New Insights into Improving Rate Performance of Lithium‐Rich Cathode Material

Wang, Yong Qing; Yang, Zhenzhong; Qian, Yumin; Gu, Lin; Zhou, Haoshen

doi:10.1002/adma.201500956

Cited by 189 publications

(159 citation statements)

References 43 publications

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“…have attracted wide attention because of their high specifi c capacity (up to 250 mA h g −1 ), low cost, and high safety. In recent years, much effort has been paid to surface stabilization, such as doping, [9][10][11][12] heterostructuring, [13][14][15] and coating, [16][17][18][19] to overcome these issues that plague their practical implementation. [ 6 ] The kinetics could become even worse for lithium-rich materials with large dense particles.…”

Section: Doi: 101002/aenm201501914mentioning

confidence: 99%

Enhancing the Kinetics of Li‐Rich Cathode Materials through the Pinning Effects of Gradient Surface Na⁺ Doping

Qing

Shi

Xiao

et al. 2015

Advanced Energy Materials

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324

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facilitate the electrochemical activity of Li 2 MnO 3 . [22][23][24] Conventional approaches in activating Li 2 MnO 3 component in Lirich layered materials are mainly through chemical etching of Li 2 O in Li 2 MnO 3 phases to generate structural defects, such as nitric acid or hydrazine hydrate modifi cation. [ 6,20,25 ] Although Li 2 MnO 3 could be activated, which improved the initial Coulombic effi ciency, the original surface morphology is prone to being destroyed during the etching process ( Figure S1a, Supporting Information), hence leading to the poor cycling stability ( Figure S1b, Supporting Information) and rate performance during subsequent cycles. Li-rich layered materials modifi ed by hydrazine hydrate was reported to have long-term energy retention. [ 20 ] However, the unfavorable platform below 3.0 V appears in the discharge process, which compromises the energy density, especially for the Mn-rich based Li-rich cathode materials ( Figure S2, Supporting Information).Xia and co-workers reported to improve their electrochemical performances through controlled structure defects in Li 2 MnO 3 phase of Li-rich materials. [ 26 ] However, a high degree of structure defects, accompanied with highly disordering of Li + in the transition metal layer, would deteriorate the structural stability, leading to the poor cycling stability and the rate capacity. Na + doping has been reported to be an effective avenue to facilitate the Li + diffusion of Li-rich layered materials and thus to improve their rate capacity. [27][28][29][30] Note that it is vital to control the doping amount of Na + . Li-rich layered materials doped with a low amount of Na + would exhibit the poor cycling stability whereas the material doped with a high amount of Na + shows decreased specifi c capacity and deteriorates the energy density. [ 28 ] Therefore, it is still challenging to develop one simple and effective approach to synthesize Li-rich layered material with much improved kinetics.Herein, we propose a novel method to enhance the kinetics of large particle Li-rich layered materials by gradient surface Na + doping. Driven by Na + concentration diffusion thermodynamically, gradient surface Na + doping are realized through the calcination process of Li-rich materials in molten NaCl state. Powder X-ray diffraction (XRD) shows that high degree of structure defects are formed in Li 2 MnO 3 phase of Li-rich material in molten NaCl fl ux. [ 26 ] Gradient Na + doping on the surface of large particle Li-rich layered material could not only realize the pinning effect in stabilizing the Li-rich layered structure with large amount of structural defects but also facilitate the diffusion of Li + in the layered structure. Accordingly, the resultant large particle Li-rich layered material represents superior electrochemical performances, particularly high specifi c capacity, excellent Coulombic effi ciency, and impressive cycling stability. The schematic illustration of the structural design is shown in Figure 1 .

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Section: Doi: 101002/aenm201501914mentioning

confidence: 99%

Enhancing the Kinetics of Li‐Rich Cathode Materials through the Pinning Effects of Gradient Surface Na⁺ Doping

Qing

Shi

Xiao

et al. 2015

Advanced Energy Materials

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324

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“…It has shown that the originally well integrated LiMO 2 and Li 2 MnO 3 layered structure slowly transforms to a nano-composite where spinel LiMn 2 O 4 -like regions are embedded in a layered LiMO 2 framework. [8][9][10][11][12][13] As a result, the average discharge voltage gradually decreases leading to reduction in the specific energy of the battery. Furthermore, continuous capacity fading is always observed as a result of Mn dissolution and Jahn-Teller distortion of the Mn 3+ ions.…”

Section: Introductionmentioning

confidence: 99%

High-Performance Li(Li_0.18Ni_0.15Co_0.15Mn_0.52)O₂@Li₄M₅O₁₂ Heterostructured Cathode Material Coated with a Lithium Borate Oxide Glass Layer

Bian

Qiu

et al. 2015

Chem. Mater.

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The continuous phase transformation to spinel LiMn 2 O 4 seriously hinders the electrochemical properties of Li-excess layered oxides in lithium ion batteries. Herein, we prepared a heterostructured Li-excess layered cathode material consisting of a Li(Li 0.18 Ni 0.15 Co 0.15 Mn 0.52 )O 2 active material in conjunction with a surface Li 4 M 5 O 12 spinel and a Li 2 O-LiBO 2 -Li 3 BO 3 glass coating layer. The material showed improved electrochemical kinetic properties with respect to its pristine counterpart because the Li 2 O-LiBO 2 -Li 3 BO 3 glass layer not only improved the ionic conductivity of the material but also depressed the side reactions of the electrode with the electrolyte. In addition, the surface Li 4 M 5 O 12 spinel constantly grew inwards the bulk of the material during long term charge-discharge cycling instead of the conventional LiMn 2 O 4 transformation for the pristine Li(Li 0.18 Ni 0.15 Co 0.15 Mn 0.52 )O 2 . As a result, the heterostructured cathode material showed overall improved electrochemicalperformance. An initial discharge capacity of 258.8 mAh g -1 was obtained at the 0.2 C rate with remarkable capacity retention of 92.2 % after 100 cycles. Moreover, the material showed excellent rate capacity delivering a high discharge capacity of 130.4 mAh g -1 and 100.4 mAh g -1 at the 10 C and 20 C rates, respectively. Differential scanning calorimetry showed that the exothermic temperature of the fully charged electrode was elevated to 324.2 o C with little thermal release of 232.5 J g -1 demonstrating good thermal safety of the material.

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“…[15][16][17][18] The origin of voltage/capacity decay upon cycling stems from cation migration between TM layers and Li layers and subsequent phase transformation. [19,20] The cationic doping with other metallic cations (such as Mg, [21] Al, [22] Ti, [23] Sn, [24] Ru, [25] Y, [26] Zn, [27] etc.) and polyanion doping based on nonmetal elements, such as BO 4 5− , [28] SiO 4 4− , [29] PO 4 3-, [30] etc., have been employed to improve the cyclic durability by weakening the TM-O covalency in the oxygen closepacked structure.…”

mentioning

confidence: 99%

Surface Structural Transition Induced by Gradient Polyanion‐Doping in Li‐Rich Layered Oxides: Implications for Enhanced Electrochemical Performance

Zhao

Liu

Wang

et al. 2016

Adv Funct Materials

162

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To meet the demanding requirements in plug-in hybrid electric vehicles (PHEVs) or electric vehicles (EVs), higher energy density materials, such as the Li-rich, layered manganese-based oxides (LLOs) with the general formula xLi 2 MnO 3 ·(1-x)LiTMO 2 (TM = Mn, Ni, Co, etc.), are promising candidates as they possess higher reversible capacity (>250 mAh g −1 ), improved safety and much reduced cost. [4][5][6][7][8][9] Recent microscopic evidence reveals the intergrowth of rhombohedral LiTMO 2 (R-3m) and the monoclinic Li 2 MnO 3 -like layered structure (C/2m) at the atomic scale in the oxide grains. [10] The Li 2 MnO 3 component serves as an electrochemically active phase for Li storage when cycled above 4.5 V versus Li/Li + . [8,[11][12][13][14] Nevertheless, these LLO materials undergo steady voltage/capacity decay when cycled above 4.5 V, resulting in a substantial decrease of the cathode energy density. [15][16][17][18] The origin of voltage/capacity decay upon cycling stems from cation migration between TM layers and Li layers and subsequent phase transformation. [19,20] The cationic doping with other metallic cations (such as Mg, [21] Al, [22] Ti, [23] Sn, [24] Ru, [25] Y, [26] Zn, [27] etc.) and polyanion doping based on nonmetal elements, such as BO 4 5− , [28] SiO 4 4− , [29] PO 4 3-, [30] etc., have been employed to improve the cyclic durability by weakening the TM-O covalency in the oxygen closepacked structure. In addition, surface coatings using metal oxides, [31][32][33][34] fluorides and phosphates, [35][36][37] LiNiPO 4 and Li 3 VO 4 , [38][39][40] have been applied to protect the surface structure from side reactions with the electrolyte under high voltage and to restrain the layered-to-spinel transformation which occurs preferentially on the crystal surface and leads to capacity fading of LLO materials. However, the ionic dopants and coating materials are mostly electrochemically inactive, so the improved cycling stability is achieved at the expense of reduced specific capacity/energy density of the cathode. Moreover, a conformal and continuous coating on the surface of oxide particles is rather difficult to obtain practically. Hence, advancing the structural and cycling stability in both the bulk material and the surface structure through a simple way is highly desired for potential applications of LLO materials.Herein, we develop a novel LLO material with a nanoscaled spinel-like surface layer through gradient doping of polyanions Surface Structural Transition Induced by Gradient Polyanion-Doping in Li-Rich Layered Oxides: Implications for Enhanced Electrochemical PerformanceYing Zhao, Jiatu Liu, Shuangbao Wang, Ran Ji, Qingbing Xia, Zhengping Ding, Weifeng Wei,* Yong Liu, Peng Wang,* and Douglas G. Ivey Lithium-rich layered oxides (LLOs) exhibit great potential as high-capacity cathode materials for lithium-ion batteries, but usually suffer from capacity/ voltage fade during electrochemical cycling. Herein, a gradient polyaniondoping strategy is developed to initiate surface structural trans...

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New Insights into Improving Rate Performance of Lithium‐Rich Cathode Material

Cited by 189 publications

References 43 publications

Enhancing the Kinetics of Li‐Rich Cathode Materials through the Pinning Effects of Gradient Surface Na⁺ Doping

Enhancing the Kinetics of Li‐Rich Cathode Materials through the Pinning Effects of Gradient Surface Na⁺ Doping

High-Performance Li(Li_0.18Ni_0.15Co_0.15Mn_0.52)O₂@Li₄M₅O₁₂ Heterostructured Cathode Material Coated with a Lithium Borate Oxide Glass Layer

Surface Structural Transition Induced by Gradient Polyanion‐Doping in Li‐Rich Layered Oxides: Implications for Enhanced Electrochemical Performance

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New Insights into Improving Rate Performance of Lithium‐Rich Cathode Material

Cited by 189 publications

References 43 publications

Enhancing the Kinetics of Li‐Rich Cathode Materials through the Pinning Effects of Gradient Surface Na+ Doping

Enhancing the Kinetics of Li‐Rich Cathode Materials through the Pinning Effects of Gradient Surface Na+ Doping

High-Performance Li(Li0.18Ni0.15Co0.15Mn0.52)O2@Li4M5O12 Heterostructured Cathode Material Coated with a Lithium Borate Oxide Glass Layer

Surface Structural Transition Induced by Gradient Polyanion‐Doping in Li‐Rich Layered Oxides: Implications for Enhanced Electrochemical Performance

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Enhancing the Kinetics of Li‐Rich Cathode Materials through the Pinning Effects of Gradient Surface Na⁺ Doping

Enhancing the Kinetics of Li‐Rich Cathode Materials through the Pinning Effects of Gradient Surface Na⁺ Doping

High-Performance Li(Li_0.18Ni_0.15Co_0.15Mn_0.52)O₂@Li₄M₅O₁₂ Heterostructured Cathode Material Coated with a Lithium Borate Oxide Glass Layer