Double-Shell Type Gradient Ni-Rich LiNi0.76Co0.10Mn0.14O2

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A Core/double-shell Type Gradient Ni-rich LiNi0.76Co0.10Mn0.14O2 with High Capacity and Long Cycle Life for Lithium-ion Batteries Jin-Yun Liao, Seung-Min Oh, and Arumugam Manthiram ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b06172 • Publication Date (Web): 29 Aug 2016 Downloaded from http://pubs.acs.org on August 31, 2016

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ACS Applied Materials & Interfaces

A Core/double-shell Type Gradient Ni-rich LiNi0.76Co0.10Mn0.14O2 with High Capacity and Long Cycle Life for Lithium-ion Batteries Jin-Yun Liao, Seung-Min Oh, and Arumugam Manthiram* Materials Science and Engineering Program and Texas Materials Institute, The University of Texas at Austin, Austin, TX78712, USA

KEYWORDS: Lithium-ion batteries; layered oxide cathode, nickel-rich oxide; core/doubleshell structure; concentration-gradient oxides; high loading electrodes

ABSTRACT: A concentration-gradient Ni-rich LiNi0.76Co0.1Mn0.14O2 layered oxide cathode has been developed by firing a core/double-shell [Ni0.9Co0.1]0.4[Ni0.7Co0.1Mn0.2]0.5[Ni0.5Co0.1Mn0.4]0.1(OH)2 hydroxide precursor with LiOH∙H2O, where the Ni-rich interior (core) delivers high capacity and the Mn-rich exterior (shells) provides a protection layer to improve the cyclability and thermal stability for the Ni-rich oxide cathodes. The content of nickel and manganese, respectively, decreases and increases gradually from the center to the surface of each gradient sample particle, offering a high capacity with enhanced surface/structural stability and cyclability. The obtained concentration-gradient oxide cathode exhibits high energy density with long cycle life in both half- and full- cells. With high-loading electrode half-cells, the CG sample delivers 3.3 mA h cm-2 with 99% retention after 100 cycles. The material morphology, phase, and gradient structure are also maintained after cycling. The pouch-type full cells fabricated with a graphite anode delivers high capacity with 89% capacity retention after 500 cycles at C/3 rate.

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1. INTRODUCTION The Ni-rich layered oxides LiNixCoyMnzO2 with x > 0.5 have been drawing much attention1,2 for lithium-ion batteries (LIBs) due to their high energy density and low cost.3-9 With a high Ni content of > 0.7, the nickel-rich layered oxides have the potential to deliver a practical capacity of over 220 mA h g-1 at a reasonably high operating voltage of 3.6 – 4.6 V.10,11 More importantly, unlike the lithium-rich layered oxides, the nickel-rich layered oxides do not undergo layered to spinel phase transition during cycling.9,12 The nickel-rich layered oxides thus have the potential to be the next-generation high-energy-density cathode that can enable the electric vehicles (EVs) market. However, the nickel-rich layered oxide cathodes suffer from capacity fade during cycling. When the Ni-rich oxides are charged above 4.3 V, they exhibit aggressive side reactions with the organic electrolyte because of the unstable tetravalent nickel in charged state, resulting in poor cycle life.13-15 Recent research efforts on Ni-rich layered oxide cathodes have focused on surface and structural modifications to realize controlled bulk and/or surface compositions to suppress the capacity fade. To date, surface coating with different materials, including carbon,16 metal oxides (Al2O3),17,18 metal fluoride (AlF3),19 and metal phosphates (AlPO4)20,21 have been reported to improve the cycling performance and thermal stability of Ni-rich layered oxides cathodes. The improvements offered by surface coating can mainly be attributed to the protective thin layer on the surface of the active material to restrain the undesired side reactions between the unstable tetravalent nickel in charged state with the organic electrolyte, and the continuous growth of solid-electrolyte interphase (SEI) layer.3, 22,23 However, it is very difficult to achieve a uniform thin coating layer on each active particle, and the coating often reduces the energy density. Therefore, new concepts of structurally modified Ni-rich layered oxides offering high capacity,


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good cycling performance, and thermal stability were first introduced by Sun’s group.24 Following this, core-shell and concentration-gradient Ni-rich oxide materials have been comprehensively investigated by Sun’s group and others in last decade,5, 24-29 where the Ni-rich interior (core) delivers high capacity and the Mn-rich exterior (shell) provides a protection layer to improve the cyclability and thermal stability. In these materials, the electrochemically inactive Mn4+ can significantly improve the structural stability during cycling.12, 21, 30 However, as for concentration-gradient structural precursor, the co-precipitation condition is relatively difficult to control to obtain desired composition and particle size. On other hand, due to a different shrinkage ratio between the core and the shell after sufficient cycling, the structural mismatch at the interface will lead server capacity decay in core/single-shell structured cathodes.24, 26, 31, 32 In this work, a concentration-gradient (CG) Ni-rich layered oxide with an average composition of LiNi0.76Co0.1Mn0.14O2 is designed by lithiating a core/double-shell [Ni0.9Co0.1]0.4[Ni0.7Co0.1Mn0.2]0.5[Ni0.5Co0.1Mn0.4]0.1(OH)2 hydroxide precursor at high temperatures. The concentrationgradient structure could minimize to the structural mismatch and the difference in volume change between the core and the thick concentration-gradient shells. This material would have the advantages of concentration-gradient structures to enhance the cyclability. It exhibits excellent electrochemical performance in both coin-type half cells and pouch-type full cells. 2. EXPERIMENTAL SECTION Synthesis of Ni-rich layered oxides: The concentration-gradient Ni-rich oxides with an average composition of LiNi0.76Co0.1Mn0.14O2 was synthesized by a three-step co-precipitation process, followed by a lithiation process.5, 11 First, a 1.0 M aqueous solution with NiSO4∙6H2O and CoSO4∙7H2O was prepared and used for the preparation of the first-step precursor (Ni0.9Co0.1(OH)2). The prepared aqueous solution was continuously pumped into a stirred tank



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reactor. Simultaneously, a 2.0 M aqueous KOH solution with certain amount of NH3∙H2O was pumped into the reactor to control the pH value. The amount of NH3∙H2O was determined by the concentration of metal ions with a mole ratio of 1 : 1. The concentration of the metal solution (1 mol L-1), pH (11.0-11.3), temperature (50 oC), and stirring speed (1000 rpm) in the tank reactor was carefully controlled. All co-precipitation processes were operated under nitrogen atmosphere. The pH value controlled with aqueous KOH varied from 11.0 to 11.3 depending on the different metal-ion compositions. Second, a new metal sulfate (NiSO4∙6H2O, CoSO4∙7H2O, and MnSO4∙H2O) aqueous solution with a cationic ratio of Ni : Co : Mn = 7 : 1 : 2 was further pumped into the tank reactor to obtain the first shell (Ni0.7Co0.1Mn0.2(OH)2) on the Ni0.9Co0.1(OH)2

core,

forming

the

second-step

core/shell

precursor

((Ni0.9Co0.1)0.44(Ni0.7Co0.1Mn0.2)0.56(OH)2). Third, the precursor from step 2 was further reacted with the third solution containing NiSO4∙6H2O, CoSO4∙7H2O, and MnSO4∙H2O (cationic ratio of Ni : Co : Mn = 5 : 1 : 4) to have the final core/double-shell precursor [Ni0.9Co0.1]0.4[Ni0.7Co0.1 Mn0.2]0.5[Ni0.5Co0.1Mn0.4]0.1(OH)2. After filtering and washing with deionized water, the coprecipitated precursor powder was put into an air-oven and dried at 100 °C overnight. In order to achieve the final concentration-gradient layered oxides, the dried core/double-shell precursor was well mixed with 2 wt.% excess LiOH∙H2O (Li : M = 1.02 : 1) to compensate for any volatilization of Li during the heat treatment at 750 °C for 20 h in a flowing oxygen atmosphere. For a comparison, a constant-concentration LiNi0.76Co0.1Mn0.14OH2 was also prepared via a onestep co-precipitation process followed by lithiation, with all other experimental conditions same as that for the gradient sample. Structural Characterization: The morphologies of the Ni-rich hydroxide precursors and the layered oxides were characterized with a FEI Quanta 650 scanning electron microscope (SEM).


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The elemental distribution of Ni, Co, and Mn in prepared oxides and cycled oxides was analyzed by energy dispersive X-ray spectroscopy (EDS). The crystal structure and phase purity of the synthesized oxides were examined with an X-ray diffraction (XRD, Rigaku Miniflex 600) system with Cu K radiation from 10 to 80°. The XRD data were joint-refined by the conventional Rietveld method using the General Structure Analysis System (GSAS) package with the graphical user interface (EXPGUI).33 The average chemical compositions of the hydroxide precursor at each step and the layered oxides were measured with a Varian 715-ES inductively coupled plasma-atomic emission spectrometer (ICP-AES). Electrochemical Evaluation: The cathodes for low-loading electrodes were prepared by mixing the layered oxide (80 wt.%), Super P (10 wt.%), and PVDF binder (10 wt.%) in a Nmethylpyrrolidone (NMP) solution. The composition ratio for the high-loading cathodes was adjusted to 90: 5: 5. After casting the well-mixed slurry onto an aluminium foil, the obtained film was transferred into a vacuum oven at 110 oC overnight.5 CR2032 type coin cells consisting of a layered oxide cathode, a metallic lithium anode, and a Celgard separator were assembled in an argon-filled glovebox. 1.2 M LiPF6 in ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (3/7 by volume) mixture containing 2 wt.% vinylene carbonate (VC) was used as the electrolyte. For both the coin and pouch-type full cell tests, graphite was used for the anode. The negative and positive electrode capacity ratio for the full cell (N/P ratio) were in the range of 0.95 to 1.1. The electrode area of the coin-type full cell was 1.13 cm2 and the pouch-type full cell was 40 cm2. The punch-cells were fabricated by a MTI company set-up including aluminum laminated film (EQ-alf-400), aluminum tab as positive terminal, nickel tab as Negative Terminal, compact vacuum (MSK-115A-110V), semi-automatic die cutter (MSK-180), desk-top 800W Ultrasonic metal welder (40KHz - MSK-800W-110V), compact heating sealer (MSK-140-110V),



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etc. Galvanostatic cycling was conducted with an Arbin battery cycler at 2.7 – 4.5 V (vs. Li/Li+) at room temperature for half cells and at 2.5 – 4.4 V (vs. Li/Li+) for full cells. Galvanostatic cycling for half-cell was performed at C/10 rate for formation and C/3 rate for cycling, where 1C was defined as 200 mA g-1. 3. RESULTS AND DISCUSSION Figure S1 shows the scanning electron microscope (SEM) images of the hydroxide precursors prepared at different steps. Step I: Ni0.9Co0.1(OH)2; Step II: [Ni0.9Co0.1]0.44[Ni0.7Co0.1Mn0.2]0.56(OH)2;

Step

III:

[Ni0.9Co0.1]0.4[Ni0.7Co0.1Mn0.2]0.5[Ni0.5Co0.1Mn0.4]0.1(OH)2.

The

composition of the samples in each step was carefully controlled by inductively coupled plasmaatomic emission spectrometer (ICP-AES) measurement. It is obvious that all the prepared precursors at different steps show uniformly spherical morphology, assembled with needle-like primary particles, and the average secondary particle size increases from around 8 m to 11 m to 12 m from Step I (Figure S1a, supporting information) to Step II (Figure S1b) to Step III (Figure S1c, d). The as-synthesized core/double-shell hydroxide (Step III) was then well mixed with a required amount of lithium hydroxide and fired at 750 oC for 20 h in a flowing oxygen atmosphere to obtain the final concentration-gradient (CG) sample with an average composition of LiNi0.76Co0.1Mn0.14O2.


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Figure 1. (a-c) SEM images of the concentration-gradient (CG) samples and (d) EDS line scan: Ni/Co/Mn content distributions across the CG particle. (e, f) SEM images of the constantconcentration (CC) sample. The SEM images of the final CG sample shown in Figure 1 indicate a uniform spherical morphology as well, with an average secondary particle size of around 12 m (Figure 1a and b). As has already been suggested in the literature, the needle-like primary particles of the hydroxide precursor (Figure S1) changed into rod-like particles after the high temperature lithiation process, which is revealed by the cross section image of the CG sample (Figure 1c). In order to determine the compositional distribution in the CG particles, energy dispersive X-ray



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spectroscopy (EDS) was used to detect the element contribution in the cross-section of a single CG particle. As shown in Figure 1d, the line scan profiles clearly indicate that the atomic percentage of cobalt content remains constant at around 10% in the CG particle, while the nickel content decreases and manganese content increases gradually from the interior towards the outer layer of the particle. This indicates the formation of a concentration-gradient structure with increasing Mn concentration and decreasing Ni concentration from interior to exterior. Although the

three-step

co-precipitation

process

was

applied

for

the

core/double-shell

[Ni0.9Co0.1]0.4[Ni0.7Co0.1 Mn0.2]0.5[Ni0.5Co0.1Mn0.4]0.1(OH)2 precursor, only a small content (0.2) of cations varies at each step and the cations could easily diffuse at the interface during the hightemperature treatment. So we presume there is no sudden cation concentration change at those two interfaces and the cation contents vary smoothly from the interior to the exterior of the particle.11 For a comparison, a constant-concentration (CC) LiNi0.76Co0.1Mn0.14O2 sample was also synthesized through the same process by firing a mixture of constant-concentration Ni0.76Co0.1Mn0.14(OH)2 and LiOH. The SEM images of the lithiated CC sample shown in Figure 1e and 1f indicate a spherical morphology and a secondary particle size (12 m) similar to those of the CG sample. The average chemical composition of the CC and CG samples measured by ICP are, respectively, Li1.01Ni0.759Co0.101Mn0.14O2 and Li1.01Ni0.761-Co0.098Mn0.141O2, which are in good consistency with the designed compositions. The tap densities of both the CC and CG samples are around 2.3 g cm-3. The XRD patterns of the prepared CG and CC samples are presented in Figure 2a, and Figure 2b shows the refinement results of the CG sample. The XRD patterns (Figure 2a) clearly indicate that the synthesized CC and CG samples are both phasepure structures , and all observed peaks could be indexed to the layered hexagonal structure of α-NaFeO2(R-3m).34 The obvious splitting


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between the two adjacent peaks of (006)/(102) and (018)/(110) also indicates a typical layered structure for both CC and CG samples.3,4 Rietveld refinement was further carried out to obtain the cation disorder degree between Li+ and Ni2+ in CG sample (Figure 2b). The degree of cation disorder between Ni and Li was calculated to be around 3.5%, revealing not a serious cation disorder in CG sample.

Figure 2. (a) XRD patterns of the prepared layered oxide samples and (b) Rietveld refinement results of the CG XRD data. The electrochemical performances of the layered oxide cathodes were first evaluated in half cells. To compare the structural stability between the CC and CG samples during cycling, charge-discharge profiles at C/3 rate in the potential range of 2.7 to 4.5 V from the 1st to 200th cycles are shown in Figure 3a. The CC and CG samples indicate similar initial columbic efficiency of 82% and 81%, and deliver first-cycle discharge capacities of 195 and 185 mA h g-1, respectively. The higher initial discharge capacity of the CC sample could be ascribed to the higher Ni content on the exterior of the CC sample and higher Mn content on the exterior of the CG sample. The higher Mn content on the exterior could slow down Li+ diffusion during initial



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cycling. So the specific capacity of the CG sample increases continuously until 30 cycles. As shown in Figure3a and 3b, the CG sample presents superior Li+ intercalation stability at room temperature. After 200 cycles, a discharge capacity of 180 mA h g-1 is maintained with the concentration-gradient LiNi0.76Co0.1Mn0.14O2 sample (Figure 3b). In contrast, the constantconcentration LiNi0.76Co0.1Mn0.14O2 sample suffers from severe capacity fade and shows a low discharge capacity of 132 mA h g-1 over the same cycling period. Furthermore, the CG electrode shows lower polarization loss and voltage decline during cycling compared to the CC sample. As high cutoff voltages are known to cause severe side reactions between unstable tetravalent nickel ions with the organic electrolyte, the thicker SEI layer formed rapidly increases the kinetic barrier for Li+ diffusion and the capacity fade. In addition, the high Ni-content surface is unstable in the highly delithiated state and decomposes exothermally at ambient temperatures, releasing oxygen from the host structure and resulting in structural instability during cycling.3, 35, 36


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Figure 3. (a) Chare-discharge curves of low-loading CC and CG electrodes at C/3 rate between 2.7 and 4.5 V. (b) Cyclability comparison of the CC and CG electrodes at room temperature. First three charge-discharge curves of the high-loading CG electrode at (c) C/3 and (d) 1C rates, and (e) their cycling performance up to 100 cycles. (f) Effect of storage in air on the capacity and cycling performance of low-loading and high-loading CG electrodes.

The electrodes discussed above in Figure3a and 3b are low-loading electrodes, which are around 1 mA h cm-2 (4–5 mg cm-2). This loading is low for commercial cells, especially for portable and EV applications. Therefore, we increased our electrode loading up to 3–4 mA h cm11 ACS Paragon Plus Environment


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(15–20 mg cm-2). The charge-discharge curves based on the high-loading CG electrodes at C/3

and 1C rates are shown, respectively, in Figure 3c and Figure 3d. The initial discharge area capacity at C/3 rate reaches as high as 3.3 mA h cm-2, and the electrode at 1C gives an area capacity of 2.9 mA h cm-2 at first cycle. It is also noted that the 2nd and 3rd cycles nearly overlap with the first cycle, indicating good cycling performance for the high-loading electrodes as well. The cycling performances of these two electrodes, respectively, at C/3 and 1C rates in the voltage range of 2.7 − 4.5 V are shown in Figure3e. After operating the high-loading CG electrodes at C/3 and 1C for 100 cycles, the discharge capacities are still maintained, respectively, at 197 and 181 mA h g-1, corresponding to 99% and 100% of the 1st discharge capacity. Another issue for the Ni-rich layered oxides is that they are not stable in air, and they react with moisture and carbon dioxide to produce a large amount of residual lithium compounds like LiOH and Li2CO3.37 The presence of these lithium-compound residues is not desirable as they can lead to the release of gas during operation at high voltages and degrade the cyclability and rate capability.38 The effect of air-storage on the cyclability of the low- and high-loading CG electrodes was also examined as shown in Figure3f. The air-stored electrodes were obtained by exposing the freshly prepared electrodes to air for 6 months at room temperature. For the lowloading electrode, the initial discharge capacity dropped severely from 184 mA h g-1 for the fresh electrode to 130 mA h g-1 for stored electrode. Also, for the low-loading electrode, the capacity of the air-stored electrode decreased to 115 mA h g-1 after 20 cycles (88% capacity retention), while that of the fresh electrode maintained almost 100% capacity retention after 100 cycles. The high-loading electrode also encountered a drop in initial capacity and a decline in capacity retention after storing in air, but the drops in capacity (198 vs. 184 mA h g-1) and capacity


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retention (99% vs. 93%) are smaller than those of the low-loading electrodes. This indicates that the high-loading CG electrodes are more stable than the low-loading CG electrodes in air. This is because with a high-loading electrode, mainly the top surface undergoes reaction with moisture and CO2 in air to produce the lithium-compound residues, while with the low-loading electrode, a larger fraction of the electrode would undergo reaction with moisture and CO2. The morphological and structural evolutions of the high-loading CG electrode after 100 charge/discharge cycles are shown in Figure S2 and Figure 4. As shown in Figure S2, the surface structure and spherical morphology are maintained after 100 cycles (Figure 1). Figure 4a and 4b show the cross section of cycled the high-loading electrode at different magnifications. The thickness of the high-loading electrode is around 100 m (Figure 4a), and the CG particles are still densely compacted with carbon black and binder (Figure 4b). In order to confirm the gradient structure for the cycled particles, EDS was further applied on the cycled particle as shown in Figure 4c. The elemental intensity ratio of Mn/Ni across the cycled CG particle gradually increases from the interior to the exterior, showing that the gradient structure with increasing Mn and decreasing Ni from the interior to the exterior can also be maintained after cycling. The cycled CG electrode was further examined by XRD (Figure 4d), and the XRD pattern indicates that the cycled CG sample maintains the layered structure with an unchanged intensity ratio between the (003) and (104) reflections and a clear splitting of the (006) and (012) peaks and the (018) and (110) peaks.



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Figure 4. (a, b) SEM images of the cross section of the cycled CG electrode after 200 cycles at different magnifications. (c) Elemental intensity ratio of Mn/Ni across the cycled CG particle based on the EDS line-scanning data. (d) XRD patterns of the pristine sample powder and the cycled CG electrode. In order to assess the real characteristics of cathode materials, it is essential to evaluate the electrochemical performances in a full cell with a graphite anode. In the case of full-cell fabrication, calculation of the negative and positive electrode capacity ratio (N/P ratio) is important. Figure S3 and S3b show the first two charge/discharge curves of the coin-type full cells with two different negative to positive (N/P) ratios (0.95 and 1.05). All cells were charged to 4.4 V and discharged to 2.5 V at C/10 rate for formation and C/3 rate for cycling. Comparing these two cells, we confirm that the optimized N/P ratio for the full cell is 1.05, which has higher 14 ACS Paragon Plus Environment

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areal capacity and Coulombic efficiency at first cycle than that with a lower N/P ratio. As we expected, the optimized full cell with an N/P ratio of 1.05 shows excellent, stable cyclability during 250 cycles (94.1% retention). Meanwhile, the discharge capacity of the full cell with a lower N/P ratio of 0.95 continuously increased during the initial 50 cycles and after that decreased rapidly. From these electrochemical results, we could conclude that optimization of the full cell fabrication is critical to achieve good performance. After optimizing the N/P ratio and fabrication of the coin-type full cell, we also made pouch-type full cells. The electrode for the pouch-type full cell had 5 cm width and 8 cm length, which could have 35 times higher areal capacity than the electrode for the coin-type full cell. As shown in Figure 5a, the pouch-type full cell shows a capacity of 22.1 mA h (180 mA h g-1) at C/10 rate. The test condition for the pouchtype full cell was the same as that for the coin-type full cell. After the formation cycles, the longterm cycling performances of the pouch-type full cell was further measured during 500 cycles at C/3 rate (Figure 5b). As seen, this cell exhibits excellent cycle retention of 89% for 500 cycles (19.6 mA h) with almost 100% Coulombic efficiency. We believe this remarkable cycle performance is promising for applications that require high energy density and long cycle life, such as electric vehicles.



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Figure 5. (a) Charge-discharge profiles of pouch-type full cell fabricated with the CG cathode and graphite anode and (b) its cycling performance between 2.5 V and 4.4 V at C/3 rate

4. CONCLUSIONS In summary, a novel concentration-gradient Ni-rich layered oxide with an average composition of LiNi0.76Co0.1Mn0.14O2 has been obtained by firing a core/double-shell [Ni0.9Co0.1]0.4[Ni0.7Co0.1 Mn0.2]0.5[Ni0.5Co0.1Mn0.4]0.1(OH)2 hydroxide precursor with LiOH∙H2O at high temperatures. The nickel content decreases gradually and the manganese content increases linearly from the center to surface of each gradient sample particle. Compared to a constant-concentration sample, the


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gradient sample exhibits higher reversible capacity with superior cycling properties due to the higher content of inactive tetravalent Mn on the surface to suppress the reaction with the electrolyte. With high-loading electrodes, the CG sample delivers 3.3 mA h cm-2 with 99% retention after 100 cycles. The material morphology and phase and gradient structure also could be maintained after cycling. To verify the real characteristic of the prepared CG materials, pouch-type full cells with a graphite anode were examined as well. After 500 cycles at C/3 rate, the pouch cell delivered a high capacity of 19.6 mA h with 89% of the initial capacity. The results demonstrate the advantages of the concentration-gradient or core-shell structures, and we believe the good cycle performance of the Ni-rich layered oxides cathodes presented here make them attractive for next-generation lithium-ion batteries.

ASSOCIATED CONTENT Supporting Information SEM images of the hydroxides precursor at different steps and the cycled CG electrode after 100 cycles at C/3 rate. Charge-discharge profiles with different N/P ratios of the full cells. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *Tel: +1-512-471-1791. Fax: +1-512-471-7681. E-mail: [email protected]



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Author Contributions The manuscript was written through the contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-EE0006447. The authors appreciate Wangda Li for his helpful suggestions in the experimental design.

REFERENCES (1) Liu, Z. L.; Yu, A. S.; Lee, J. Y., Synthesis and Characterization of LiNi1-x-yCoxMnyO2 as the Cathode Materials of Secondary Lithium Batteries. J. Power Sources 1999, 81, 416-419. (2) Yoshio, M.; Noguchi, H.; Itoh, J.; Okada, M.; Mouri, T., Preparation and Properties of LiCoyMnxNi1-x-yO2 as a Cathode for Lithium Ion Batteries. J. Power Sources 2000, 90 (2), 176181. (3) Manthiram, A.; Knight, J. C.; Myung, S. T.; Oh, S. M.; Sun, Y. K., Nickel-Rich and Lithium-Rich Layered Oxide Cathodes: Progress and Perspectives. Adv. Energy Mater. 2016, 6 (1) DOI: 10.1002/aenm.201501010.


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(4) Zheng, J. M.; Kan, W. H.; Manthiram, A., Role of Mn Content on the Electrochemical Properties of Nickel-Rich Layered LiNi0.8-xCo0.1Mn0.1+xO2 (0.0

Double-Shell Type Gradient Ni-Rich LiNi0.76Co0.10Mn0.14O2

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