Full Concentration Gradient Research Articles

Improved Performances of Li[Ni0.65Co0.08Mn0.27]O2 Cathode Material with Full Concentration Gradient for Li-Ion Batteries

Full concentration gradient (FCG) cathode material having nickel-rich core Li[Ni0.89Co0.01Mn0.10]O2 and nickel-deficient outer layer Li[Ni0.61Co0.09Mn0.30]O2 was synthesized via co-precipitation method. A smoothly varying concentration gradients for Ni, Co, and Mn extended from the core to the surface within a single cathode particle with an average composition of Li[Ni0.65Co0.08Mn0.27]O2. Electrochemical and thermal properties of the FCG cathode were evaluated and compared to the conventional cathode (CC) material, Li[Ni0.65Co0.08Mn0.27]O2 without the concentration gradient. The BET surface area measurement demonstrated the presence of densely agglomerated primary particles in the FCG cathode. Owing to the unique spatial distribution of the cations and particle morphology, the FCG cathode delivered higher discharge capacity, superior cycle stability and excellent thermal stability compared to the CC Li[Ni0.65Co0.08Mn0.27]O2 .

High-Energy Layered Oxide Cathodes with Thin Shells for Improved Surface Stability

Core–shell, nickel-rich layered oxide materials with a full concentration gradient (FCG) core and thin shells with low nickel content have been investigated. Hierarchically structured core–shell materials have the same FCG core, where the composition gradually changes from Li[Ni0.86Co0.07Mn0.07]O2 to Li[Ni0.67Co0.09Mn0.24]O2 from the center to the outer surface. A thin shell composed of either Li[Ni0.48Co0.26Mn0.26]O2 or Li[Ni0.56Co0.18Mn0.26]O2 was applied to the outer surface of the FCG core. This hierarchical core–shell structure efficiently integrates the benefit of high energy from the Ni-rich core, structural stability and favorable transport of Li+ ions from the FCG core, and surface stability from the low-Ni and high-Mn shell. The core–shell cathodes demonstrate improved cycling performance at 55 °C even up to 4.5 V when compared to the FCG core-only cathode. Shells of low nickel content and a thickness of ∼300 nm provide sufficient surface stability, particularly at elevated temperatures. We sugg...

Effect of outer layer thickness on full concentration gradient layered cathode material for lithium-ion batteries

Full concentration gradient (FCG) layered cathode materials Li[Ni0.6−xCo0.15+xMn0.25]O2 (x = 0, 0.01, and 0.04) with different outer layer thicknesses are synthesized via a specially developed coprecipitation method. In the FCG cathode, the nickel concentration decreases linearly and the cobalt concentration increases from the center to particle surface throughout the particle at a fixed composition of Mn. The thickness of the FCG primary particle increases in the radial direction with an increasing outer layer thickness of the secondary particles and significantly affects the electrochemical performance. An increase in the stable outer layer thickness improves the cycle performance and thermal stability of the FCG materials at the expense of reversible capacity, whereas the rate capability and low temperature performance are significantly deteriorated by increasing outer layer thickness. All of the FCG materials exhibit superior electrochemical and thermal properties compared to the conventional cathode Li[Ni0.58Co0.17Mn0.25]O2 due to the unique microstructure of the FCG cathode.

Effect of Fixed Mn Content in Full Concentration Gradient Structure on the Electrochemical Properties of Layered Cathode Materials

Introduction The lithium batteries are being developed as power sources for plug-in hybrid electric and electric vehicles, and for these applications, high energy cathodes are necessary to reduce battery size because the mounting space is significantly limited.[1] Hence, layered lithium nickel-cobalt-manganese oxide, Li[NixCoyMnz]O2 (x + y + z = 1), which delivers a high discharge capacity of over 170 mAh g− 1, has been intensively studied for high energy density lithium-ion batteries.[2] However, these cathodes exhibit some serious problems, such as capacity fade and poor thermal stability, which hinder their use in vehicle applications. In particular, oxygen evolution from the delithiated cathode can cause serious safety concerns. These limitations necessitate the development of new materials to resolve the above-mentioned difficulties.Recently, we introduced unique materials, which have a core−shell (core with gradient shell) or full concentration gradient (FCG) structure in a particle level.[3] The structure is basically composed of a Ni-rich core that delivers high capacity and a Mn-rich shell that provides outstanding thermal stability. Our latest report included a new type of FCG material composed of long rod-shaped primary particles approximately 2.5 μm in length,[4] which demonstrated good electrochemical performance and excellent thermal properties due to lower grain boundary resistance ascribed to lower specific surface area contacting with the electrolyte during cycling. However, the Mn concentration could not be varied because of the difficulty of the rod-shaped particle synthesis.Here, we report the design of FCG Li[NixCo0.16Mn0.84−x]O2 (x = 0.64, 0.59, and 0.51) cathode materials with fixed Mn contents of 20, 25, and 33% in the transition-metal layer. We also report the effects of Mn concentration in terms of structural, electrochemical, and thermal characteristics of the FCG materials. Experimental Spherical FCG [NixCo0.16Mn0.84-x](OH)2 (x = 0.51, 0.59, and 0.64) precursors were synthesized by a coprecipitation method. A Ni-poor aqueous solution (molar ratio of Ni:Co:Mn = 0.47:0.20:0.33, 0.55:0.20:0.25, 0.60:0.20:0.20,), consisting of NiSO4·6H2O, CoSO4·7H2O, and MnSO4·5H2O as starting materials, was slowly pumped from tank 2 into a Ni-rich (molar ratio of Ni:Mn = 0.67:0.33, 0.75:0.25, 0.80:0.20) stock solution in tank 1. The homogeneously mixed solution was then fed into a continuously stirred tank reactor (CSTR, 4 L) in a replenished N2 atmosphere. Simultaneously, a 3.0 mol L- 1 NaOH solution (aq.) and the desired amount of a NH4OH chelating agent solution (aq.) were pumped separately into the reactor. The concentration of the solution, pH, temperature, and stirring speed of the mixture in the reactor were carefully controlled. During the early stage of the coprecipitation process, Ni-rich hydroxide (center composition) first precipitated. Nickel-cobalt-manganese hydroxide of different compositions then gradually layered onto the initially formed [NixCo0.16Mn0.84 − x](OH)2 (x = 0.51, 0.59, and 0.64) particles, resulting in a linear composition change of Ni and Co toward the outer surface of the particles. Precursor powders were obtained through filtering, washing, and drying at 100 °C overnight. The obtained FCG [NixCo0.16Mn0.84 − x](OH)2 (x = 0.51, 0.59, and 0.64) was mixed with LiOH·H2O, and the mixture was calcined at various temperatures for 10 h in air: 780 °C for Li[Ni0.64Co0.16Mn0.20]O2, 845 °C for Li[Ni0.59Co0.16Mn0.25]O2, and 920 °C for Li[Ni0.51Co0.16Mn0.33]O2.The chemical compositions of the resulting powders were determined by atomic absorption spectroscopy (AAS, Vario 6, Analyticjena). Line scans for the full-gradient materials were obtained with an electron probe X-ray microanalyzer (EPMA, JXA-8100, JEOL). Results and discussion To judge the relative merits of the FCG Li[NixCo0.16Mn0.84 − x]O2 cathodes, coin-type half-cells were tested at 55 °C and C-rates of 0.1 and 0.5 (20.6 and 102.8 mA g− 1) with a cutoff voltage of 4.3 V, and the results are presented in Figure 1. The trend observed at 25 °C was similarly found for cycling at the elevated temperature. The Li[Ni0.64Co0.16Mn0.20]O2 cell againdelivered the highest initial capacity of 201.7 mAh g− 1 and exhibited the worst capacity retention, whereas the Li[Ni0.51Co0.16Mn0.33]O2 cathode with the lowest discharge capacity of 184.8 mAh g− 1 best retained its initial capacity after 100 cycles. It is generally known that a high Mn content in Li[NixCoyMn1 − x − y]O2 is detrimental to the rate capability of the Li-ion battery.Figure 1. Initial charge-discharge curves of the FCG Li[NixCo0.16Mn0.84-x]O2 (x = 0.51, 0.59, and 0.64) (a) between 2.7 and 4.3 V at 55 °C (current density of 0.1 C-rate corresponds to 20.6 mA g- 1). Corresponding cycling performance of half-cells (b) between 2.7 and 4.3 V at 55 °C by applying a constant current of 0.5-C rate (102.8 mA g- 1).

Optimization of Full Concentration Gradient Li[NixCo0.16Mn0.84-X]O2 (x=0.64, 0.59, 0.51) Cathode Material for Lithium-Ion Batteries

Lithium batteries are being developed as power sources for plug-in hybrid electric and electric vehicles, and for these applications, high energy cathodes are necessary to reduce battery size because the mounting space is significantly limited (1-2). However, these cathodes exhibit some serious problems such as capacity fade and poor thermal stability, which hinders their use in vehicle applications. In particular, oxygen evolution from the delithiated cathode can cause serious safety concerns. These limitations necessitate the development of new materials to resolve the above-mentioned difficulties. Recently, we introduced unique materials, which have a core-shell (core with gradient shell) or full concentration gradient (FCG) structure in a particle level (3). The structure is basically composed of a Ni-rich core that delivers high capacity and a Mn-rich shell that provides outstanding thermal stability. However, the Mn concentration could not be varied because of the difficulty of the rod-shaped particle synthesis.We report the design of FCG Li[NixCo0.16Mn0.84-x]O2 (x = 0.64, 0.59, and 0.51) cathode materials with fixed Mn contents of 20, 25, and 33% in the transition metal layer. These cathode materials with concentration gradients followed the general performance trend of conventional layered materials; an increase in Ni content improved the capacity, whereas a higher amount of Mn delivered better capacity retention and thermal properties at the expense of capacity. We also report the effects of Mn concentration in terms of structural, electrochemical, and thermal characteristics of the FCG materials. As a result, we determined an optimal level of Mn concentration among the tested FCG cathodes, which maximized the discharge capacity of 188 mAh g-1 and had an excellent capacity retention of 96 % over 100 cycles operated up to 4.3 V at 25 oC, with a composition of FCG Li[Ni0.59Co0.16Mn0.25]O2.Reference1. J. B. Goodenough, Y. Kim, Chem. Mater.22 (2010) 5872. V. Etacheri, R. Marom, R. Elazari, G. Salitra, D. Aurbach, Energy Environ. Sci.4 (2011) 32433. Y.-K. Sun, S.-T. Myung, M.-H. Kim, J. Prakash, K. Amine, J. Amer. Chem. Soc. 127 (2005) 13411

High-Energy Li-Ion Battery with Long Cycle Life Comprising Silicon-Based Anode and Layered Composite Cathode

Currently, high-energy lithium ion batteries are in unprecedented demand for use in various energy storage applications including emerging electronic devices and a series of electrified vehicles. In this study, high capacity electrodes based on a Si composite anode and a layered composite oxide cathode, Ni-rich Li[Ni0.75Co0.1Mn0.15]O2, were evaluated and combined to fabricate a high energy lithium ion battery. The Si composite anode, Si/C-IWGS (Si/C composite internally wired with graphene sheets), was prepared by a scalable sol-gel process. The Si/C-IWGS anode delivered a high capacity of >800 mAh g-1 with excellent cycling stability up to 200 cycles mainly due to the small amount of graphene (i.e., ~6 wt%), which was ideally dispersed to maintain an electrical network in the composite against large volume changes. The cathode (Li[Ni0.75Co0.1Mn0.15]O2) was structurally optimized (Ni-rich core and a Ni-depleted shell with a continuous concentration gradient between the core and shell, i.e., full concentration gradient, FCG, cathode) so as to deliver a high capacity (>200 mAh g-1) with excellent stability at high voltage (~4.3 V). A novel lithium ion battery system based on the Si/C-IWGS anode and FCG cathode successfully demonstrated a high energy density (240 Wh kg-1 at least) as well as an unprecedented excellent cycling stability up to 750 cycles between 2.7 and 4.2 V at 1 C. As a result, the novel battery system can be an attractive candidate for energy storage applications demanding a high energy density and long cycle life.

Invited Presentation: High-Energy Cathode Material for Advanced Lithium-Ion Batteries

A great attention has been made on development of lithium-ion batteries with high energy density and long cycle life for automotive applications such as plug-in hybrid vehicles (PHEVs) and electric vehicles (EV). A successful use in the automotive sectors, where both energy density and safety is of great importance, requires further increase in energy density, cycle life, and safety. Meeting this challenge has centered on finding new cathode materials with high capacity and excellent safety which is the major factor deciding for the real battery applicationsOne of the promising candidates for such batteries, Li[Ni0.8Co0.1Mn0.1]O2 (Ni-rich NCM) and Li[Ni0.8Co0.15Al0.05]O2 (NCA) have been studied extensively for the last decade [1,2]. Though these materials deliver high capacity of 200 mAh g-1 (4.3 V cutoff voltage), they exhibit very poor thermal characteristics and cycling stability, particularly elevated temperature]. One of the most promising oxides is a core-shell (with gradient) [3] or full concentration gradient lithium nickel-cobalt-manganese oxide [4] composed of a Mn-rich outer surface providing excellent safety and Ni-rich center achieving high capacity. This new approach has made it possible to design and develop materials with different gradient compositions and slopes within a particle.In this presentation, we report a novel cathode material with two slope full concentration gradients (TSFCG) of Ni, Co, and Mn ions extending throughout each particle to increase average active redox species of Ni concentration and the lower Mn concentration in the particle outer surface. The Ni-rich TSFCG delivers a high capacity of more than 200 mAh g-1 (4.3 V cutoff voltage) with excellent cycle life and good thermal properties. Furthermore, the electrochemical and thermal properties of the TSFCG were compared with those of NCA and conventional cathode (C.C.).

Comparison of Full Concentration Gradient Li[Ni0.54Co0.16Mn0.30]O2 with Conventional Cathode Materials for Li-Ion Batteries

Lithium-ion batteries are an important power source owing to their high energy density, high voltage, and excellent cycle life. Common applications include portable electronic devices such as portable smart phones, notebook-style personal computers, plug-in hybrid vehicles (PHEVs), and electric vehicles (EVs). However, the energy density and safety of lithium-ion batteries is still insufficient for most applications. At present, the driving range of EVs is less than 160 km and is significantly reduced by the use of air conditioning. As a result, further increases in the energy density, cycle life, and safety are important for their successful application in the automobile industry. The development of new, high-capacity cathode materials is a prerequisite for the next generation of lithium-ion batteries intended for use in EV applications.[1–2]The layered Li[NixCoyMnz]O2 materials, only Li[Ni1/3Co1/3Mn1/3]O2 is used in automobile applications in conjunction with stabilized spinel Li1 + xMn2 - yAlyO4 in a composite form, resulting in a lower capacity and outstanding safety characteristics characteristics.[3] The capacity of Li[Ni1/3Co1/3Mn1/3]O2 (155 mAh g- 1) is so low that it limits the driving range of associated EVs to less than 160 km. Another promising cathode material is Li[Ni0.5Co0.2Mn0.3]O2, which delivers a capacity of 170 mAh g- 1. However, Li[Ni0.5Co0.2Mn0.3]O2 fails to satisfy requirements for EV applications owing to its poor capacity retention and safety, creating a need for cathode materials with the capacity of Li[Ni0.5Co0.2Mn0.3]O2 and the safety of Li[Ni1/3Co1/3Mn1/3]O2.We report a promising cathode material specifically engineered for EV applications: Li[Ni0.54Co0.16Mn0.30]O2 with a full concentration gradient (FCG) of Ni and Co ions at a fixed Mn content of 30% throughout the particle. We compared the electrochemical, structural, and thermal stabilities of the FCG material with those of conventional Li[Ni0.5Co0.2Mn0.3]O2 and Li[Ni1/3Co1/3Mn1/3]O2materials. Experimental Spherical FCG [NixCoyMnz](OH)2 precursors were synthesized through the co-precipitation method. A Ni-poor aqueous solution (molar ratio of Ni/Co/Mn = 0.50:0.20:0.30) consisting of NiSO4·6H2O, CoSO4·7H2O, and MnSO4·5H2O was slowly pumped from tank 2 into a Ni-rich (molar ratio of Ni/Mn=0.7:0.3) stock solution in tank 1. The homogeneously mixed solution was then fed into a continuously stirred tank reactor (CSTR, 4 L) in a replenished N2 atmosphere. Concurrently, a NaOH solution (4.0 mol L- 1, aq) and the desired amount of a NH4OH chelating agent solution (aq) were pumped separately into the reactor. The concentration of the solution, pH value, temperature, and stirring speed of the mixture in the reactor were carefully controlled. During the early stage of the co-precipitation process, [Ni0.7Mn0.3](OH)2 (composition of the center of the particle) was first precipitated. Nickel–cobalt–manganese hydroxide at different compositions was then gradually piled onto the formed [Ni0.7Mn0.3](OH)2 particles to result in a linear composition change of Ni and Co toward the outer surface of the particles. The precursor powders were obtained through filtering, washing, and drying at 100 oC overnight. The obtained FCG [Ni0.54Co0.16Mn0.30](OH)2 was mixed with LiOH·H2O, and the mixture was calcined at 875 oC for 10 h in air.Electrochemical properties of the synthesized FCG [Ni0.54Co0.16Mn0.30]O2 were evaluated using a 2032-type coin type cell. Results and discussion Fig. 1 shows the change of concentrations of Co and Ni in the single rod-shaped primary particle was determined by means of energy-dispersive X-ray spectroscopy (EDS) along with the corresponding elemental distribution of Ni, Co, and Mn around the center region of the FCG particle; the results are shown superimposed on the TEM image. The EDS data show that the Co/Ni atomic ratio decreased from 0.375 to 0.323 along the 1.2 mm length toward particle core, a composition variation similar to that shown by the electron-probe X-ray microanalysis (EPMA) data in Figure 2. Note that the concentration gradient was observed within a single primary particle, which is a characteristic of the FCG particles synthesized by our unique co-precipitation method. Ni was depleted at the particle surface and became slowly enriched toward the particle center whereas Co levels gradually depleted. As expected, the elemental mapping shows that Mn was distributed uniformly throughout the center region of particle.

A High‐Energy Li‐Ion Battery Using a Silicon‐Based Anode and a Nano‐Structured Layered Composite Cathode

High capacity electrodes based on a Si composite anode and a layered composite oxide cathode, Ni‐rich Li[Ni0.75Co0.1Mn0.15]O2, are evaluated and combined to fabricate a high energy lithium ion battery. The Si composite anode, Si/C‐IWGS (internally wired with graphene sheets), is prepared by a scalable sol–gel process. The Si/C‐IWGS anode delivers a high capacity of >800 mAh g−1 with an excellent cycling stability of up to 200 cycles, mainly due to the small amount of graphene (∼6 wt%). The cathode (Li[Ni0.75Co0.1Mn0.15]O2) is structurally optimized (Ni‐rich core and a Ni‐depleted shell with a continuous concentration gradient between the core and shell, i.e., a full concentration gradient, FCG, cathode) so as to deliver a high capacity (>200 mAh g−1) with excellent stability at high voltage (∼4.3 V). A novel lithium ion battery system based on the Si/C‐IWGS anode and FCG cathode successfully demonstrates a high energy density (240 Wh kg−1 at least) as well as an unprecedented excellent cycling stability of up to 750 cycles between 2.7 and 4.2 V at 1C. As a result, the novel battery system is an attractive candidate for energy storage applications demanding a high energy density and long cycle life.

Optimization of Layered Cathode Material with Full Concentration Gradient for Lithium-Ion Batteries

Li[NixCoyMn1–x–y]O2 cathode materials were synthesized with varying concentration gradients of Ni and Co ions from the particle center (0.62–0.74 mol % for Ni and 0.05 mol % for Co) to the surface (0.48–0.62 mol % for Ni and 0.18 mol % for Co), i.e., full concentration gradient (FCG) with fixed Mn concentrations. In particular, the Mn concentration (20, 25, and 33 mol %) was controlled to optimize electrode performance. The average chemical compositions of lithiated products were Li[NixCo0.16Mn0.84–x]O2 (x = 0.64, 0.59, 0.51). These cathode materials with concentration gradients followed the general performance trend of conventional layered materials; an increase in Ni content improved the capacity, whereas a higher amount of Mn delivered better capacity retention and thermal properties at the expense of capacity. As a result, we determined an optimal level of Mn concentration among the tested FCG cathodes, which maximized the discharge capacity of 188 mAh g–1 and had an excellent capacity retention of 96...

Comparison of Nanorod‐Structured Li[Ni0.54Co0.16Mn0.30]O2 with Conventional Cathode Materials for Li‐Ion Batteries

We successfully synthesized a safe, high-capacity cathode material specifically engineered for EV applications with a full concentration gradient (FCG) of Ni and Co ions at a fixed Mn content throughout the particles. The electrochemical and thermal properties of the FCG Li[Ni(0.54)Co(0.16)Mn(0.30)]O2 were evaluated and compared to those of conventional Li[Ni(0.5) Co(0.2) Mn(0.3)]O2 and Li[Ni(1/3)Co(1/3)Mn(1/3)]O2 materials. It was found that the FCG Li[Ni(0.54)Co(0.16)Mn(0.30)]O2 demonstrated a higher discharge capacity and a superior lithium intercalation stability compared to Li[Ni(0.5) Co(0.2)Mn(0.3)]O2 and Li[Ni(1/3)Co(1/3)Mn(1/3)]O2 over all of the tested voltage ranges. The results of electrochemical impedance spectroscopy and transition-metal dissolution demonstrate that the microstructure of primary particle with rod-shaped morphology plays an important role in reducing metal dissolution, which thereby decreases the charge transfer resistance as a result of stabilization of the host structure.

Cathode Material with Nanorod Structure—An Application for Advanced High-Energy and Safe Lithium Batteries

We have developed a novel cathode material based on lithium–nickel–manganese–cobalt oxide, where the manganese concentration remains constant throughout the particle, while the nickel concentration decreases linearly and the cobalt concentration increases from the center to the outer surface of the particle. This full concentration gradient material with a fixed manganese composition (FCG–Mn-F) has an average composition of Li[Ni0.60Co0.15Mn0.25]O2 and is composed of rod-shaped primary particles whose length reaches 2.5 μm, growing in the radial direction. In cell tests, the FCG–Mn-F material delivered a high capacity of 206 mAh g–1 with excellent capacity retention of 70.3% after 1000 cycles at 55 °C. This cathode material also exhibited outstanding rate capability, good low-temperature performance, and excellent safety, compared to a conventional cathode having the same composition (Li[Ni0.60Co0.15Mn0.25]O2), where the concentration of the metals is constant across the particles.