Li-rich Layered Oxide Cathode Materials Research Articles

Dependences of Discharge Capacity, Retention of Discharge Capacity, Average Discharge Voltage and Energy Density, and Rate Capability on the Composition of XLi2MnO3-YLiNi1/2Mn1/2O2-(1-x-y)LiNi1/3Co1/3Mn1/3O2 Li-Rich Solid-Solution Cathode Materials for Li-Ion Battery (II)

A great deal attention has recently been focused on the Li-rich solid-solution layered oxide cathode material Li2MnO3-LiMO2 (LLO, M = Co, Ni, etc.), which exhibits a discharge capacity of more than 200 mAhg-1 when operated above 4.6 V for lithium ion battery. In this study, in order to find the optimal composition of the LLO exhibiting high cathode performance, which are composed of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 (or LiCoO2, LiNiO2) and LiNi0.5Mn0.5O2, the selected 120 samples having different composition were synthesized under identical preparation conditions and the dependence of the performance of the cathode material on the percentages of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 (or LiCoO2, LiNiO2) and LiNi0.5Mn0.5O2 in the LLO samples was examined under same experimental conditions in the viewpoint of discharge capacity, retention of discharge capacity, average discharge voltage, energy density and rate capability. In each viewpoint, using ternary phase diagrams, the dependence of each property on the percentages of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 and LiNi0.5Mn0.5O2 in the LLO samples was evaluated. Based on the results obtained, it was comprehensively concluded that Li[Ni0.208Li0.183Co0.033Mn0.575]O2 (55% Li2MnO3-35% LiNi1/2Mn1/2O2-10% LiNi1/3Co1/3Mn1/3O2) possesses the best composition as cathode material for LIBs among the testes 120 samples. In addition, the synthesis condition of Li[Ni0.208Li0.183Co0.033Mn0.575]O2 was examined more in the viewpoint of annealing temperature.

Engineering hetero-epitaxial nanostructures with aligned Li-ion channels in Li-rich layered oxides for high-performance cathode application

As a promising cathode material for Li-ion batteries (LIBs), Li-rich layered oxide (LLO) has attracted the most interest due to its superior performance and attractive characteristics, such as, extremely high capacity and energy density, low cost, and environmental friendliness. However, LLO cathode materials are facing a fundamental challenge of performance degradation as a result of the intrinsically poor rate capability and structural instability. Here we report the synthesis of high performance spinel/LLO heterostructured composite with aligned Li-ion channels by a composition modulated epitaxy method. The hetero-epitaxial nanostructure provides highly anisotropic Li-ion diffusion channels in spinel/LLO composite that significantly improve the electrochemical performance. Discharge capacities as high as 307, 282, 269, 227, 200mAhg−1 at 0.1, 0.5, 1.0, 3.0 and 5.0C rates, respectively, and reversible capacity of 286mAhg−1 after 100 cycles at 0.2C rate can be attained. This work sheds light on the comprehensive design of heterostructured composites for high-performance electrode applications and opens up new opportunities for next-generation LIBs.

Nanoscale characterization of charged/discharged lithium-rich thin film cathode by scanning probe microscopy techniques

Abstract Lithium ion intercalation and de-intercalation at electrodes are critically issues for development of the high performance Li-ion batteries. However, the changes of the surface morphologies, electrical and mechanical properties during the charge/discharge cycles are still not well understood. In this study, by using Atomic Force Microscopy (AFM), Electrochemical Strain Microscopy (ESM), AM-FM (Amplitude Modulation - Frequency Modulation), and conductive AFM (c-AFM) techniques, we have studied the significant changes, with nanoscale resolution, on the surface topography, electrochemical deformation, stiffness/elastic modulus, and electronic conductivity of Li-rich layered oxide cathode under the first cycle of galvonostatic charging/discharging process. This study has established the relationship between the nanoscale morphology and properties variations and the macroscopic charge/discharge processes for the Li-rich layered oxide cathode material, and the results also prove the feasibility of combining various Scanning Probe Microscopy (SPM) based techniques on the studies of lithium ion battery materials.

Tailoring Anisotropic Li-Ion Transport Tunnels on Orthogonally Arranged Li-Rich Layered Oxide Nanoplates Toward High-Performance Li-Ion Batteries.

High-performance Li-rich layered oxide (LRLO) cathode material is appealing for next-generation Li-ion batteries owing to its high specific capacity (>300 mAh g-1). Despite intense studies in the past decade, the low initial Coulombic efficiency and unsatisfactory cycling stability of LRLO still remain as great challenges for its practical applications. Here, we report a rational design of the orthogonally arranged {010}-oriented LRLO nanoplates with built-in anisotropic Li+ ion transport tunnels. Such a novel structure enables fast Li+ ion intercalation and deintercalation kinetics and enhances structural stability of LRLO. Theoretical calculations and experimental characterizations demonstrate the successful synthesis of target cathode material that delivers an initial discharge capacity as high as 303 mAh g-1 with an initial Coulombic efficiency of 93%. After 200 cycles at 1.0 C rate, an excellent capacity retention of 92% can be attained. Our method reported here opens a door to the development of high-performance Ni-Co-Mn-based cathode materials for high-energy density Li-ion batteries.

Dependences of Discharge Capacity, Retention of Discharge Capacity, Average Discharge Voltage and Energy Density, and Rate Capability on the Composition of xLi2MnO3-yLiNi1/2Mn1/2O2-(1-x-y)LiNi1/3Co1/3Mn1/3O2 Li-rich Solid-Solution Cathode Materials for Li-Ion Battery

A great deal attention has recently been focused on the Li-rich solid-solution layered oxide cathode material Li2MnO3-LiMO2 (LLO, M = Co, Ni, etc.), which exhibits a discharge capacity of more than 200 mAhg-1 when operated above 4.6 V for lithium ion battery. In this study, in order to find the optimal composition of the LLO exhibiting high cathode performance, which are composed of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 and LiNi0.5Mn0.5O2, the selected 75 samples having different composition were synthesized under identical preparation conditions and the dependence of the performance of the cathode material on the percentages of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 and LiNi0.5Mn0.5O2 in the LLO samples was examined under same experimental conditions in the viewpoint of discharge capacity, retention of discharge capacity, average discharge voltage, energy density and rate capability. In each viewpoint, using ternary phase diagrams, the dependence of each property on the percentages of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 and LiNi0.5Mn0.5O2 in the LLO samples was evaluated. Based on the results obtained, it was comprehensively concluded that Li[Ni0.208Li0.183Co0.033Mn0.575]O2 (55% Li2MnO3-35% LiNi1/2Mn1/2O2-10% LiNi1/3Co1/3Mn1/3O2) possesses the best composition as cathode material for LIBs.

Improving rate capability and decelerating voltage decay of Li-rich layered oxide cathodes via selenium doping to stabilize oxygen

Abstract To improve the rate performance and decelerate the voltage decay of Li-rich layered oxide cathode materials, a series of cathode materials Li1.2[Mn0.7Ni0.2Co0.1]0.8−xSexO2 (x = 0, 0.07, 0.14 and 0.21) was synthesized via co-precipitation. Based on the characterization results, it can be concluded that uniform Se6+ doping can improve the degree of crystallinity of Li2MnO3, resulting in a better ordering of atoms in the transition metal layer of this type of cathode materials. In the electrochemical experiments, compared to un-doped samples, one of the Se doped samples (LLMO-Se0.14) exhibited a longer sloping region and shorter potential plateau in the initial charge curves, a larger first coulombic efficiency (ca. 77%), better rate capability (178 mAhm g−1 at 10 C) and higher mid-point voltage (MPV) retention (ca. 95%) after 100 cycles. These results prove that Se doping can effectively improve the rate capability and decelerate the voltage decay process of these cathode materials during cycling via suppressing the oxidation process of O2− to O2 and curbing a layered-to-spinel phase transformation. The above-mentioned functions of Se doping are probably due to the higher bonding energy of Se O than that of Mn O.

Investigation of Interfacial Phenomena of High-Voltage Li-Ion Battery with Li-Rich Layered Oxide Cathode

Enabling the high energy density Li-ion batteries requires the use of high-capacity cathode material such as Li-rich layered oxide cathode (xLi2MnO3·(1-x)LiMO2 (M=Mn,Ni,Co)) that can be charged to high-voltage above 4.5 V vs. Li/Li+. A critical limiting factor for high-voltage battery operation is however the anodic and thermal instability of conventional electrolyte, which causes rapid performance fade and safety issue, in particular, at elevated temperatures. Our recent research results have shown that the use of functional additives enables the cell operation in such harsh conditions. Spectroscopic surface analysis data indicated that structural degradation of both Li-rich layered oxide cathode and graphite anode materials and instability of surface film at cathode during cycling in the conventional electrolyte were the main reasons for the rise of interfacial resistance and performance fade. Nonetheless, those problems can be resolved through interfacial stabilization using appropriate electrolyte additives. In this presentation, we report the interfacial phenomena and high-energy performance of Li-rich layered oxide cathode under a harsh condition of high charge cut-off voltage above 4.6 V vs. Li/Li+. The mechanistic studies of surface film/solid electrolyte interphase (SEI) layer formation and composition of cathode and anode using ex situ ATR FTIR spectroscopy combined with X-ray photoelectron spectroscopy and scanning electron microscopy, and structural changes using Raman spectroscopy, and the correlation between interfacial phenomena and high-voltage cycling performance would be discussed.

Understanding the interfacial phenomena of a 4.7 V and 55 °C Li-ion battery with Li-rich layered oxide cathode and graphite anode and its correlation to high-energy cycling performance

Research progress of high-energy performance and interfacial phenomena of Li1.13Mn0.463Ni0.203Co0.203O2 cathode and graphite anode in a 55 °C full-cell under an aggressive charge cut-off voltage to 4.7 V (4.75 V vs. Li/Li+) is reported. Although anodic instability of conventional electrolyte is the critical issue on high-voltage and high-temperature cell operation, interfacial phenomena and the solution to performance improvement have not been reported. Surface spectroscopic evidence revealed that structural degradation of both cathode and anode materials, instability of surface film at cathode, and metal-dissolution from cathode and -deposition at anode, and a rise of interfacial resistance with high-voltage cycling in 55 °C conventional electrolyte are resolved by the formation of a stable surface film with organic/inorganic mixtures at cathode and solid electrolyte interphase (SEI) at anode using blended additives of fluorinated linear carbonate and vinylene carbonate. As a result, significantly improved cycling stability of 77% capacity retention delivering 227−174 mAhg−1 after 50 cycles is obtained, corresponding to 819−609 Wh per kg of cathode active material. Interfacial stabilization approach would pave the way of controlling the performance and safety, and widening the practical application of Li-rich layered oxide cathode materials and high-voltage electrolyte materials in various high-energy density Li-ion batteries.

Effect of calcination temperature on microstructure and electrochemical performance of lithium-rich layered oxide cathode materials

Lithium-rich layered oxide cathode materials (Li1.2Mn0.56Ni0.16Co0.08O2 (LLMO)) were synthesized via a two-step synthesis method involving co-precipitation and high-temperature calcination. The effects of calcination temperature on the cathode materials were studied in detail. Structural and morphological characterizations revealed that a well-crystallized layered structure was obtained at a higher calcination temperature. Electrochemical performance evaluation revealed that a cathode material obtained at a calcination temperature of 850°C delivered a high initial discharge capacity of 266.8mAhg−1 at a 0.1C rate and a capacity retention rate of 95.8% after 100 cycles as well as excellent rate capability. Another sample calcinated at 900°C exhibited good cycling stability. It is concluded that the structural stability and electrochemical performance of Li-rich layered oxide cathode materials were strongly dependent on calcination temperatures. The results suggest that a calcination temperature in a range of 850–900°C could promote electrochemical performance of this type of cathode materials.

Enhanced electrochemical performance and thermal stability of a CePO4-coated Li1.2Ni0.13Co0.13Mn0.54O2 cathode material for lithium-ion batteries

CePO4 coating via a simple precipitation method enhances the thermal stability of the layered Li1.2Ni0.13Co0.13Mn0.54O2 cathode material.

Mitigation of Layered to Spinel Conversion of a Li-Rich Layered Metal Oxide Cathode Material for Li-Ion Batteries

We have prepared the Li-rich layered NMC composite cathode material of the composition 0.3Li2MnO30.7LiMn0.33Ni0.33Co0.33O2, (NMC) with 5 wt% Na doping. The latter material with composition of 0.3Li2MnO3.0.7Li0.97Na0.03Mn0.33Ni0.33Co0.33O2, synthesized as 200–300 nm size particles, was compared to its counterpart without Na. The discharge rate capability of the Li-rich NMC was greatly improved at both room temperature and 50°C with the Na doping. The Na doped material exhibited significantly higher conductivity than its un-doped analog as evidenced by dc electronic conductivity data and impedance of Li cells. Charge/discharge cycling results of Li cells at 50°C indicated that the voltage decay of Li-rich NMC accompanied by a layer to spinel structural conversion was mitigated with Na doping. XRD analysis revealed that ionic exchange of Na occurs upon contact of the cathode material with the electrolyte and produces a volume expansion of the crystal lattice which triggers a favorable metal (probably Ni) migration to Li depleted regions during oxidation of Li2MnO3 in the first cycle. XANES data showed that Na doped NMC has better Ni reduction efficiency to provide higher rate capability. EXAFS data supported this conclusion by showing that in the case of Na doped NMC, the structure has larger crystal cage allowing for better metal migration into the Li depleted regions located in the layered unit cell of C2/m space group. XANES of Mn K-edge supported by pre-edge analysis also revealed that during charging of the electrode, the Na doped NMC was oxidized to a higher Mn valence state compared to its undoped counterpart.