리튬이온배터리용 니켈리치 양극재료의 Sn 치환에 따른 구조적 전기화학적 영향

강가희 세종대학교 2017 국내석사

니켈 함량이 높은 3성분계 전이금속(Ni, Co, Mn)산화물은 고용량 구현을 위해 개발되었다. 하지만 Ni 함량이 증가함에 따라 구조적 안정성이 악화되는 단점이 있어 이를 개선하기 위하여 양극소재에 이종원소를 치환하는 연구가 활발히 진행되고 있다. 본 연구에서는 양극재료 개발에 있어 공침법을 통한 전구체 제조단계 이후에 Sn을 도핑하여 Li[Ni0.82Co0.12Mn0.06]1-xSnxO2(X = 0.004, 0.008, 0.012, 0.024)을 합성하였다. scanning electron microscopy(SEM)을 통해 전구체, 양극재의 형상이 구형임을 확인하였으며 energy-dispersive x-ray spectroscopy(EDS), cross-section polisher(CP)를 통해 Sn이 양극재 내부까지 치환되어 있음을 확인하였다. x-ray diffraction(XRD)를 통해 Sn이 치환됨에 따른 (003)피크의 저각으로의 이동으로 구조변화가 일어났음을 확인할 수 있었다. 또한 x-ray photoelectron spectroscopy(XPS)의 결과로 양극재의 구성원소 Ni은 2+, 3+로, Co는 3+로, Mn은 4+로, Sn은 4+로 존재함을 알 수 있었으며, Sn이 치환됨에 따른 각 원소들의 화학적 결합상태를 확인하였다. 입자강도 분석을 통해서 Sn이 치환됨에 따라 입자강도가 증가함을 보이다가 Sn 1.5wt%에서부터 감소함을 보이며 이는 Sn 1.5wt%부터 구조가 붕괴됨을 나타낸다. Sn 치환을 한 Li[Ni0.82Co0.12Mn0.06]1-xSnxO2의 전기화학적 특성인 수명특성과 출력특성이 Sn을 치환 하지 않은 Li[Ni0.82Co0.12Mn0.06]O2 보다 구조적인 안정성 향상 뿐만 아니라 수명특성, 출력특성을 향상시킴을 나타낸다. 하지만 Sn 1.5wt%부터 구조붕괴로 인해 불안정한 전기화학적 특성을 보이고 있다.

(The) effects of Fe as impurity element for sustainable resynthesis of Li[Ni1-x-yCoxMny]O2 cathode materials from spent lithium-ion batteries

박상혁 세종대학교 대학원 2019 국내박사

The electric vehicle market including hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV), and electric vehicle (EV), as one of major field of lithium-ion rechargeable battery (LIB) applications has been growing rapidly over the recent years. Accordingly, the overall volume of LIB production has been also skyrocketing and this is mainly resulting from the future direction of global automobile industry in domestic and overseas that is moving toward eco-friendly electric car systems due to strict regulations of worldwide environment concern. Thereby, the demand in raw materials consisting of rechargeable batteries which are a core part of EV is also expected to surge. Therefore, given the finite nature of resources that comprises battery material and the maldistribution of countries for production of the raw materials, recycling spent LIBs is mandatory as a countermeasure for not only procuring the raw materials but also preventing the potential environment threat in the coming years. With the raid development of EV market, the trend shifting especially in LIB cathode material was made from the conventional LiCoO2 (LCO) to nickel-based transition metal oxide materials such as Li[Ni1-x-yCoxMny]O2 (NCM), which is accelerated by the needs of higher energy density to satisfy more larger driving range. As a result, the existing LCO recycling process focusing on recovering mainly Li and Co simply by pyrometallurgical manner no longer effective in the case of NCM because of the difficulty in recovering Ni, Co, and Mn separately, thus leading to increase in additional purification costs. Meanwhile, the coprecipitating property of Ni, Co, and Mn in similar pH range in turn results in emerging the resynthesis process which is the concept of regeneration of cathode materials directly from leach liquor via coprecipitation method. However, the leach liquor treated by acid leaching process contains various impurity elements such as Li, Al, Cu, Fe, Na, Ca, Mg, etc. that significantly affect the electrochemical and structural properties of the resynthesized cathode materials. Therefore, dedicated efforts of investigating the impact of impurities in the resynthesized NCM on their LIB performance are necessary to determine the tolerable level of them from the aspects of industrial merit and material synthesis without any degradation of performance, respectively. In an attempt to establish a lab-scale sustainable resynthesis process of NCM cathode active material from spent LIBs, an intensive research focusing on the effect of Fe as an omnipresent impurity element in NCM cathode material was systematically dealt with in this dissertation. Firstly, we synthesize Li[Ni1/3Co1/3Mn1/3]O2 (NCM) and Li[Ni1/3Co1/3Mn1/3]FexO2 (NCMF) cathode active materials with various amounts of Fe via hydroxide coprecipitation and calcination processes, which simulate the resynthesis of NCM in leach liquor containing Fe from spent lithium ion batteries (LIBs). The crystal structure and electrochemical performances of the synthesized NCMF (i.e., NCMF (0.05%), NCMF (0.25%) and NCMF (1.0%)), are investigated and compared with pristine NCM. The structural perfection of NCMF gradually deteriorates with increasing the amount of Fe because of undesirable cation mixing between Ni2+/Fe3+ and Li+ sites. In LIB performances, NCMF (0.05%) and NCMF (0.25%) present relatively reduced overpotential leading to superior rate performance at high C-rates to NCM with NCMF (1.0%) having the poorest. In terms of cycling stability, however, capacity retention improves as the Fe content in NCMF increases. The thermal stability of NCM and NCMF is also measured by differential scanning calorimetry, and the post-mortem analysis of X-ray photoelectron spectroscopy reveals that the ratio of Mn3+ becomes lower after cycling tests as the amount of Fe in NCMF increases. Moreover, the additional post-mortem analysis of energy dispersive spectroscopy on graphite surface after full cell cycling tests further confirms the positive effect of Fe on the improved capacity retention performance of NCMF. Secondly, we synthesize trace amount of extra Fe (0.25%) incorporated Ni-rich NCM cathode material, Li0.97[Ni0.78Co0.12Mn0.10]Fe0.0023O2 (HNCMF), to develop the industrially feasible Ni-rich layered oxide cathode with improved electrochemical performance, especially rate capability. By exploiting the positive effects of Fe on the improved electrochemical property which is validated in NCM333 system, the modified structure of HNCMF significantly outperforms analogous bare material Li1.02[Ni0.78Co0.12Mn0.10]O2 (HNCMb). HNCMF shows lithium-deficient composition but reduced cation mixing ratio and the increase in initial Coulombic efficiency and charge/discharge capacity compared to HNCMb, notwithstanding the undesired nature of Fe3+ ions causing severe cation disordering between Ni2+/Fe3+ and Li+ sites detrimental to reversible capacity and rate performance. The advantage of the increased charge/discharge capacity and Coulombic efficiency of HNCMF is maintained at even in the 10 C-rate condition and it is noted that the discharge capacities at 1 C and 2 C for HNCMF are 163.73 mAh/g and 153.20 mAh/g, which are comparable as the values for HNCMb at 0.5 C (163.82 mAh/g) and 1C (153.90 mAh/g), respectively. Based on relatively lowered overpotentials, the improved structural and electrochemical property of HNCMF are scrutinized by conducting the analyses of in-situ X-ray diffraction and post-mortem high angle annular dark field scanning transmission electron microscopy.

Re-synthesis of lithium ion battery cathode active materials

구희숙 세종대학교 대학원 2016 국내석사

As the production and consumption of lithium ion batteries (LIBs) increase, the recycling of spent LIBs appears inevitable from an environmental, economic and health viewpoint. The leaching behavior of valuable metals such as Ni, Mn, Co, Al and Cu is investigated with ammoniacal leaching agents (ammonia, ammonium carbonate, and ammonium sulfite) for spent cathode active materials, which are separated from a commercial LIB pack in hybrid electric vehicles. Ammonium sulfite as a reductant is necessary to enhance leaching kinetics particularly in the ammoniacal leaching of Ni and Co. Ammonium carbonate can act a pH buffer so that the pH of leaching solution changes little during leaching. Co and Cu can be fully leached out whereas Mn and Al are hardly leached and Ni shows a moderate leaching efficiency. It is confirmed that the cathode active materials are a composite of LiMn2O4, LiCoxMnyNizO2, Al2O3 and C while the leach residue is composed of LiNixMnyCozO2, LiMn2O4, Al2O3, MnCO3 and Mn oxides. Co recovery via the ammoniacal leaching is believed to gain a competitive edge on conventional acid leaching both by reducing the sodium hydroxide expense for increasing the pH of leaching solution and by removing the separation steps of Mn and Al. Further, LiNi1/3Co1/3Mn1/3O2 cathode active materials are synthesized by using hydroxide co-precipitation method in simulated leaching solutions. An optimization conditions (pH and reaction atmosphere) and an effect of extra Li ions in simulated leaching solutions are investigated. Precursors and the active materials show spherical morphology, and their particles size has a tendency to increase with decreasing pH value. The LiNi1/3Co1/3Mn1/3O2 active materials at pH 10.50 present a relatively narrow particle size distribution, high crystallization, and good cycling performance. The LiNi1/3Co1/3Mn1/3O2 active materials in N2 atmosphere show a narrow particle distribution, good layered structure compared to the active materials in air atmosphere. The electrochemical performance of active materials in N2 atmosphere exhibits good cycling performance at low and high temperatures and low charge transfer resistance compared to the cathode active materials in air atmosphere. The amount of Li ions in the precursors obtained from simulated leaching solutions appears insignificant after adequate washing of precursors. The precursors with Li have spherical morphology and almost identical particle sizes similar to those without Li. 전기자동차, 모바일 IT기기 등의 수요가 증가함에 따라 리튬이온전지의 생산 및 소비가 증가하여, 폐리튬이온전지의 재활용은 환경적, 경제적 관점에서 반드시 요구된다. 본 연구에서는 하이브리드 자동차용 폐리튬이온전지로부터 파/분쇄된 양극활물질을 대상으로 암모니아 침출제 (NH3, (NH4)2CO3, (NH4)2SO3)를 이용해 양극활물질 내의 유용금속 (Ni, Mn, Co, Al, Cu)의 침출거동을 조사하였다. 환원제 ((NH4)2SO3)는 Ni과 Co의 암모니아침출에서 침출속도를 증가시키기 위해 필수적이며, pH 완충제 ((NH4)2CO3)는 침출하는 동안 침출용액의 pH변화를 최소화하기 위해 필요하다. Co와 Cu는 대부분 침출된 반면, Mn과 Al은 거의 침출이 되지 않았으며, Ni은 30% 정도의 침출률을 확인하였다. 특히, Co 회수의 경우 Co 침전을 위하여 추가되는 염기성 용액의 양을 줄일 수 있고, 침출액 내의 Mn과 Al의 분리단계를 줄일 수 있기에 산침출보다 경제적으로 이점이 있다고 여겨진다. 침출용액으로부터 직접 양극활물질을 재합성하는 방법을 검토하기 위해 LiNi1/3Co1/3Mn1/3O2을 수산화공침법을 이용해 합성최적화 (pH, 반응분위기)를 수행하고, 침출용액에서 과량의 리튬이온의 영향에 대해 알아보았다. 전구체와 양극활물질은 pH가 감소함에 따라 입자크기가 증가하는 경향을 나타냈다. pH 10.50의 LiNi1/3Co1/3Mn1/3O2 양극활물질은 좁은 입자크기분포도, 높은 결정성, 좋은 수명특성을 보였다. 공기분위기와 비교하였을 때 N2 분위기의 양극활물질은 균일한 입자크기분포도, 고온과 저온에서 좋은 수명특성, 낮은 전하이동저항을 나타내었다. 과량의 리튬이온이 포함된 침출모사용액에서 제조된 전구체는 충분한 세척 후에 리튬이 거의 제거됨을 확인하였으며, 이 전구체는 리튬이온이 포함되지 않은 용액으로부터 제조된 전구체와 비슷한 구형의 입자와 입자크기를 갖고 있다.

리튬이온배터리 양극 재합성 시 잔존하는 알루미늄의 전기화학적 영향

김상준 세종대학교 대학원 2020 국내석사

기존 전지들에 비해 우수한 출력과 에너지 밀도를 가지는 리튬이온배터리는 이러한 이점들을 필요로 하는 전기자동차 및 각종 전자기기의 수요가 증가함에 따라, 그 처리 또한 중요한 과제가 되어왔다. 본 연구에서는 양극의 집전체로 가장 널리 쓰이는 Al이 재활용 과정에서 양극활물질에 포함될 가능성에 주목하였다. 수산화 공침과 열처리 과정을 통하여 Li[Ni1/3Mn1/3Co1/3]O2 (NMC)과 다양한 조성의 Al을 포함하는 Li[Ni1/3Mn1/3Co1/3]AlxO2 (NMCA) 양극활물질 (NMCA(0.05%), NMCA(0.25%), NMCA(1.00%), NMCA(2.00%))을 제조하여 미량의 Al이 NMC에 미치는 물리화학적, 열적, 전기화학적(초기 충·방전 용량, 출력 특성, 수명 특성) 특성을 알아보았다. NMCA내 Al 함량이 증가함에 따라 주사전자현미경을 통해 양극활물질 입자의 분포와 모양이 불규칙해지는 것을 확인하였다. 초기 충·방전 용량과 수명 특성은 악화되었다. 가장 많은 Al 조성의 NMCA(2.00%)의 경우는 수명 특성이 다른 NMCA보다 더 일찍이 급격하게 악화되었다. 반면, 출력 특성이 향상되는 것을 확인하고 이를 명확히 하기 위하여 전기화학 임피던스 분광법을 수행하였고, NMCA(2.00%)에서의 리튬이온 확산상수가 NMC보다 높은 것을 확인하였다.

Utilization of impurities in resynthesized Ni-rich Li[Ni1-x-yCoxMny]O2 (1-x-y≥0.6) cathode materials from leachate for the effective spent lithium-ion battery recycling process

고경빈 세종대학교 대학원 2023 국내석사

In the typical hydrometallurgy-based recycling process of spent Li-ion batteries (LIBs), excessive amounts of metallic and nonmetallic impurity ions are incorporated in leachate. These impurities are removed through a precipitation reaction using NaOH to recycle into a cathode material, which has same performance as the cathode of the BOL battery. Na ions are inevitably incorporated in leachate through a discharging process with salt solutions and a purification step for impurity removal. In this study, a facile Al3+ doping strategy is realized ranging from impurity level to usual doping levels for improving the LIB performance of Na-incorporated Li[Ni0.8Co0.1Mn0.1]O2 (N-NCM). We synthesize Na-incorporated hydroxide precursor via a coprecipitation reaction using a metal solution containing excess amounts of Na (12.6 mol%), simulating the resynthesis of NCM from purified leachate. The Na and Al co-doped NCM811 (NA-NCM) cathode materials are successfully synthesized by subsequent solid-state reactions with various concentrations of Al. The physicochemical and electrochemical properties of NA-NCM are systematically investigated, with N-NCM as a control sample. Notably, the trace amount of Al (0.05 mol%)-doped cathode material reveals the highest cyclability of 93.9% after 80 cycles at 1 C and more than six times higher discharge capacity (115 mAh g−1) at 20 C than N-NCM. Overall, the small amount of Al doping (0.05 and 2 mol%) makes the host structures stable and more favorable for Li+ diffusion, whereas the excessive Al (4 mol%) doping lead to the sluggish kinetics on rate capability due to thick Al2O3 film layers formed on the particle surface. This work suggests the rational design for upgrading the resynthesized Ni-rich NCM cathode materials for the sustainable recycling of spent LIBs. Based on the fact that the impurity ions could be used as a dopant, Ni-rich NCM cathode materials (Re622, Re811, and Re955) are resynthesized by the coprecipitation method and the solid-state reaction. The actual leachate was utilized for the synthesis of various Ni-rich hydroxide precursors without a purification process, and in the case of cobalt, the whole required cobalt ions for synthesis were replaced by the leachate. A cathode active material (Re622) with high leachate usage (72 mol % of transition metals) has heterogeneous secondary particles and poor electrochemical performance. In contrast, the resynthesized Re955 using leachate for 18% of the required transition metals has homogeneous spherical secondary particles like those of a pristine NCM955 sample and shows enhanced cyclability and rate capability compared to the pristine NCM955 sample. This study demonstrates that the electrochemical performance of the resynthesized Ni-rich cathode materials could be improved by utilizing the impurities without purification process.

Effects of the removal rate of impurity on the electrochemical properties of resynthesized Li[Ni1-x-yCoxMny]O2 cathode active materials from spent lithium-ion battery leachate

김우석 세종대학교 대학원 2023 국내석사

Various impurities such as Cu, Al, and Fe can be incorporated in the leachate of spent lithium-ion batteries (LIB) after a conventional acidic leaching process. Here, we synthesize Fe/Al co-modified Ni-rich Li[Ni1-x-yCoxMny]O2 (NCM) cathode materials via a coprecipitation reaction for Fe doping and the subsequent calcination process for additional Al doping. The purpose of this work is to seek a potential of utilizing the positive effects of impurity elements for improving the LIB performance of Ni-rich NCM. The physicochemical properties of cathode materials are compared by scanning electron microscopy, energy dispersive spectroscopy, inductively coupled plasma optical emission spectroscopy and X-ray diffraction analysis. Electrochemical analyses including galvanostatic intermittent titration technique, differential capacity curves from cycling data are systematically performed to assess the effects of the sequential doping processes. It is found that an Al doping content of 1% in Fe-doped NCM is optimal in terms of rate and cycle performances. This study also proposes a rational design for upgrading the resynthesized Ni-rich NCM cathode materials from the leachate of spent LIBs. In addition, resynthesized precursors from the actual leachate, purified precursors, and a control sample are synthesized via co-precipitation method. The structure and electrochemical properties of the resynthesized precursors and the corresponding cathode materials are examined.

리튬이온배터리 양극 재합성 시 잔존하는 구리의 전기화학적 영향

조민상 세종대학교 대학원 2018 국내석사

최근 리튬이온배터리의 사용량이 증가함에 따라 수명이 다한 리튬이온배터리의 폐기량 또한 증가하고 있으며, 이에 따라 폐리튬이온배터리의 재활용이 중요해지며 관련 연구들이 진행되고 있다. 본 연구에서는 폐리튬이온배터리 재활용 시 잔존하는 구리의 전기화학적 영향에 대해 연구하기 위하여 공침 반응을 통해 수산화물 전구체 Cux[Ni1/3Co1/3Mn1/3]1-x(OH)2를 합성하였으며 열처리 과정을 통해 LiCux[Ni1/3Co1/3Mn1/3]1-xO2 양극활물질을 합성하고 전지를 제작하여 전기화학 성능 평가를 수행하였다. X-선 회절 분석을 통하여 전구체에 구리가 함유되었을 때 결정 구조의 불완전성이 증가함을 확인하였다. 또한 격자 상수의 감소와 (003)과 (104) 피크의 넓이비의 감소로부터 전구체의 구리 함량이 증가함에 따라 Li/Ni 양이온 혼합(cation mixing)이 심화되는 것을 확인하였다. 3.0-4.3 V의 전압 구간에서 전기화학 성능 평가를 진행하여, 구리 함량이 증가함에 따라 초기 충·방전 용량, 출력 특성, 수명 특성 등의 전기화학 성능이 저하되는 경향을 확인하였다. 따라서 폐리튬이온배터리로부터 양극활물질을 재합성할 때 침출 용액에 잔존하는 구리를 제거하는 과정이 필요할 것으로 보인다. As the production and consumption of LIBs increase, the treatment or recycling of spent LIBs appears inevitable from environmental and economic point of view. In this work, LiCux[Ni1/3Co1/3Mn1/3]1-xO2 cathode active materials are synthesized from co-precipitated hydroxide precursors Cux[Ni1/3Co1/3Mn1/3]1-x(OH)2, and the effect of residual Cu in the precursors on the electrochemical properties of their corresponding cathode active materials is investigated. Four kinds of precursors that contain different amounts of Cu are selected depending on different conditions of the solution composition for the co-precipitation. It is confirmed that the introduction of Cu to the precursors reduces the degree of structural perfection by X-ray diffraction analysis. Undesirable Li/Ni cation mixing occurs with the increasing Cu content of the precursors, which is inferred from a decline in lattice parameters and the calculated intensity ratio of (003) and (104) peaks. In the voltage range of 3.0-4.3 V, the initial charge/discharge capacities, rate capability, and the cyclability of the cathode active materials are aggravated when Cu exists in the precursors. Therefore, it could be concluded that the removal process for Cu in a solution for co-precipitation of precursors is necessary in the resynthesis of cathode active materials from spent LIBs.

Electrochemical effects of transition metal (Fe, Al, and Zn) dopants in lithium-ion battery cathode active materials

정성덕 세종대학교 대학원 2022 국내석사

It is widely accepted that lithium-ion batteries (LIBs) are a suitable candidate for electric vehicles (EVs) due to their excellent electrochemical performance, which is related to their long cycling life and high energy density. Recently, as the amount of spent LIBs has increased dramatically due to the explosive growth of the EV market, the importance of recycling spent LIBs is also increasing. One of the typical processes for recycling spent LIBs is hydrometallurgy, which dissolves substances inside the batteries using acid to obtain leachate. Various impurities such as Fe, Al, Cu, Zn, and Ca are incorporated into the obtained leachate. Inspired by the fact that these impurities could affect electrochemical performance by being incorporated into regenerated LiNixCoyMnzO2 (NCM), the effects of Fe, Al, and Zn in the cathode active materials are confirmed in this study. The effects of major impurities (>50 ppm in the leachate) of Fe/Al and minor impurity (≤ 50 ppm in the leachate) of Zn are confirmed by synthesizing NCM in simulated leachate where the impurity content is controlled according to the actual leachate obtained in the industry. In the case of Zn-doped NCM, the effect on the substitution of Zn for Co is further investigated. This work not only elucidates the positive doping effect of impurities such as Fe, Al, and Zn in the regenerated cathode active materials but also further provides a practical approach to designing a Co-free Ni-rich cathode for higher energy density. 리튬이온 배터리는 고에너밀도 특성으로 전기자동차용 배터리에 적합한 후보라는 것이 널리 받아들여지고 있다. 최근, 전기자동차 시장의 폭발적인 성장에 따라 리튬이온 배터리의 사용량이 급격하게 증가하면서, 사용 후 배터리를 재활용하는 방안도 동시에 화제가 되고 있다. 사용된 배터리를 재활용하는 공정 중에는 대표적으로 습식방식이 있으며, 이는 산을 이용하여 배터리 내부의 물질을 녹임으로써 침출수의 형태를 얻게 된다. 얻어진 침출수에는 여러 가지 불순물이 유입되며, 대표적으로 철, 알루미늄, 구리와 미량의 아연, 칼슘 등이 포함되어 있다. 이러한 불순물들이 재생된 양극활물질에 유입되어 전기화학적 성능에 영향을 미칠 수 있다는 사실에 영감을 받아, 본 연구에서는 철, 알루미늄, 아연이 양극활물질에 미치는 영향을 파악한다. 침출수에 50 ppm 이상 존재하는 주요 불순물인 철/알루미늄과 침출수에 50 ppm 미만 존재하는 아연의 불순물 양만큼을 양극활물질에 각각 도핑하여 불순물에 대한 영향을 확인한다. 아연의 경우 불순물의 양에서뿐만 아니라 코발트를 아연으로 완전히 치환하는 수준까지 양극활물질에 도핑 하여 영향을 확인한다. 본 연구는 불순물만큼의 도핑 수준에 대한 긍정적인 도핑 효과를 설명할 뿐만 아니라, 코발트 대신 아연을 사용하여 양극활물질을 설계하는 실용적인 접근법을 제공한다.