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First-principles study of effects of Ga, Ge and As doping on electrochemical properties and electronic structure of Li2CoSiO4 serving as cathode material for Li-ion batteries

Yan Xiao-Tong Hou Yu-Hua Zheng Shou-Hong Huang You-Lin Tao Xiao-Ma

Yan Xiao-Tong, Hou Yu-Hua, Zheng Shou-Hong, Huang You-Lin, Tao Xiao-Ma. First-principles study of effects of Ga, Ge and As doping on electrochemical properties and electronic structure of Li2CoSiO4 serving as cathode material for Li-ion batteries. Acta Phys. Sin., 2019, 68(18): 187101. doi: 10.7498/aps.68.20190503
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First-principles study of effects of Ga, Ge and As doping on electrochemical properties and electronic structure of Li2CoSiO4 serving as cathode material for Li-ion batteries

Yan Xiao-Tong, Hou Yu-Hua, Zheng Shou-Hong, Huang You-Lin, Tao Xiao-Ma
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  • Silicate cathode material Li2CoSiO4 has received wide attention due to high theoretical capacity. However, the high discharge makes the existing electrolyte unable to satisfy the requirements of its use, and the poor cyclic stability limits its further application and development. The high discharge and cycle stability of Li2CoSiO4 cathode material can be improved by doping corresponding elements. The effects of non-transition high-valent elements of Ga, Ge and As doping on structural, electrochemical and electronic properties of Li-ion battery cathode material Li2CoSiO4 are systematically studied by the first-principles calculations based on density functional theory within the generalized gradient approximation with Hubbard corrections (GGA + U). The calculation results show that the maximum expansion range of the unit cell volume of Li2CoSiO4 cathode material during lithium ion removal is 3.5%. However, the Ga, Ge and As doping reduce the variation range of unit cell volume during the delithiation of the system, which is beneficial to the improvement of the cycle stability of Li2CoSiO4 material. Furthermore, the Ga, Ge and As doping can reduce the theoretical average deintercalation voltages of extraction for the first Li+ in per formula unit; the theoretical average deintercalation voltages of the doping systems decrease by 1.65 V, 1.64 V and 1.64 V, respectively, compared with the deintercalation voltage of the undoped Li2CoSiO4 system. Meanwhile, except for the Ga doping, the Ge and As doping can also effectively reduce their theoretical average deintercalation voltagesin the secondary delithiation process. The density of states and magnetic moment show that Co2+ has a strong binding effect on the 3d orbital electrons, which makes it difficult for Co2+ in Li2CoSiO4 material to lose electrons for participating in the charge compensation in the process of Li+ removal. However, the Ga, Ge and As doping can effectively participate in the charge compensation of the system in the process of Li+ removal, which is the main reason for the decrease of the theoretical average deintercalation voltage of the system. In addition, the Ge doping reduces the band gap value of the Li2CoSiO4 from 3.7 eV to 2.49 eV, while the Ga doping and the As doping introduce the donor defects, and thus making the doping system exhibit metallic properties, which can improve the conductivity of the system to some extent.
      Corresponding author: Hou Yu-Hua, hyhhyl@163.com
    • Funds: Project supported by the National Natural Science Foundation of China (Grant No. 11304146) and the Scientific Research Fundation of the Education Department of Jiangxi Province, China (Grant Nos. GJJ170587, GJJ160713).

    随着工业社会的快速发展, 受日益增长的能源需求和日益枯竭的化石燃料影响, 迫使人们不断寻找可持续的能源替代品或储能材料[14]. 同时, 由于环境污染日益严重, 使得石油、煤炭等化石能源的使用受到广泛限制. 因此, 发展绿色可再生能源受到全世界的广泛关注. 太阳能、风能和水力发电等可循环的绿色能源将最终代替传统能源, 但这些绿色能源存在不可控性和间歇性, 因此寻找先进的储能材料或能源转换材料受到重视[57]. 硅酸盐类正极材料Li2MSiO4 (M = Mn, Fe和Co)因具有高比容量(理论比容量高达330 mA·h/g)[8]、主体结构稳定性(具有稳定的Si—O共价键)[9]和结构多样性[10]等特点而受到广泛关注.

    硅酸盐类正极材料Li2CoSiO4因具有较高的放电平台, 导致现有的电解液无法满足其使用要求[11], 并且由于较差的循环特性[10], 使得其应用受到限制. 关于Li2CoSiO4性能改善的研究一直是人们关注的热点. Lyness等[10]对多晶型Li2CoSiO4进行了系统研究, 发现经过球磨处理后, 其电化学性能得到显著提高, 但其在首次放电过程中的放电比容量仅为33 mA·h/g, 其中βI相结构材料经过碳包覆处理后与经过球磨处理的材料相比其放电比容量上升至60 mA·h/g. Zhang等[12]运用P元素对Li2CoSiO4/C进行掺杂, 研究表明P掺杂可使体系首次的放电比容量增大至144 mA·h/g, 证明了Li2CoSiO4有可能成为高性能的锂离子电池正极材料. Wu等[13]运用第一性原理的方法对Na掺杂Li2CoSiO4进行了理论研究, 发现Na离子掺杂可有效降低电子结构的禁带宽度, 提高材料的导电性, 并且Na离子掺杂可使晶体结构沿b轴方向发生膨胀, 有助于Li离子的扩散. Du等[14]采用Al掺杂碳包覆Li2CoSiO4的方法, 有效地改善了其电化学性能, 当Al含量为4%时获得最优结果, 使得其在首次充放电过程中的充放电比容量分别为331和140 mA·h/g, 并且在后续的循环过程中其放电比容量并未显著衰减.

    有关Li2CoSiO4正极材料机理方面的研究鲜有报道. 本文尝试构建Ga, Ge和As分别代替Li2CoSiO4中50%的Co原子形成Li2Co0.5R0.5SiO4 (R = Ga, Ge和As)结构, 并运用第一性原理的方法, 详细系统地研究掺杂对Li2CoSiO4正极材料结构稳定性、理论脱嵌电压、电子结构和磁矩等参数的影响.

    本文采用基于密度泛函理论框架下的投影缀加波法进行计算[15], 计算软件包为VASP(Vienna ab initio simulation package)[16,17]. 交换关联能选取广义梯度近似(generalized gradient approximation, GGA)条件下的Perdew-Burke-Ernzerhof泛函[18]. 电子在自洽过程中的能量收敛标准为1.0 × 10–6 eV, 作用在每个原子上的力不大于0.01 eV/Å, 截断能的取值为500 eV, 布里渊区的K点用Monkhorst-Pack方法产生, 生成9 × 9 × 9的网格K点进行优化. 由于过渡族金属Co中3d轨道电子之间的强关联相互作用, 本文采取加入Hubbard参数U进行修正[19,20]. 在GGA + U的框架下, 过渡金属Co的U值经过测试后选取U = 5.5 eV, 所有的计算均在自旋极化条件下进行.

    通过X射线衍射分析发现[21], Li2CoSiO4是空间群为Pmn21的正交结构, 其晶格常数为a = 6.2558 Å, b = 5.3584 Å和c = 4.9357 Å. 本文在GGA + U条件下优化获得的晶格常数为a = 6.1872 Å, b = 5.4420 Å和c = 4.9841 Å, 与实验值符合较好, 表明GGA + U算法的应用符合该体系. Li2CoSiO4晶胞中含有4个Li, 2个Co, 2个Si和8个O, 其中CoO4四面体与SiO4四面体通过O原子相互连接, 构成[CoSiO4]四面体层, 且沿c轴方向, CoO4四面体与SiO4四面体通过O原子相互连接形成的链状结构具有一定程度的褶皱. LiO4四面体也通过O原子相互连接形成[LiO4]四面体层. 最终, [CoSiO4]四面体层和[LiO4]四面体层沿着b轴交替排列, 形成二维层状材料. 本文尝试采用Ga, Ge和As原子分别代替50%的Co原子, 形成Li2Co0.5R0.5SiO4 (R = Ga, Ge, As)结构, 如图1所示.

    Figure 1.  (a) Crystal cell structure of Li2Co0.5R0.5SiO4 (R = Co, Ga, Ge and As); (b) the corresponding supercell. Green, pink, orange and blue tetrahedron represent LiO4, CoO4, RO4 and SiO4, respectively.

    LixCo0.5R0.5SiO4 (R = Co, Ga, Ge, As; x = 0, 1, 2)在脱锂过程中的晶胞体积变化如图2所示. 由图2可知, Ga, Ge和As的掺杂使Li2Co0.5R0.5SiO4(R = Ga, Ge和As)晶胞体积与Li2CoSiO4相比分别膨胀2.82%, 5.33%和5.6%. 此外由图2可知, LixCoSiO4 (x = 0, 1, 2)在脱锂过程中晶胞体积呈持续膨胀变化, 与Li2CoSiO4相比, LiCoSiO4与CoSiO4的晶胞体积膨胀率分别为0.73%和3.5%(数值为正代表晶胞体积膨胀, 为负代表晶胞体积收缩). Ga和Ge掺杂使体系的晶胞体积在脱锂过程中呈现先减小后增大的变化趋势: 对于Li2Co0.5Ga0.5SiO4结构, 与Li2Co0.5Ga0.5SiO4相比, LiCo0.5Ga0.5SiO4和Co0.5Ga0.5SiO4的晶胞体积变化率分别为–1.66%和1.99%; 而对于Li2Co0.5Ge0.5SiO4结构, 与Li2Co0.5Ge0.5SiO4相比, LiCo0.5Ge0.5SiO4和Co0.5Ge0.5SiO4的晶胞体积变化率分别为–2.46%和–1.57%. As掺杂使Li2Co0.5As0.5SiO4的晶胞体积在脱锂过程中呈现先增大后减小的变化趋势, 与Li2Co0.5As0.5SiO4相比, LiCo0.5As0.5SiO4和Co0.5As0.5SiO4的晶胞体积变化率分别为0.56%和–2.73%.

    Figure 2.  Corresponding unit cell volume of LixCo0.5R0.5SiO4 (R = Co, Ga, Ge and As) at during delithiation x (x = 0, 1, 2).

    LixCo0.5R0.5SiO4 (R = Co, Ga, Ge, As; x = 0, 1, 2)脱锂过程中晶格常数的变化如图3所示. 由图3可知, LixCo0.5R0.5SiO4 (R = Co, Ga, Ge, As; x = 0, 1, 2)在整脱锂过程中晶格常数a均呈缩短的趋势, 这是因为在脱锂过程中由于Li+的脱离, 体系中的R离子需要提供相应的电子, 用以提供电荷补偿, 所以R2+离子会被氧化为更高的价态, 从而使R—O键的键长缩短[2225], 造成晶格常数a表现为缩短趋势. 对于晶格常数b, 在脱锂过程中均表现出增长的趋势, 这是因为在脱锂过程中由于Li+的脱离, [LiO4]四面体层对其相邻的[Co0.5R0.5SiO4]四面体层之间的束缚作用减弱, 进而使晶格常数b发生增长. 而晶格常数c却在脱锂过程中表现为略有浮动的不确定变化, 这取决于R—O键长的缩短和沿c轴方向上的链褶皱被缓解之间的相互作用[26].

    Figure 3.  Variations of lattice parameters a, b and c of LixCo0.5R0.5SiO4 (R = Co, Ga, Ge, As) at during delithiation x (x = 0, 1, 2).

    根据电极材料脱锂前后反应物与生成物之间的基态体系能量差值, 可以计算出电极材料的理论平均脱嵌电压[2731], 其计算公式如下:

    $ \begin{array}{l} \bar V =\\ \dfrac{{\left| {{E_{{\rm{coh}}}}\left[ {{\rm{L}}{{\rm{i}}_{{x_1}}}{\rm{Host}}} \right] \!-\! {E_{{\rm{coh}}}}\left[ {{\rm{L}}{{\rm{i}}_{{x_2}}}{\rm{Host}}} \right] \!-\! \left( {{x_1}\! -\! {x_2}} \right){E_{{\rm{coh}}}}\left[ {{\rm{Li}}} \right]} \right|}}{{{x_1} - {x_2}}} \end{array}$

    (1)

    其中$E_{\rm coh}\left[ {\rm Li}_{x_1}{\rm Host} \right] $表示脱锂前单位公式体系的折合能, $ E_{\rm coh}\left[ {\rm Li}_{x_2}{\rm Host} \right]$表示脱锂后单位公式体系的折合能, $E_{\rm coh}\left[ {\rm Li}\right] $表示BCC结构Li单质的原胞能量; x1, x2分别表示脱锂前后单位公式体系的Li+浓度. 根据计算得出的Li2Co0.5R0.5SiO4 (R = Co, Ga, Ge, As)理论平均脱嵌电压, 如图4所示.

    Figure 4.  Average deintercalation voltages of Li2Co0.5R0.5SiO4 (R = Co, Ga, Ge and As).

    图4A2+/A3+A3+/A4+分别表示体系一次脱锂与二次脱锂时的理论平均脱嵌电压. 经过计算可知, Li2CoSiO4电极材料一次脱锂时的理论平均脱嵌电压为4.17 V, 与实验值4.2 V[5]符合较好. 此外通过图4可知, 在A2+/A3+的情况下, Ga, Ge和As掺杂均降低了体系的理论平均脱嵌电压, 其降低值分别为1.65, 1.64和1.64 V. 同时, 在A3+/A4+情况下, 除Ga掺杂外, Ge和As掺杂也都降低了体系的理论平均脱嵌电压, 其降低值分别为0.69和1.47 V.

    为了厘清Ga, Ge和As掺杂对LixCoSiO4 (x = 0, 1, 2)电极材料电子结构的影响, 本文计算了LixCo0.5R0.5SiO4 (R = Co, Ga, Ge, As; x = 0, 1, 2)的总态密度(TDOS)和分波态密度(PDOS)图. 图5给出了未掺杂结构LixCoSiO4 (x = 0, 1, 2)的电子态密度图. 由图5可知Li2CoSiO4的带隙值为3.7 eV, 与文献[32]结果一致. 随着Li+的不断脱离, LiCoSiO4和CoSiO4的带隙值分别为1.92 eV和1.13 eV, 均表现出半导体特性, 且带隙值伴随Li+的脱离不断减小.

    Figure 5.  Density of states of (a) Li2CoSiO4; (b) LiCoSiO4; (c) CoSiO4.

    为了厘清脱锂过程中Co离子的价态变化, 表1列出了LixCoSiO4 (x = 0, 1, 2)在不同Li+浓度下Co离子的磁矩参数. 在A2+/A3+的情况下, 结合图5(a)图5(b)表1可知, 伴随Li+的脱离, Co离子自旋向下的电子态密度发生了明显的变化, 在禁带处出现了来自于Co离子3d轨道的自旋向下未被占据态, 并且其磁矩由2.79 μB变化为3.18 μB. 以上结果表明, 当单位公式内脱离一个Li+时, Co离子参与了体系的电荷补偿, 由+2价氧化至+3价. 在A3+/A4+的情况下, 由图5(b)图5(c)表1可知, 在费米能级以上的空带处出现了自旋向下的O离子2p轨道的未被占据态, Co离子3d轨道的电子态密度并未发生明显改变, 并且Co离子的磁矩变化不大, 表明当单位公式内第二个Li+脱离时, 体系的电荷补偿主要是由–2价O离子提供的, 其价态由–2价氧化为–(2 – λ)(0 < λ < 1)价.

    Table 1.  Magnetic moment and oxidation state of Co ion.
    结构磁矩/μB氧化态
    Li2CoSiO42.79+2 (4s03d7)
    LiCoSiO43.18+3 (4s03d6)
    CoSiO43.34+3 (4s03d6)
     | Show Table
    DownLoad: CSV

    图6给出了LixCo0.5Ga0.5SiO4 (x = 0, 1, 2)在脱锂过程中的TDOS和PDOS. 由图6(a)图6(d)可知, Li2Co0.5Ga0.5SiO4具有金属特性, 其主要原因是由于Ga3+替换了Co2+, 导致在费米能级处引入了施主缺陷[33]. 由图6(b)图6(c)可知, LiCoSiO4表现为半导体特性, 其带隙值为1.95 eV, 而Co0.5Ga0.5SiO4由于O离子的2p轨道电子态密度穿过费米能级, 表现出金属特性.

    Figure 6.  Density of states of (a) Li2Co0.5Ga0.5SiO4, (b) LiCo0.5Ga0.5SiO4, (c) Co0.5Ga0.5SiO4; (d) the PDOS of Ga in LixCo0.5Ga0.5SiO4 (x = 0, 1, 2) during delithiation.

    表2列出了LixCo0.5Ga0.5SiO4(x = 0, 1, 2)在不同Li+浓度下Co离子的磁矩参数. 在A2+/A3+的情况下, 结合图6(a)图6(b)图6(d)表2可知, 伴随Li+的脱离, 在空带中出现了Co离子3d轨道的部分未被占据态和Ga离子4s轨道的完全未被占据态, 并且Co离子的磁矩由2.79 μB变为3.18 μB, 说明在一次脱锂的过程中Co离子和Ga离子均参与了体系的电荷补偿, Co离子由+2价氧化为+3价, Ga离子表现出+3价. 在A3+/A4+的情况下, 由图6(c)可知, 伴随Li+的脱离, 在费米能级和禁带处出现了由–2价O离子提供的未被占据态, Co离子的电子态密度并未发生明显改变, 而且通过表2可知, Co离子的磁矩仅由3.18 μB变为3.26 μB, 几乎未发生改变, 说明在二次脱锂过程中, 体系的电荷补偿主要由–2价O离子提供, 其价态由–2价氧化为–(2 – ψ)(0 < ψ < 1)价. 此外, 由图6(d)可知Ga3+并未参与体系二次脱锂过程中的电荷补偿.

    Table 2.  Magnetic moment and oxidation state of Co ion.
    结构磁矩/μB氧化态
    Li2Co0.5Ga0.5SiO42.79+2 (4s03d7)
    LiCo0.5Ga0.5SiO43.18+3 (4s03d6)
    Co0.5Ga0.5SiO43.26+3 (4s03d6)
     | Show Table
    DownLoad: CSV

    Ge掺杂LixCoSiO4 (x = 0, 1, 2)的TDOS和PDOS如图7所示. 由图7(a)图7(d)可知, Li2Co0.5Ge0.5SiO4表现出半导体特性, 带隙值为2.49 eV, 且在费米能级附近的自旋态密度主要由Ge离子的4s轨道提供. 由图7(b)图7(d)可知, LiCo0.5Ge0.5SiO4也表现出半导体特性, 带隙值为2.08 eV, 其带隙值下降的原因是在禁带处出现了Ge离子4s轨道的未被占据态. 图7(c)中Co0.5Ge0.5SiO4也显示出半导体特性, 带隙值为1.35 eV, 其带隙值下降的主要原因是在禁带处出现了部分自旋向下的Co离子3d轨道和O离子2p轨道的未被占据态.

    Figure 7.  Density of states of (a) Li2Co0.5Ge0.5SiO4, (b) LiCo0.5Ge0.5SiO4, (c) Co0.5Ge0.5SiO4; (d) the PDOS of Ge in LixCo0.5Ge0.5SiO4 (x = 0, 1, 2) during delithiation.

    不同Li+浓度下LixCo0.5Ge0.5SiO4 (x = 0, 1, 2)中Co离子的磁矩参数如表3所列. 在A2+/A3+的情况下, 结合图7(a)图7(b)图7(d)表3可知, 随着Li+的脱离, Ge离子4s轨道的未被占据态出现在禁带处, Co离子的电子态密度并未发生明显变化, 并且Co离子的磁矩在脱锂前后均为2.79 μB, 证明在一次脱锂的过程中, 体系的电荷补偿主要由+2价Ge离子提供, Ge离子由+2价氧化为+4价. 在A3+/A4+的情况下, 从图7(b)图7(c)可以看出, 在禁带处同时出现了Co离子3d轨道和O离子2p轨道自旋向下的部分未被占据态, 并且Co离子的磁矩由2.79 μB变为3.35 μB, 表明在体系的二次脱锂过程中, Co离子与O离子均参与了体系的电荷补偿, Co离子由+2价氧化为+3价, O离子由–2价氧化为–(2 – φ) (0 < φ < 1)价.

    Table 3.  Magnetic moment and oxidation state of Co ion.
    结构磁矩/μB氧化态
    Li2Co0.5Ge0.5SiO42.79+2 (4s03d7)
    LiCo0.5Ge0.5SiO42.79+2 (4s03d7)
    Co0.5Ge0.5SiO43.35+3 (4s03d6)
     | Show Table
    DownLoad: CSV

    LixCo0.5As0.5SiO4 (x = 0, 1, 2)的TDOS和PDOS如图8所示. 通过图8(a)图8(b)图8(d)可知, Li2Co0.5As0.5SiO4和LiCo0.5As0.5SiO4均呈现金属特性, 其主要原因是由于As离子的掺杂在费米能处引入了施主缺陷. 由图8(c)可知Co0.5As0.5SiO4表现出半导体特性, 其带隙为1.95 eV.

    Figure 8.  Density of states of (a) Li2Co0.5As0.5SiO4, (b) LiCo0.5As0.5SiO4, (c) Co0.5As0.5SiO4; (d) the PDOS of As in LixCo0.5As0.5SiO4 (x = 0, 1, 2) during delithiation.

    表4列出了LixCo0.5As0.5SiO4 (x = 0, 1, 2)在不同Li+浓度下Co离子的磁矩参数. 在A2+/A3+的情况下, 结合图8(a)图8(b)图8(d)表4可知, 伴随Li+的脱去, Co离子3d轨道的自旋态密度并未发生明显的变化, 其磁矩稳定地保持在2.79 μB; 而As离子的自旋态密度却发生了明显变化, 由图8(d)中的x = 1可知, As离子的4s轨道与4p轨道发生了明显的sp轨道杂化, 并出现在费米能级处, 表明在体系一次脱锂过程中, Co离子并未参与体系脱锂过程中的电荷补偿, 保持+2价不变, 而As离子掺杂却对体系的电荷补偿起到了主要作用, As离子价态由+3价氧化为+5价, 这也是导致体系在一次脱锂前后均呈现出金属特性的主要原因. 在A3+/A4+的情况下, 由图8(b)图8(c)图8(d)表4可知, Co离子的自旋态密度发生了变化, 其自旋向下的未被占据态增加, 磁矩由2.79 μB变化为3.26 μB; As离子在费米能级处的自旋态密度消失, 全部表现为未被占据态. 以上分析表明, 在体系的二次脱锂过程中Co离子与As离子均参与了体系的电荷补偿, Co离子由+2价氧化为+3价, As离子表现出+5价.

    Table 4.  Magnetic moment and oxidation state of Co ion.
    结构磁矩/μB氧化态
    Li2Co0.5As0.5SiO42.79+2 (4s03d7)
    LiCo0.5As0.5SiO42.79+2 (4s03d7)
    Co0.5As0.5SiO43.26+3 (4s03d6)
     | Show Table
    DownLoad: CSV

    对于图8(d)中, As离子的4s和4p轨道在费米能级以下出现的高度对称自旋态密度, 主要归因于As和O的电负性, 根据鲍林标度[34]其值分别为2.18和3.44, 相应的电负性差值小于1.7, 所以表现出一定的共价键特性[35], 因此在费米能级以下出现了高度对称的自旋电子态密度.

    本文运用第一性原理的方法计算了Ga, Ge和As掺杂对Li2CoSiO4电极材料结构特性、电化学特性和电子结构的影响. 计算结果表明, 在晶胞体积变化上, 掺杂Ga和Ge使结构体积在脱锂过程中表现出先减小后增大的趋势, 而掺杂As则表现出先增大后减小的趋势, 相比未掺杂体系, 掺杂Ga, Ge和As降低了体系脱锂前后体积的变化范围, 有利于提高Li2CoSiO4材料的循环稳定性; 在电化学特性上, 在A2+/A3+的情况下, Ga, Ge和As掺杂均有效降低了体系的理论平均脱嵌电压, 且在A3+/A4+的情况下, 除Ga掺杂使体系的理论平均脱嵌电压升高外, Ge和As掺杂也都有效降低了体系的理论平均脱嵌电压. 循环稳定性的提高和理论脱嵌电压的有效降低, 使得Li2CoSiO4的应用在理论上成为了可能. 通过分析电子态密度图和磁矩可知, Co2+对其3d轨道的电子具有强烈的束缚作用, 使得其在脱锂过程中, 3d轨道的电子难以失去, 这是Li2CoSiO4具有较高放电平台的主要原因之一. 而掺杂Ga, Ge和As使体系理论平均脱嵌电压有效降低的主要原因是掺杂离子参与了体系在脱锂过程中的电荷补偿.

    [1]

    Larcher D, Tarascon J M 2015 Nat. Chem. 7 19

    [2]

    Meng Y S, Dompablo M E A 2009 Energy Environ. Sci. 2 589Google Scholar

    [3]

    Ding Y F, Zhao Q Q, Yu Z L, Zhao Y Q, Liu B, He P B, Zhou H, Li K L, Yin S F, Cai M Q 2019 J. Mater. Chem. C 7 7433Google Scholar

    [4]

    Deng X Z, Zhao Q Q, Zhao Y Q, Cai M Q 2019 Curr. Appl. Phys. 19 279Google Scholar

    [5]

    Xu B, Qian D, Wang Z, Meng Y S 2012 Mater. Sci. Eng. R-Rep. 73 51Google Scholar

    [6]

    Zhao Y Q, Wang X, Liu B, Yu Z L, He P B, Wan Q, Cai M Q, Yu H L 2018 Org. Electron. 53 50Google Scholar

    [7]

    Zhao Y Q, Ma Q R, Liu B, Yu Z L, Yang J L, Cai M Q 2018 Nanoscale 10 8677Google Scholar

    [8]

    Dominko R, Bele M, Kokalj A, Gaberscek M, Jamnik J 2007 J. Power Sources 174 457Google Scholar

    [9]

    Sasaki H, Nemoto A, Moriya M, Miyahara M, Hokazono M, Katayama S, Akimoto Y, Nakajima A, Hirano S I 2015 Ceram. Int. 41 S680Google Scholar

    [10]

    Lyness C, Delobel B, Robert A A, Bruce P G 2007 Chem. Commun. 46 4890

    [11]

    嘉明珍 2017 博士学位论文(成都: 西南交通大学)

    Jia M Z 2017 Ph. D. Dissertation (Chengdu: Southwest Jiaotong University) (in Chinese)

    [12]

    Zhang Z F, Chen Z L, Zhang X H, Wu D Y, Li J 2018 Electrochim. Acta 264 166Google Scholar

    [13]

    Wu S Q, Zhu Z Z, Yang Y, Hou Z F 2009 Trans. Nonferrous Met. Soc. 19 182Google Scholar

    [14]

    Du H W, Zhang X H, Chen Z L, Wu D Y, Zhang Z F, Li J 2018 RSC Adv. 8 22813

    [15]

    Kresse G, Joubert D 1999 Phys. Rev. B 59 1758

    [16]

    Kresse G, Furthmüller J 1996 Comput. Mater. Sci. 6 15Google Scholar

    [17]

    Kresse G, Furthmüller J 1996 Phys. Rev. B 54 11169Google Scholar

    [18]

    Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865Google Scholar

    [19]

    Anisimov V I, Zaanen J, Andersen O K 1991 Phys. Rev. B 44 943Google Scholar

    [20]

    Zhou F, Cococcioni M, Marianetti C A, Morgan D, Ceder G 2004 Phys. Rev. B 70 235121Google Scholar

    [21]

    Robert A A, Lyness C, Ménétrier M, Bruce P G 2010 Chem. Mater. 22 1892Google Scholar

    [22]

    Zhou F, Cococcioni M, Kang K, Ceder G 2004 Electrochem. Commun. 6 1144Google Scholar

    [23]

    Graetz J, Hightower A, Ahu C C, Yazami R, Rez P, Fultz B 2002 J. Phys. Chem. B 106 1286

    [24]

    Marianetti C A, Kotliar G, Ceder G 2004 Phys. Rev. Lett. 92 196405Google Scholar

    [25]

    Zhong G H, Li Y L, Yan P, Liu Z, Xie M H, Lin H Q 2010 J. Phys. Chem. C 114 3693Google Scholar

    [26]

    Li L, Zhu L, Xu L H, Cheng T M, Wang W, Li X, Sui Q T 2014 J. Mater. Chem. A 2 4251Google Scholar

    [27]

    Zhang P, Hu C H, Wu S Q, Zhu Z Z, Yang Y 2012 Phys. Chem. Chem. Phys. 14 7346Google Scholar

    [28]

    Chakrabarti S, Thakur A K, Biswas K 2017 Electrochim. Acta 236 288Google Scholar

    [29]

    Li Y S, Cheng X, Zhang Y 2013 Electrochim. Acta 112 670Google Scholar

    [30]

    Wu S Q, Zhang J H, Zhu Z Z, Yang Y 2007 Curr. Appl. Phys. 7 611Google Scholar

    [31]

    嘉明珍, 王红艳, 陈元正, 马存良, 王辉 2015 物理学报 64 087101Google Scholar

    Jia M Z, Wang H Y, Chen Y Z, Ma C L, Wang H 2015 Acta Phys. Sin. 64 087101Google Scholar

    [32]

    Zhang P, Zheng Y, Wu S Q, Zhu Z Z, Yang Y 2014 Comput. Mater. Sci. 83 45Google Scholar

    [33]

    Huang Y L, Fan W B, Hou Y H, Guo K X, Ouyang Y F, Liu Z W 2017 J. Magn. Magn. Mater. 429 263Google Scholar

    [34]

    Boyd R J, Markus G E 1981 J. Chem. Phys. 75 5385Google Scholar

    [35]

    Pauling L 1960 The Nature of The Chemical Bond (London: Oxford University Press) p100

  • 图 1  (a) Li2Co0.5R0.5SiO4 (R = Co, Ga, Ge, As)晶胞结构; (b)相应的超胞结构(绿色、粉色、橙色和蓝色四面体分别表示LiO4, CoO4, RO4和SiO4)

    Figure 1.  (a) Crystal cell structure of Li2Co0.5R0.5SiO4 (R = Co, Ga, Ge and As); (b) the corresponding supercell. Green, pink, orange and blue tetrahedron represent LiO4, CoO4, RO4 and SiO4, respectively.

    图 2  LixCo0.5R0.5SiO4 (R = Co, Ga, Ge, As; x = 0, 1, 2)脱锂过程中体积的变化

    Figure 2.  Corresponding unit cell volume of LixCo0.5R0.5SiO4 (R = Co, Ga, Ge and As) at during delithiation x (x = 0, 1, 2).

    图 3  LixCo0.5R0.5SiO4 (R = Co, Ga, Ge, As; x = 0, 1, 2)脱锂过程中晶格常数a, bc的变化

    Figure 3.  Variations of lattice parameters a, b and c of LixCo0.5R0.5SiO4 (R = Co, Ga, Ge, As) at during delithiation x (x = 0, 1, 2).

    图 4  Li2Co0.5R0.5SiO4 (R = Co, Ga, Ge, As)体系的理论平均脱嵌电压

    Figure 4.  Average deintercalation voltages of Li2Co0.5R0.5SiO4 (R = Co, Ga, Ge and As).

    图 5  脱锂结构的态密度图 (a) Li2CoSiO4; (b) LiCoSiO4; (c) CoSiO4

    Figure 5.  Density of states of (a) Li2CoSiO4; (b) LiCoSiO4; (c) CoSiO4.

    图 6  脱锂结构(a) Li2Co0.5Ga0.5SiO4, (b) LiCo0.5Ga0.5SiO4, (c) Co0.5Ga0.5SiO4的态密度图; (d)在脱锂过程中LixCo0.5Ga0.5SiO4(x = 0, 1, 2)中Ga的PDOS图

    Figure 6.  Density of states of (a) Li2Co0.5Ga0.5SiO4, (b) LiCo0.5Ga0.5SiO4, (c) Co0.5Ga0.5SiO4; (d) the PDOS of Ga in LixCo0.5Ga0.5SiO4 (x = 0, 1, 2) during delithiation.

    图 7  脱锂结构(a) Li2Co0.5Ge0.5SiO4, (b) LiCo0.5Ge0.5SiO4, (c) Co0.5Ge0.5SiO4的态密度图; (d)表示在脱锂过程中LixCo0.5Ge0.5SiO4 (x = 0, 1, 2)中Ge的PDOS

    Figure 7.  Density of states of (a) Li2Co0.5Ge0.5SiO4, (b) LiCo0.5Ge0.5SiO4, (c) Co0.5Ge0.5SiO4; (d) the PDOS of Ge in LixCo0.5Ge0.5SiO4 (x = 0, 1, 2) during delithiation.

    图 8  脱锂结构(a) Li2Co0.5As0.5SiO4, (b) LiCo0.5As0.5SiO4, (c) Co0.5As0.5SiO4的态密度图; (d)在脱锂过程中LixCo0.5As0.5SiO4 (x = 0, 1, 2)中As的PDOS

    Figure 8.  Density of states of (a) Li2Co0.5As0.5SiO4, (b) LiCo0.5As0.5SiO4, (c) Co0.5As0.5SiO4; (d) the PDOS of As in LixCo0.5As0.5SiO4 (x = 0, 1, 2) during delithiation.

    表 1  Co离子的磁矩和氧化态

    Table 1.  Magnetic moment and oxidation state of Co ion.

    结构磁矩/μB氧化态
    Li2CoSiO42.79+2 (4s03d7)
    LiCoSiO43.18+3 (4s03d6)
    CoSiO43.34+3 (4s03d6)
    DownLoad: CSV

    表 2  Co离子的磁矩和氧化态

    Table 2.  Magnetic moment and oxidation state of Co ion.

    结构磁矩/μB氧化态
    Li2Co0.5Ga0.5SiO42.79+2 (4s03d7)
    LiCo0.5Ga0.5SiO43.18+3 (4s03d6)
    Co0.5Ga0.5SiO43.26+3 (4s03d6)
    DownLoad: CSV

    表 3  Co离子的磁矩和氧化态

    Table 3.  Magnetic moment and oxidation state of Co ion.

    结构磁矩/μB氧化态
    Li2Co0.5Ge0.5SiO42.79+2 (4s03d7)
    LiCo0.5Ge0.5SiO42.79+2 (4s03d7)
    Co0.5Ge0.5SiO43.35+3 (4s03d6)
    DownLoad: CSV

    表 4  Co离子的磁矩和氧化态

    Table 4.  Magnetic moment and oxidation state of Co ion.

    结构磁矩/μB氧化态
    Li2Co0.5As0.5SiO42.79+2 (4s03d7)
    LiCo0.5As0.5SiO42.79+2 (4s03d7)
    Co0.5As0.5SiO43.26+3 (4s03d6)
    DownLoad: CSV
  • [1]

    Larcher D, Tarascon J M 2015 Nat. Chem. 7 19

    [2]

    Meng Y S, Dompablo M E A 2009 Energy Environ. Sci. 2 589Google Scholar

    [3]

    Ding Y F, Zhao Q Q, Yu Z L, Zhao Y Q, Liu B, He P B, Zhou H, Li K L, Yin S F, Cai M Q 2019 J. Mater. Chem. C 7 7433Google Scholar

    [4]

    Deng X Z, Zhao Q Q, Zhao Y Q, Cai M Q 2019 Curr. Appl. Phys. 19 279Google Scholar

    [5]

    Xu B, Qian D, Wang Z, Meng Y S 2012 Mater. Sci. Eng. R-Rep. 73 51Google Scholar

    [6]

    Zhao Y Q, Wang X, Liu B, Yu Z L, He P B, Wan Q, Cai M Q, Yu H L 2018 Org. Electron. 53 50Google Scholar

    [7]

    Zhao Y Q, Ma Q R, Liu B, Yu Z L, Yang J L, Cai M Q 2018 Nanoscale 10 8677Google Scholar

    [8]

    Dominko R, Bele M, Kokalj A, Gaberscek M, Jamnik J 2007 J. Power Sources 174 457Google Scholar

    [9]

    Sasaki H, Nemoto A, Moriya M, Miyahara M, Hokazono M, Katayama S, Akimoto Y, Nakajima A, Hirano S I 2015 Ceram. Int. 41 S680Google Scholar

    [10]

    Lyness C, Delobel B, Robert A A, Bruce P G 2007 Chem. Commun. 46 4890

    [11]

    嘉明珍 2017 博士学位论文(成都: 西南交通大学)

    Jia M Z 2017 Ph. D. Dissertation (Chengdu: Southwest Jiaotong University) (in Chinese)

    [12]

    Zhang Z F, Chen Z L, Zhang X H, Wu D Y, Li J 2018 Electrochim. Acta 264 166Google Scholar

    [13]

    Wu S Q, Zhu Z Z, Yang Y, Hou Z F 2009 Trans. Nonferrous Met. Soc. 19 182Google Scholar

    [14]

    Du H W, Zhang X H, Chen Z L, Wu D Y, Zhang Z F, Li J 2018 RSC Adv. 8 22813

    [15]

    Kresse G, Joubert D 1999 Phys. Rev. B 59 1758

    [16]

    Kresse G, Furthmüller J 1996 Comput. Mater. Sci. 6 15Google Scholar

    [17]

    Kresse G, Furthmüller J 1996 Phys. Rev. B 54 11169Google Scholar

    [18]

    Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865Google Scholar

    [19]

    Anisimov V I, Zaanen J, Andersen O K 1991 Phys. Rev. B 44 943Google Scholar

    [20]

    Zhou F, Cococcioni M, Marianetti C A, Morgan D, Ceder G 2004 Phys. Rev. B 70 235121Google Scholar

    [21]

    Robert A A, Lyness C, Ménétrier M, Bruce P G 2010 Chem. Mater. 22 1892Google Scholar

    [22]

    Zhou F, Cococcioni M, Kang K, Ceder G 2004 Electrochem. Commun. 6 1144Google Scholar

    [23]

    Graetz J, Hightower A, Ahu C C, Yazami R, Rez P, Fultz B 2002 J. Phys. Chem. B 106 1286

    [24]

    Marianetti C A, Kotliar G, Ceder G 2004 Phys. Rev. Lett. 92 196405Google Scholar

    [25]

    Zhong G H, Li Y L, Yan P, Liu Z, Xie M H, Lin H Q 2010 J. Phys. Chem. C 114 3693Google Scholar

    [26]

    Li L, Zhu L, Xu L H, Cheng T M, Wang W, Li X, Sui Q T 2014 J. Mater. Chem. A 2 4251Google Scholar

    [27]

    Zhang P, Hu C H, Wu S Q, Zhu Z Z, Yang Y 2012 Phys. Chem. Chem. Phys. 14 7346Google Scholar

    [28]

    Chakrabarti S, Thakur A K, Biswas K 2017 Electrochim. Acta 236 288Google Scholar

    [29]

    Li Y S, Cheng X, Zhang Y 2013 Electrochim. Acta 112 670Google Scholar

    [30]

    Wu S Q, Zhang J H, Zhu Z Z, Yang Y 2007 Curr. Appl. Phys. 7 611Google Scholar

    [31]

    嘉明珍, 王红艳, 陈元正, 马存良, 王辉 2015 物理学报 64 087101Google Scholar

    Jia M Z, Wang H Y, Chen Y Z, Ma C L, Wang H 2015 Acta Phys. Sin. 64 087101Google Scholar

    [32]

    Zhang P, Zheng Y, Wu S Q, Zhu Z Z, Yang Y 2014 Comput. Mater. Sci. 83 45Google Scholar

    [33]

    Huang Y L, Fan W B, Hou Y H, Guo K X, Ouyang Y F, Liu Z W 2017 J. Magn. Magn. Mater. 429 263Google Scholar

    [34]

    Boyd R J, Markus G E 1981 J. Chem. Phys. 75 5385Google Scholar

    [35]

    Pauling L 1960 The Nature of The Chemical Bond (London: Oxford University Press) p100

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Metrics
  • Abstract views:  8788
  • PDF Downloads:  110
  • Cited By: 0
Publishing process
  • Received Date:  04 April 2019
  • Accepted Date:  29 June 2019
  • Available Online:  01 September 2019
  • Published Online:  20 September 2019

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