• Title, Summary, Keyword: Ni-Rich Cathode

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Stabilization of Nickel-Rich Layered Cathode Materials of High Energy Density by Ca Doping (칼슘 도핑을 통한 고 에너지 밀도를 가지는 Ni-rich 층상 구조형 양극 소재의 안정화)

  • Kang, Beomhee;Hong, Soonhyun;Yoon, Hongkwan;Kim, Dojin;Kim, Chunjoong
    • Korean Journal of Materials Research
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    • v.28 no.5
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    • pp.273-278
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    • 2018
  • Lithium-ion batteries have been considered the most important devices to power mobile or small-sized devices due to their high energy density. $LixCoO_2$ has been studied as a cathode material for the Li-ion battery. However, the limitation of its capacity impedes the development of high capacity cathode materials with Ni, Mn, etc. in them. The substitution of Mn and Ni for Co leads to the formation of solid solution phase $LiNi_xMn_yCo_{1-x-y}O_2$ (NMC, both x and y < 1), which shows better battery performance than unsubstituted $LiCoO_2$. However, despite a high discharge capacity in the Ni-rich compound (Ni > 0.8 in the metal site), poor cycle retention capability still remains to be overcome. In this study, aiming to improve the stability of the physical and chemical bonding, we investigate the stabilization effect of Ca in the Ni-rich layered compound $Li(Ni_{0.83}Co_{0.12}Mn_{0.05})O_2$, and then Ca is added to the modified secondary particles to lower the degree of cationic mixing of the final particles. For the optimization of the final grains added with Ca, the Ca content (x = 0, 2.5, 5.0, 10.0 at.%) versus Li is analyzed.

Effect of Sulfate-based Cathode-Electrolyte Interphases on Electrochemical Performance of Ni-rich Cathode Material

  • Chae, Bum-Jin;Song, Hye Ji;Mun, Junyoung;Yim, Taeeun
    • Journal of Electrochemical Science and Technology
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    • v.11 no.4
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    • pp.361-367
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    • 2020
  • Recently, layered nickel-rich cathode materials (NCM) have attracted considerable attention as advanced alternative cathode materials for use in lithium-ion batteries (LIBs). However, their inferior surface stability that gives rise to rapid fading of cycling performance is a significant drawback. This paper proposes a simple and convenient coating method that improves the surface stability of NCM using sulfate-based solvents that create artificial cathode-electrolyte interphases (CEI) on the NCM surface. SOx-based artificial CEI layer is successfully coated on the surface of the NCM through a wet-coating process that uses dimethyl sulfone (DMS) and dimethyl sulfoxide (DMSO) as liquid precursors. It is found that the SOx-based artificial CEI layer is well developed on the surface of NCM with a thickness of a few nanometers, and it does not degrade the layered structure of NCM. In cycling performance tests, cells with DMS- or DMSO-modified NCM811 cathodes exhibited improved specific capacity retention at room temperature as well as at high temperature (DMS-NCM811: 99.4%, DMSO-NCM811: 88.6%, and NCM811: 78.4%), as the SOx-based artificial CEI layer effectively suppresses undesired surface reactions such as electrolyte decomposition.

Changes in the Shape and Properties of the Precursor of the Rich-Ni Cathode Materials by Ammonia Concentration (암모니아 농도에 따른 Rich-Ni 양극 소재의 전구체 형태와 특성 변화)

  • Park, Seonhye;Hong, Soonhyun;Jeon, Hyeonggwon;Kim, Chunjoong
    • Korean Journal of Materials Research
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    • v.30 no.11
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    • pp.636-640
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    • 2020
  • Due to the serious air pollution problem, interest in eco-friendly vehicles is increasing. Solving the problem of pollution will necessitate the securing of high energy storage technology for batteries, the driving force of eco-friendly vehicles. The reason for the continuing interest in the transition metal oxide LiMO2 as a cathode material with a layered structure is that lithium ions reveal high mobility in two-dimensional space. Therefore, it is important to investigate the effective intercalation and deintercalation pathways of Li+, which affect battery capacity, to understand the internal structure of the cathode particle and its effect on the electrochemical performance. In this study, for the cathode material, high nickel Ni0.8Co0.1Mn0.1(OH)2 precursor is synthesized by controlling the ammonia concentration. Thereafter, the shape of the primary particles of the precursor is investigated through SEM analysis; X-ray diffraction analysis is also performed. The electrochemical properties of LiNi0.8Co0.1Mn0.1O2 are evaluated after heat treatment.

Designing of a Novel Core-Shell-Structured Co-free Cathode Material with Enhanced Thermal and Structural Stability for Lithium Ion Batteries

  • Shin, Ji-Woong;Nam, Yun-Chae;Son, Jong-Tae
    • Journal of the Korean Electrochemical Society
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    • v.22 no.4
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    • pp.172-176
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    • 2019
  • The first commercialized cathode material, $LiCoO_2$, suffers from disadvantages such as high cost and toxicity and also possesses safety problems. The nickel-rich $LiNi_{0.9}Mn_{0.1}O_2$ cathode material, used as an alternative to $LiCoO_2$, has highly reversible capacity and high energy density. So, the nickel-rich $LiNi_{0.9}Mn_{0.1}O_2$ cathode material is widely used as an alternative to $LiCoO_2$ due to its highly reversible capacity and high energy density. However, $LiNi_{0.9}Mn_{0.1}O_2$ has several disadvantages as well, such as poor cycle performance and poor thermal instability. To address these problems, we synthesized a new material, $LiNi_{0.5}Mn_{0.5}O_2$, as a shell on the surface of a core to suppress the surface degradation. The new material showed high structural and thermal stabilities and could also maintain a high capacity. The capacity retention of the core-shell cathode (87.7%) was better than that of the core cathode (76.9%) after 50 cycles. Analysis using differential scanning calorimetry revealed that the heat generation in the core-shell cathode ($65.9Jg^{-1}$) was lower than that in the core cathode ($559.7Jg^{-1}$).

Silyl-group functionalized organic additive for high voltage Ni-rich cathode material

  • Jang, Seol Heui;Jung, Kwangeun;Yim, Taeeun
    • Current Applied Physics
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    • v.18 no.11
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    • pp.1345-1351
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    • 2018
  • To allow stable cycling of layered nickel-rich cathode material at high voltage, silyl-functionalized dimethoxydimethylsilane is proposed as a multi-functional additive. In contrast to typical functional additive, dimethoxydimethylsilane does not make artificial cathode-electrolyte interfaces by electrochemical oxidation because it is quite stable under anodic polarization. We find that dimethoxydimethylsilane mainly focuses on scavenging nucleophilic fluoride species that can be produced by electrolyte decomposition during cycling, leading to improving interfacial stability of both nickel-rich cathode and graphite anode. As a result, the cell cycled with dimethoxydimethylsilane-controlled electrolyte exhibits 65.7% of retention after 100 cycle, which is identified by systematic spectroscopic analyses for the cycled cell.

Selective doping of Li-rich layered oxide cathode materials for high-stability rechargeable Li-ion batteries

  • Han, Dongwook;Park, Kwangjin;Park, Jun-Ho;Yun, Dong-Jin;Son, You-Hwan
    • Journal of Industrial and Engineering Chemistry
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    • v.68
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    • pp.180-186
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    • 2018
  • We report the discovery of Li-rich $Li_{1+x}[(Ni_{0.225}Co_{0.15}Mn_{0.625})_{1-y}V_y]O_2$ as a cathode material for rechargeable lithium-ion batteries in which a small amount of tetravalent vanadium ($V^{4+}$) is selectively and completely incorporated into the manganese sites in the lattice structure. The unwanted oxidation of vanadium to form a $V_2O_5-like$ secondary phase during high-temperature crystallization is prevented by uniformly dispersing the vanadium ions in coprecipitated $[(Ni_{0.225}Co_{0.15}Mn_{0.625})_{1-y}V_y](OH)_2$ particles. Upon doping with $V^{4+}$ ions, the initial discharge capacity (>$275mA\;h\;g^{-1}$), capacity retention, and voltage decay characteristics of the Li-rich layered oxides are improved significantly in comparison with those of the conventional undoped counterpart.

Synthesis and Electrochemical Performance of Ni-rich NCM Cathode Materials for Lithium-Ion Batteries (리튬이온전지 양극활물질 Ni-rich NCM의 합성과 전기화학적 특성)

  • Kim, Soo Yeon;Choi, Seung-Hyun;Lee, Eun Joo;Kim, Jeom-Soo
    • Journal of the Korean Electrochemical Society
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    • v.20 no.4
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    • pp.67-74
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    • 2017
  • Layered Ni-rich NCM cathode materials $Li[Ni_xCo_{(1-x)/2}Mn_{(1-x)/2}]O_2$ ($x{\geq}0.6$) have advantages of high energy density and cost competitive over $LiCoO_2$. The discharge capacity of NCM increases proportionally to the Ni contents. However, there is a problem that it is difficult to realize the stable electrochemical performance due to cation mixing. In this study, synthesis conditions for the layered Ni-rich NCMs are investigated to achieve deliver the ones having good electrochemical performances. Synthesis parameters are atmosphere, lithium source, synthesis time, synthesis temperature and Li/M (M=transition metal) ratio. The degree of cation mixing gets worse as the Ni content is increased from $Li[Ni_{0.6}Co_{0.2}Mn_{0.2}]O_2$ (NCM6) to $Li[Ni_{0.8}Co_{0.1}Mn_{0.1}]O_2$ (NCM8). It is confirmed that higher level of cation mixing affects negatively on the electrochemical performance of NCMs. Optimum synthesis conditions are explored for NCMx (x=6, 7, 8) in order to reduce the cation mixing. Under optimized conditions for three representative NCMx, a high initial discharge capacity and a good cycle life are obtained for $180mAh{\cdot}g^{-1}$, 96.2% (50 cycle) in NCM6, $187mAh{\cdot}g^{-1}$, 94.7% (50 cycle) in NCM7, and $201mAh{\cdot}g^{-1}$, 92.7% (50 cycle) in NCM8, respectively.

Analysis for Atomic Structural Deterioration and Electrochemical Properties of Li-rich Cathode Materials for Lithium Ion Batteries (리튬이차전지용 리튬과잉계 양극 산화물의 충방전 과정 중 원자 구조 열화 과정과 전기화학 특성에 대한 분석)

  • Park, Seohyeon;Oh, Pilgun
    • Applied Chemistry for Engineering
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    • v.31 no.1
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    • pp.97-102
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    • 2020
  • Recently, various degradation mechanisms of lithium secondary battery cathode materials have been revealed. As a result, many studies on overcoming the limitation of cathode materials and realizing new electrochemical properties by controlling the degradation mechanism have been reported. Li-rich layered oxide is one of the most promising cathode materials due to its high reversible capacity. However, the utilization of Li-rich layered oxide has been restricted, because it undergoes a unique atomic structure change during the cycle, in turn resulting in unwanted electrochemical degradations. To understand an atomic structure deterioration mechanism and suggest a research direction of Li-rich layered oxide, we deeply evaluated the atomic structure of 0.4Li2MnO3_0.6LiNi1/3Co1/3Mn1/3O2 Li-rich layered oxide during electrochemical cycles, by using an atomic-resolution analysis tool. During a charge process, Li-rich materials undergo a cation migration of transition metal ions from transition metal slab to lithium slab due to the structural instability from lithium vacancies. As a result, the partial structural degradation leads to discharge voltage drop, which is the biggest drawback of Li-rich materials.

Improvement of Electrochemical Properties and Thermal Stability of a Ni-rich Cathode Material by Polypropylene Coating

  • Yoo, Gi-Won;Son, Jong-Tae
    • Journal of Electrochemical Science and Technology
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    • v.7 no.2
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    • pp.179-184
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    • 2016
  • The interface between the surface of a cathode material and the electrolyte gives rise to surface reactions such as solid electrolyte interface (SEI) and chemical side reactions. These reactions lead to increased surface resistance and charge transfer resistance. It is consequently necessary to improve the electrochemical characteristics by suppressing these reactions. In order to suppress unnecessary surface reactions, we coated cathode material using polypropylene (PP). The PP coating layer effectively reduced the SEI film that is generated after a 4.3 V initial charging process. By mitigating the formation of the SEI film, the PP-coated Li[(Ni0.6Co0.1Mn0.3)0.36(Ni0.80Co0.15Al0.05)0.64)]O2(NCS) electrode provided enhanced transport of Li+ ions due to reduced SEI resistance (RSEI) and charge transfer resistance (Rct). The initial charge and discharge efficiency of the PP-coated NCS electrode was 96.2 % at a current density of 17 mA/g in a voltage range of 3.0 ~ 4.3 V, whereas the efficiency of the NCS electrode was only 94.7 %. The presence of the protective PP layer on the cathode improved the thermal stability by reducing the generated heat, and this was confirmed via DSC analysis by an increased exothermic peak.

Effect of Tris(trimethylsilyl) Phosphate Additive on the Electrochemical Performance of Nickel-rich Cathode Materials at High Temperature

  • Jang, Seol Heui;Mun, Junyoung;Kang, Dong-Ku;Yim, Taeeun
    • Journal of Electrochemical Science and Technology
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    • v.8 no.2
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    • pp.162-168
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    • 2017
  • $LiNi_xCo_yMn_zO_2$ cathode materials have been the focus of much attention because of their high specific capacity. However, because of the poor interfacial stability between cathodes and electrolytes, the cycling performance of these materials fades rapidly, especially at high temperatures. In the present paper, we propose the use of tris(trimethylsilyl) phosphate (TMSPO), which contains phosphate and silyl functional groups, as a functional additive in electrolytes. The addition of TMSPO resulted in the formation of cathode electrolyte interphase (CEI) layers on the surfaces of the cathodes and effectively suppressed electrolyte decomposition reactions, even at high temperatures. As a result, cells cycled with TMSPO exhibited remarkable capacity, which remained after 50 cycles (82.0%), compared to cells cycled without TMSPO (64.6%).