Concentration-gradient Material Research Articles

Highly stable nickel-rich cathode materials LiNi0.90Co0.05Mn0.05O2 with Mn concentration gradient for lithium-ion batteries

Ni-rich layered cathode materials (LiNixCoyMn1-x-yO2) have attracted much attention due to their high energy density and environmentally friendly advantages. However, the capacity fading and structural instability with the increase of Ni content are still the main problems restricting the commercialization of high nickel cathodes. In this paper, the method of co-precipitation and calcination is used to prepare LiNi0.90Co0.05Mn0.05O2 (CG-NCM5) with Mn concentration gradient, which the Ni content is decreasing from the core to the outer of CG-NCM5, while the Mn content is increasing. The CG-NCM5 has less Li/Ni mixing and a good layered structure. More importantly, the Mn-rich outer plays a key role in preventing the appearance of microcracks and enhancing the structure stability, because it can effectively suppress the volume change stemming from the phase transition during charge/discharge process. Meanwhile, the low Ni on the surface reduces the highly reactive Ni4+ that easily reacts with electrolyte, mitigates material surface degradation and accelerates lithium-ion transport. Therefore, it exhibits a superior reversible capacity of 191.4 mAh/gat 1C and a capacity retention of 83.7 % after 200 cycles in 2.7–4.3 V. These results indicate that Mn concentration gradient materials may provide a practical approach to highly stable nickel-rich cathode materials for lithium-ion batteries.

Synergistic modification of Ni-rich full concentration gradient materials with enhanced thermal stability

Major challenge hindering the large-scale applications of Ni-rich cathode materials (CAMs) lies on the poor cycle (especially under elevated temperature or high cutoff voltage) and thermal stability due to the highly reactive Ni4+. Herein, the full concentration strategy is combined with Ti pillar and Li2ZrO3 (LZO) coating modification, on which a high-performance CAM with elevated kinetics and stability, CGTZ-1, is obtained. It proves that both cycle and thermal stability can be greatly enhanced by the concentration gradient design and the LZO coating. Whereas the promoted Li+ diffusion coefficient is largely attributed to the Ti pillar. The optimal resultant CAM shows high capacity retention of 88.1% after 200 cycles under 55°C, while that of pristine is only 32.1%. More importantly, it also shows a high thermal release temperature of 261.5°C (vs 222.3°C of the pristine), which demonstrates the effectiveness of this synergistic modification strategy.

Cobalt-free concentration-gradient Li[Ni0.9Mn0.1]O2 cathode material for lithium-ion batteries

The cathodes of LiNiO2 (LNO), Li[Ni0.9Mn0.1]O2 (LNM91) and the concentration gradient material Li[Ni0.9Mn0.1]O2 (G-LNM91) were synthesized by co-precipitation method, and SEM, XRD, TEM and electrochemical tests were performed. SEM images show that the primary needle-like particles on spherical surface of the gradient G-LNM91 are the densest. The results of EDX linear scan show that for gradient precursor G-NM91, the relative atomic content of Ni element gradually decreases from 98.21% at the center of the particle to 80.66% at the cross surface of the particle (the content of Mn from 1.79% gradually increases to 19.34%). For the final product G-LNM91, the relative atomic content of Ni element in the center decreases to 94.07%, and at the edge increases to 85.17%. XRD tests indicate that the samples doped with Mn have good layered structure. TEM images show that the lattice fringes of the samples doped with Mn are more obvious. The results of Electrochemical performance tests show that manganese substitution has a significant effect on improving the cycle performance of LiNiO2, and G-LNM91 has the best cycle performance. Under a voltage range of 2.75–4.3 V, the initial discharge capacity of G-LNM91 cathode material at 0.1 C is 200 mA h/g. After 200 cycles at 1 C, the capacity retention rate remains around 87.5%. The initial discharge capacity of LNM91 is 180 mA h/g and the retention rate is 78.5%; the capacity retention rate of LiNiO2 is only 55.2%, even though the initial specific discharge capacity is 207 mA h/g.

Hierarchical nickel valence gradient stabilizes high-nickel content layered cathode materials

High-nickel content cathode materials offer high energy density. However, the structural and surface instability may cause poor capacity retention and thermal stability of them. To circumvent this problem, nickel concentration-gradient materials have been developed to enhance high-nickel content cathode materials’ thermal and cycling stability. Even though promising, the fundamental mechanism of the nickel concentration gradient’s stabilization effect remains elusive because it is inseparable from nickel’s valence gradient effect. To isolate nickel’s valence gradient effect and understand its fundamental stabilization mechanism, we design and synthesize a LiNi0.8Mn0.1Co0.1O2 material that is compositionally uniform and has a hierarchical valence gradient. The nickel valence gradient material shows superior cycling and thermal stability than the conventional one. The result suggests creating an oxidation state gradient that hides the more capacitive but less stable Ni3+ away from the secondary particle surfaces is a viable principle towards the optimization of high-nickel content cathode materials.

Core-Multishell-Structured Digital-Gradient Cathode Materials with Enhanced Mechanical and Electrochemical Durability.

Ni-rich cathode materials provide high energy density, but their structural and surface instability limits their cyclability and thermal stability. As one of the approaches to mitigate this problem, cathode materials comprising Ni-rich high-capacity core wrapped in Mn-rich multiple shells are produced successfully. In contrast to the conventional batch-type process for concentration-gradient materials, a digital-gradient cascade coprecipitation process described here achieves the improvements in productivity and quality consistency needed to move toward large-scale manufacturing. The core-multishell cathode materials produced in this manner not only have longer cycle life and improved rate performance compared to homogeneous Ni-rich cathode materials having the same overall composition, but also show remarkably enhanced thermal stability and low impedance growth characteristics. In a novel attempt to determine the correlation between the mechanical properties of the core-multishell cathode particles and their electrochemical cyclabilities, their breaking force and elasticity were successfully measured using a statistical approach, which indicates that a cathode particle with stable surface composition as well as high breaking force has improved capacity retention and durability. These results guide the realization of long life and high thermal stability in Ni-rich cathode materials through heterogeneous particle engineering.

Enhanced mechanical strength and electrochemical performance of core–shell structured high–nickel cathode material

Improving capacity retention during cycling and the thermal–abuse tolerance of layered high–nickel cathode material, LiNi0.8Mn0.1Co0.1O2 (NMC811), is a significant challenge. A series of core–shell structured cathode materials with the overall composition of LiNi0.8Mn0.1Co0.1O2 was prepared via a coprecipitation method in which the nickel–rich composition (LiNi0.9Mn0.05Co0.05O2) is the core and the manganese–rich composition (LiNi0.33Mn0.33Co0.33O2) is the shell. In terms of achieving a higher nickel content (more than 80%) of heterogeneous material, this core–shell structured material is a more practical approach because it has a larger nickel–rich core region and a thicker manganese–rich shell than the full–concentration gradient material, not to mention being more feasible for continuous mass production. Analysis of mechanical strength through nanoindentation shows that the core–shell structured NMC811 has higher stiffness and compressive stress–strain than the commercial homogeneous NMC811 and retains the mechanical strength and the binding force strong enough to prevent crack formation even after 200 cycles. The prepared core–shell structure NMC811 exhibits a greatly improved capacity retention of 76.6% compared to the commercial homogeneous NMC811 with a capacity retention of 39.6% after 200 cycles. This material also exhibits significantly improved thermal stability over the commercial homogeneous NMC811.

The Correlation between the Particle Morphology and the Electrochemical Stability for High-Ni Cathode and Understanding of the Mechanism of Parasitic Reaction.

Understanding the correlation between physical and electrochemical/chemical properties are significantly crucial for the development of electrode materials for lithium ion batteries. Among the cathode materials, high-Ni cathode with high energy density has a degradation issue of electrochemical performance due to the parasitic reaction at the cathode electrolyte interface. The core-shell or full concentration gradient materials consisting of a high-Ni core and a relatively high-Mn outer layer might be a potential candidate providing the improved electrochemical stability as well as cycle life performance. In this respect, the porosity of the final sintered particle is the key to affect the electrochemical stability indicating the side reaction with organic liquid electrolyte. The strategy tuning the particle porosity and density is applied to synthesize different particle size of transition metal precursor during co-precipitation. The structural characteristics are compared for the materials with different physical properties by utilizing ex-situ or in-situ X-ray diffraction, electron microscopy, electrochemical performances, and particle size distribution. The interfacial kinetic reaction between the Ni-rich cathode and a nonaqueous electrolyte at different SOCs is investigated by our home-built high-precision leakage current measurement system. This study can give us a clear sight for understanding the mechanism of parasitic reaction as well as providing a solution for the safety issue of the high-Ni cathode in lithium ion battery.

Enhancing high-voltage performances of nickel-based cathode material via aluminum and progressive concentration gradient modification

Increasing the average Ni content and extending the working voltage are effective approaches to enhancing the reversible capacity of Li[Ni1−x−yCoxMny]O2 layered oxide cathode materials. However, these would cause severe structural instability and rapid capacity fade upon cycling. In order to address this issue, Al3+ modified novel progressive concentration gradient material Li[Ni0.7Co0.13Mn0.17]O2 is successfully prepared, which maximizes the average Ni content as well as the surficial and structural stability at high cut-off voltage of 4.5 V, attributing to the progressively accelerated transition metals evolution rates from core to surface of the spherical particles and the Al3+ suppressed high-voltage phase transition. Consequently, superior reversible capacity of 206.1 mA h g−1 at 0.1C and capacity retention of 95.7% after 50 cycles at 0.5C rate are obtained, providing skilful approach to obtain promising high-performance cathode materials with both high energy density and long calendar life to satisfy the growing demands of future electric vehicles.

Novel P2-type concentration-gradient Na0.67Ni0.167Co0.167Mn0.67O2 modified by Mn-rich surface as cathode material for sodium ion batteries

Developing rechargeable sodium ion batteries with high capacity and long cycle life is still a big challenge. Herein, we present P2-type concentration-gradient material with average composition of Na0.67Ni0.167Co0.167Mn0.67O2, which exhibits relatively high discharge capacity and excellent stability. The material delivers higher discharge capacity and better rate performance than that of the concentration-constant Na0.67Ni0.167Co0.167Mn0.67O2 during cycling. Also, the material exhibits excellent capacity retention of ∼87% after 100 cycles. The high discharge capacity is attributed to the Ni-rich core and the improvement in cycling stability is due to a gradual and continuous increase of Mn4+ in the concentration-gradient spherical particles. The primary particles on the Mn-rich surface have smaller size than that of the constant-concentration samples, leading to a preferential crystalline state, therefore they can facilitate excellent transport properties for Na ions insertion/extraction process. The P2-type concentration-gradient material provides a new way for the development of advanced sodium ion batteries with high capacity and long cycle life.

The Effect of Tailoring Morphology of Ni-Rich Cathode Oxides on Electrochemical Stability for Lithium Ion Batteries

Understanding the correlation between physical and electrochemical/chemical properties are significantly crucial for development of electrode materials for lithium ion batteries. Among the materials, Ni-rich cathode materials with high energy density has degradation issue of electrochemical performance due to the parasitic reaction at the cathode electrolyte interface. The core-shell or concentration gradient materials consisting of a high-Ni core and a relatively high-Mn outer layer might be potential candidate providing improved stability as well as cycle life performance. In this respect, the porosity of final sintered particle can be an indicator to affect the electrode stability. The strategy to tune the particle porosity is introduced by controlling a feed rate of reactants during co-precipitation synthesis. The structural characteristics was compared for the materials obtained by different feed rate X-ray diffraction, electron microscopy, electrochemical performances, particle size distribution and porosity. The interfacial kinetic reaction between the Ni-rich cathode and a nonaqueous electrolyte at different SOCs is investigated by our home-built high-precision leakage current measurement system. This study can be an indicator for the safety of Ni-rich cathode by co-precipitation.

Constructing a Heterostructural LiNi0.4Mn1.6O4-δ Material from Concentration-Gradient Framework to Significantly Improve Its Cycling Performance.

A heterostructural LiNi0.35Mn1.65O4-δ-LiNi0.5Mn1.5O4 was achieved via constructing the concentration-gradient material with an average composition of LiNi0.4Mn1.6O4-δ. The as-obtained samples were characterized by cross-sectional scanning electron microscopy and energy dispersive X-ray spectrometry, and it was found that the core material LiNi0.35Mn1.65O4-δ is encapsulated completely by a concentration-gradient shell with the outmost layer of LiNi0.5Mn1.5O4. Demonstrated by high resolution transmission electron microscopy and X-ray photoelectron spectroscopy analysis with a low-energy Ar neutral beam etching method, the structurally stable P4332 phase on the surface coordinates the high conductive Fd3̅m phase in the bulk without any detectable interface. At room temperature, the heterostructural samples deliver the initial discharge capacity of 145.1 mAhg-1 at 1 C, close to the theoretical capacity, and the capacity retention after 300 cycles was up to 96.5% of the first discharge capacity. Moreover, it shows excellent rate capability with discharge capacity of 144.3 mAhg-1 at 10 C and significantly improved cycling stability with capacity retention of 85.51% over 50 cycles between 3.0 and 4.95 V at 55 °C. The as-obtained material with coordination of two crystallographic structure domains is a promising cathode to develop high energy, high power, long lifespan, and low cost lithium-ion batteries.

Development of Cathode Materials of Lithium-Ion Secondary Batteries for High Energy and Safety

As a consequence of shortage of fossil fuels, development of electrified vehicles (EVs) has further raised the performance requirements of rechargeable battery system. The research and development efforts in meeting these challenges have focused on identifying and designing new cathode materials with capacity higher than 200 mAh g −1 and improved safety characteristics. In order to improve the thermal and structural stability of the Ni-rich layered cathode materials, cathodes enriched in Mn at the outer layer were proposed to suppress the undesired Ni 4+ reduction because Mn 4+ is naturally stable (MnO2 is a stable compound) and does not participate in the redox reaction during the charge and discharge cycle. Recently, we developed a high-energy cathode material with not only full concentration gradient materials but also two-sloped full concentration gradient materials, in which the Ni concentration decreases and the Mn concentration increases toward the particle surface. These cathode materials are synthesized via a specially designed batch-type reactor. The cathode delivers high discharge capacity with excellent capacity retention. The cathode materials exhibits the best cycling stability, rate capability, and thermal stability compared to conventional cathode (CC) and Li[Ni0.8Co0.15Al0.05]O2 (NCA). While the chemical partitioning of the composition generated the observed high capacity and thermal stability, the unique microstructure of the FCG secondary particle provided excellent cycle stability and rate capability.

Nanorod Assembly in a Spherical Secondary Particle for High-Energy Sodium Ion Batteries

Nowadays, to adjust the fluctuations in electricity production and efficient use of midnight off-peaks for stable energy supply, the mid-large scale battery system has been growing up. In particularly, sodium ion batteries have many interests as an alternative candidate for cost-advantage versus lithium ion batteries because of large amounts of reservation of sodium resources in earth. However, intrinsic structural disadvantage of interstitial tetrahedral sites dissimilar to the O3 structure led to the low discharge capacity and cycle retentions and it have not yet satisfactorily addressed. Recently, to breakthrough present drawbacks, we suggested the new concept of radially aligned hierarchical columnar structure with varied chemical composition To further study of novel nano-structured with varied chemical composition materials, we carry out the synthesis and characterization of O3-type layered structure cathode material of constant concentration and full concentration gradient material. Through the comparison of electrochemical properties and related structural properties, herein, we investigated and defined the novel concept FCG materials. Especially, we focus on the effect of particle morphology and micro structured properties by using various analysis technique. Micro-compression testing and single particle electrochemical measurement results demonstrate the robustness of the spherical particles and the associated Na+ ion mobility in the particles. These significant improvements provided by the tailored structure are appealing for utilizing sodium ion. We believe that the unexplored site of radially assembled nano-rod structure primary particles having varied chemical composition is highly contribute to high power and high energy Na-ion battery systems.

Quaternary phase diagrams of spinelLiy□1−yMnxNi2−xO4and composite cathode voltages for concentration gradient materials

Core-shell coating structures and concentration gradient materials may enhance Li-ion battery performance by integrating advantages of core and shell components without introducing unfavorable problems associated with general coatings. The fundamental thermodynamic properties of concentration gradient composite materials are complex due to the multicomponent nature of the problem. We systematically study the thermodynamics of ordering and phase separation in the quaternary spinel ${\mathrm{Li}}_{y}{\ensuremath{\square}}_{1\ensuremath{-}y}{\mathrm{Mn}}_{x}{\mathrm{Ni}}_{2\ensuremath{-}x}{\mathrm{O}}_{4}$ ($\ensuremath{\square}$ means vacancy) system by density functional theory calculations, together with the coupled cluster expansion method with interactions within and between (Li/$\ensuremath{\square}$) and (Mn/Ni) sublattices. On the basis of coupled cluster expansion interactions and Monte Carlo simulations, we calculate quaternary phase diagrams as a function of temperature as well as voltage profiles of single ordered phases and multiphase composite structures. The phase diagram and voltage results are in good agreement with available experimental observations. We also predict a stable high-voltage ordered compound ${\mathrm{LiMnNiO}}_{4}$, with a very high delithiation voltage of 4.76 V. For the composite (Mn-$\text{rich}+\text{Ni}$-rich) cathode materials, the voltage profiles show combinations of plateaus from each component compound. The computational strategy of combining quaternary phase diagrams with voltage calculations provides a pathway to understand and design concentration gradient materials.

Tailoring Nickel-Rich LiNi0.8Co0.1Mn0.1O2 Cathode Material with LiNi0. 4Co0. 2Mn0. 4O2 Surface Composition

Nickel-rich cathode material, LiNi0.8Co0.1Mn0.1O2, exhibits high specific capacity of approximately 200 mAh/g-oxide and potential for use in plug-in hybrid electric vehicles. However, significant challenges remain to improve the cycle life and thermal-abuse tolerance of this material. To improve the stability of this material, several researchers have investigated a core-shell approach resulted in a nickel-rich LiNi0.8Co0.1Mn0.1O2 core and a manganese-rich LiNi0.5Mn0.5O2shell for surface stabilization [1]. However, the structural mismatch between the core and shell compositions leads to large void formation at the core-shell interface which triggers a sudden drop in capacity after long-term cycling. To overcome the volume change between the core and shell compositions, concentration gradient shell was investigated [2] and full concentration gradient material was suggested which shows the gradual decrease of nickel concentration and increase of manganese concentration from the centre towards the outer layer of the particle [3]. Even though many researchers showed the promising high energy, long calendar life and excellent abuse tolerance of core-shell, core-concentration gradient shell and full concentration gradient materials by their synthesis optimization, the compared nominal composition of LiNi0.8Co0.1Mn0.1O2 was not well-optimized. Here, we report the optimized synthesis condition of a nominal composition of LiNi0.8Co0.1Mn0.1O2, core-shell and core-concentration gradient shell materials with LiNi0.4Co0.2Mn0.4O2 surface composition. The detailed comparison of the physical and electrochemical properties of the prepared materials will be discussed. References Y.-K. Sun, S.-T. Myung, M.H. Kim, J. Prakash and K. Amine, J. Am. Chem. Soc. 127(38), 13411 (2005). Y.-K. Sun, S.-T. Myung, B.-C. Park, J. Prakash, I. Belharouak and K. Amine, Nature Mater. 8, 320 (2009). Y.-K. Sun, Z. Chen, H.-J. Noh, D.-J. Lee, H.-G. Jung, Y. Ren, S. Wang, C.S. Yoon, S.-T. Myung and K. Amine, Nature Mater. 11, 942 (2012).

Controlled synthesis of concentration gradient LiNi0.84Co0.10Mn0.04Al0.02O1.90F0.10 with improved electrochemical properties in Li-ion batteries

Ion exchange method is adopted to design the concentration gradient materials for Li-ion batteries.

Concentration-gradient LiMn0.8Fe0.2PO4 cathode material for high performance lithium ion battery

It is a great challenge to combine good cycling performance with high rate capability for LiMn1–xMxPO4 cathode materials owing to the Mn dissolution upon cycling and its low electronic/ionic conductivity. Here, we report a novel concentration-gradient structure of LiMn0.8Fe0.2PO4 material constructed by solvothermal treatment. This material shows a linear increase of Mn concentration from the edge to the particle centre, but the inverse trend for Fe concentration, which leads to the formation of Mn-rich phase in bulk and Fe-rich phase at surface. The Fe-rich phase effectively suppresses the corrosion from the electrolyte that minimizes the Mn dissolution and also improves the electronic/ionic conductivity of the surface that decreases the cathode/electrolyte interface resistance. Consequently, this concentration-gradient material achieves superior capacity retention with 98% after 50 cycles at 1 °C even at elevated temperature, and also exhibits an excellent rate capability with the reversible capacity of 130 mA h g−1 at 5 °C rate. These results suggest that the concentration-gradient LiMn0.8Fe0.2PO4 is an ideal type of cathode material for high performance Lithium ion batteries.

A Nanostructured Cathode Material with Varied Chemical Composition for High Energy Density Sodium Ion Batteries

Lithium batteries currently dominate the secondary battery market because of their high energy and good power density.[1] Despite their feasibility, the mass production of such large-scale batteries would likely contribute to the future exhaustion of limited lithium resources. This concern has led us to look for alternative systems to replace current lithium-related chemistries. Because of sodium’s abundance in nature, sodium-based rechargeable batteries have recently received intensive attentions [2]Our prior works36,37, we suggested that the nanorod-structured full concentration gradient materials are beneficial in performing outstanding electrochemical properties and excellent safety in lithium-ion batteries system, because the dense rod assembly could minimize surface area contacting with electrolyte.[3] We introduce a new concept: a radially aligned hierarchical columnar structure (RAHC) in spherical particles with varied chemical composition from the inner end (Na[Ni0.75Co0.02Mn0.23]O2) to the outer end (Na[Ni0.58Co0.06Mn0.36]O2) of the structure.Using this concept, we suggest that an electrochemical reaction based on Ni2+/3+/4+ is readily available to deliver a high discharge capacity of 157 mAh (g-oxide)-1 (15 mA g-1), an excellent capacity retention of 80% (125 mAh g-1) during 300 cycles in combination with a hard carbon anode, and a reasonable rate capability of 132.6 mAh g-1 (1500 mA g-1, 10 C-rate). In addition, the RAHC electrode exhibits good temperature performance even at -20°C. The chemistry of the RAHC material, which utilizes the Ni redox reaction and minimizes the surface area contacting corrosive electrolyte, is responsible for the excellent electrochemical properties and the satisfactory thermal stability, which exhibits a main exothermic reaction at 293.5oC with low heat generation. References (1) Scrosati, B. & Garche, J. Lithium batteries: status, prospects and future. J. Power Sources 195, 2419 (2010). (2) Stevens, D. A., Dahn, J. R. High capacity anode materials for rechargeable sodium-ion batteries. J. Electrochem. Soc. 147(4), 1271 (2000). (3) Sun, Y.-K. et al. Nanostructured high-energy cathode materials for advanced lithium batteries. Nat. Mater. 11, 942 (2012).

Electrochemical Performance of Full Concentration Gradient Cathode for Lithium-Ion Batteries

Worldwide effort is being devoted to development of lithium-ion batteries for consumer devices, plug-in hybrid electric vehicles (PHEVs) and all-electric vehicles (EV), which require higher energy, increased safety, and lower cost. Most commercial lithium-ion batteries use a layered LiCoO2 as the cathode material, but LiCoO2has a limited practical capacity of about 140 mAh/g. A high capacity cathode material with high packing density is thus being sought to improve the energy density of lithium-ion batteries with improved safety. Recently, some novel design structures cathode material are reported, such as core-shell, gradient material. First, a co-precipitation process is used to synthesize core-shell or gradient structure spherical precursor, then using this precursor to prepare a same structure cathode material. Using this new process, it is easy to control the elements distribution inside of single particles. This concept make it is possible to achieve the high capacity, cycling life and safety for a cathode material. So the composition design is based on those, high Ni in bulk material for high capacity and high Mn on the surface for safety with certain Co are investigated. In this study, we investigated a full concentration gradient material, and the average composition is closed to Li1.0Ni0.6Co0.2Mn0.2O2. The material was synthesized by a solid-state reaction from full concentration gradient spherical precursor Ni0.6Co0.2Mn0.2(OH)2 and LiOH precursors. The full concentration gradient spherical precursor Ni0.6Co0.2Mn0.2(OH)2was prepared by a co-precipitation process. It exhibited uniform spherical particle shape with 15-mm diameter and high tap density of 2.7 g/cc. The electrochemical performance of the material was evaluated in a coin-cell. When the current density was 16 mA/g (C/10), the discharge capacities were about 191 mAh/g. The significant improvement in tap density and the high capacity of this material makes it a potential cathode material for high energy battery application. Acknowledgments The authors acknowledge the financial support of the U.S. Department of Energy, FreedomCAR & Vehicle Technologies Office, under Contract No. DE-AC02-06CH11357. Figure 1

Study of full concentration-gradient Li(Ni0.8Co0.1Mn0.1)O2 cathode material for lithium ion batteries

A high-energy full concentration-gradient cathode material with an average composition of Li(Ni0.8Co0.1Mn0.1)O2 has been successfully synthesized by a hydroxide co-precipitation method. Ni content decreases gradually along the radius of the spherical particle, and the content of Co and Mn increases. The electrochemical properties of this concentration-gradient material are studied and compared to those of the homogeneous Li(Ni0.8Co0.1Mn0.1)O2 material. In the concentration-gradient material of Li(Ni0.8Co0.1Mn0.1)O2, the inside part rich in Ni delivers a very high capacity, while the Mn-rich outside part improves the cycling stability and rate performance. The concentration-gradient material has superior electrochemical properties compared to the homogeneous material. The initial capacity of the concentration-gradient Li(Ni0.8Co0.1Mn0.1)O2 is 185.2mAhg−1 at 1 C between 2.8 and 4.3V and retains 93.2% after 100 cycles. The composite also has a good rate performance with a high capacity of about 175mAhg−1 even at 2C rate.