, which can achieve high initial charge-discharge capacity and good cyclic stability. The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through the Mg-doping. The improved electrochemical performances of the Mg-doped LiNi0.4Co0.2Mn0.4O2 cathode materials are attributed to the addition of Mg2+ ion by stabilizing the layered structure.

Electrochemical investigations of the LiNi0.45M0.10Mn1.45O4 (M = Fe, Co, Cr) 5 V cathode materials for lithium ion batteries

LiNi0.5Mn1.5O4 and LiNi0.45M0.10Mn1.45O4 (M=Fe, Co, Cr) powders are prepared and systematically investigated as 5V cathode materials for lithium-ion batteries. X-ray diffraction, Raman spectroscopy and scanning electron microscopy are employed to study their structures. The electrochemical cyclic performance and rate capability at room temperature and 55°C are characterized and compared. The results indicate that the introductions of Fe, Co or Cr ions favor the crystal structure of the spinel in a Fd3¯m symmetry compared with a symmetry of P4332 for the un-doped LiNi0.5Mn1.5O4. Excellent cycle life is measured for these 5V Co- and Fe-doped electrodes. When cycled at 1C rate, about 95.9%, 93.1% and 81.7% of their initial capacities can be retained after 500 cycles for LiNi0.45Co0.10Mn1.45O4, LiNi0.45Fe0.10Mn1.45O4 and LiNi0.45Cr0.10Mn1.45O4, respectively. Their electrochemical performances at 55°C are also much better than the un-doped sample. Three possible capacity fading mechanisms including structural transformation, the dissolution of the spinel into the electrolyte, and the oxidation of the electrolyte are discussed. The decomposition of the electrolyte is regarded as the most important mechanism.

Synthesis and electrochemical properties of Mg-doped LiNi0.6Co0.2Mn0.2O2 cathode materials for Li-ion battery

The layered LiNi0.6Co0.2−x Mn0.2Mg x O2 (x=0.00, 0.03, 0.05, 0.07) cathode materials were prepared by a co-precipitation method. The properties of the Mg-doped LiNi0.6Co0.2Mn0.2O2 were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements. XRD studies showed that the Mg-doped LiNi0.6Co0.2Mn0.2O2 had the same layered structure as the undoped LiNi0.6Co0.2Mn0.2O2. The SEM images exhibited that the particle size of Mg-doped LiNi0.6Co0.2Mn0.2O2 was finer than that of the undoped LiNi0.6Co0.2 Mn0.2O2 and that the smallest particle size is only about 1 μm. The Mg-doped LiNi0.6Co0.2Mn0.2O2 samples were investigated on the Li extraction/insertion performances through charge/discharge, cyclic voltammogram (CV), and electrochemical impedance spectra(EIS). The optimal doping content of Mg was that x= 0.03 in the LiNi0.6Co0.2−x Mn0.2Mg x O2 samples to achieve high discharge capacity and good cyclic stability. The electrode reaction reversibility and electronic conductivity was enhanced, and the charge transfer resistance was decreased through Mg-doping. The improved electrochemical performances of the Mg-doped LiNi0.6Co0.2Mn0.2O2 cathode materials are attributed to the addition of Mg2+ ion by stabilizing the layer structure.

Improved electrochemical properties of Sr2+-doped LiNi0.8Co0.2O2 synthesized via a sol-gel route using tartaric acid as a chelating agent

Single-phase undoped LiNi0.8Co0.2O2 and Sr2+-doped LiNi0.8Co0.2O2 were synthesized by a low temperature tartaric acid assisted sol-gel method. Small quantities of Sr2+ were used as dopants in order to improve the electrochemical characteristics, especially the capacity and cycling performance of LiNi0.8Co0.2O2. The electrochemical performance of the undoped material was promising with a first discharge capacity of 174 mAh/g and 165 mAh/g after 10 cycles with a 100% cycling efficiency in the tenth cycle. Addition of Sr2+ for Li in minimum quantities with the Sr2+/Li+ dopant mole ratio ranging from 10−4 to 10−8 resulted in improved electrochemical properties for dopant mole ratio of 10−6. The first discharge capacity was 182 mAh/g and the tenth was 174 mAh/g at the 10th discharge. The synthesis of Sr2+-doped LiNi0.8Co0.2O2 and its improved electrochemical properties have been discussed for the first time. The improved electrochemical properties of Sr2+-doped LiNi0.8Co0.2O2 system are explained based on defect models.