First-Principles Study: Tuning the Redox Behavior of Lithium-Rich

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First-Principles Study: Tuning the Redox Behavior of Li-Rich Layered Oxides by Chlorine Doping Huijun Yan, Biao Li, Zhen Yu, Wangsheng Chu, and Dingguo Xia J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b01168 • Publication Date (Web): 14 Mar 2017 Downloaded from http://pubs.acs.org on March 16, 2017

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The Journal of Physical Chemistry

First-Principles Study: Tuning the Redox Behavior of Li-Rich Layered Oxides by Chlorine Doping Huijun Yan1, Biao Li1, Zhen Yu2, Wangsheng Chu2, Dingguo Xia1* 1

Beijing Key Laboratory of Theory and Technology for Advanced Batteries Materials, College

of Engineering, Peking University, Beijing 100871, P. R. China; 2

National Synchrotron Radiation Laboratory, University of Science and Technology of China,

Hefei 230029, P. R. China.

ABSTRACT: Lithium-rich layered oxides (LLOs) are promising cathode materials for next generation lithium ion batteries with high energy density. However, the charge cutoff potential of 4.8V constrains seriously the actual application of LLOs. Herein, using density functional theory (DFT) calculation, we investigated the tuning mechanism of chlorine doping on the redox potential and redox process in LLOs. The results showed that chlorine doping can decrease the charge potential, modulate the ratio of two redox couples of cation and anion, and lower the band gap of LLOs. These tunings were beneficial for the modification of the safety, cycling stability and voltage decay of LLOs materials. This work opens up a new route in terms of performance improvement via tuning of redox behavior based on deep understanding of anion doping mechanism.

/ 26Environment ACS Paragon1Plus


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INTRODUCTION Li-rich layered oxides (LLOs) with intermixed nano-domains composed of trigonal LiMO2 and monoclinic Li2MnO3 possess high capacity (>250mAh/g), low cost and environmental friendliness and have been regarded as the promising cathode materials for next generation lithium ion batteries with high energy density.1-5 The origin of high capacity for LLOs involves in two redox couples of cation and anion.6-8 Under charge cutoff potential ranging up to 4.8V, the anion oxygen participates in charge compensation by a plateau at ~4.5V (vs Li+/Li),9-11 usually coupling with the O2 evolution derived from the oxidation of O2- and the migration of transition metal.12-14 As a result, LLOs suffer from the voltage decay resulted from the transition of layer to spinel phase and the potential safety concerns during a prolonged cycling, which limit the practical application of LLOs.15 To overcome these problems, substantial experimental efforts have been made to optimize the LLOs cathode material for better electrochemical behavior.16 Li et al. proposed a way to lower the energy level of O-2p band by the polyanion (BO3/BO4) doping to enhance the oxygen stability and cycling reversibility.17 Saubanere et al. suggested the metal-driven reductive coupling mechanism to explain the origin of high capacity for LLOs. They thought that the enhanced degree of TM-O covalency could promote the oxygen redox activity and prevent O2 gas release,18-20 such as doping 4d-metal Mo/Nb/Ru.21-23 Except cation doping, some other works indicated that the cathode materials with anion ion introduction could increase the corrosion reactance of HF-related acids in the electrolyte and modify the rate performance.24, 25 In addition, anion ion doping can avoid the undesirable occupation of redox active components, which usually reduce capacity. Therefore, anion doping would be regarded as a promising direction to enhance the electrochemical performance for engineering application of LLOs. However, the roles of anion doping seem to be conflicting among the reported works


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and the nature of doping is still under debate. Furthermore, the charge cut-off potential ranging up to 4.8V has shackled seriously the actual application of LLOs as cathode material for high energy density lithium ion batteries,26, 27 whereas there were rare reports that involved the tuning of such high charge potential,28 causing potential safety concern and low cycle stability of lithium ion batteries.29-31 Therefore, it is highly desirable to lower the charge potential during the process of charge by tuning the redox behavior of LLOs. Here, we first showed that the redox behavior of LLOs can be modulated by chlorine anion doping, and presented some predictions about where the chlorine ion occupies and how to tune the charge potential of LLOs by chlorine doping, using a common tool Density Functional Theory (DFT) calculations.32-34 As Li-rich compound Li[LixNi1−x]O2 was previously reported,3537

and chlorine doping of related materials such as spinel LiMn2O4 and LiFePO4 were well

established,38-40 we selected the Li-rich single Ni-based compound Li1+xNi1-xO2 as the model material to reveal the effect of chlorine doping in order to avoid the coupling effect of various transition metals. METHODS All the structures were relaxed with the Vienna Ab-inito Simulation Package (VASP).41 The GGA+U framework with the Projector Augmented Wave (PAW) pseudopotential was used.42, 43 The value of U was fixed to 6.3eV for Ni-3d electrons referring to the previous literatures.44, 45 A supercell LiNiO2 (Li27Ni27O54) was constructed. Three Ni atoms were substituted by Li atoms, and lithium-rich compound Li1.11Ni0.89O2 (Li27[Li3Ni24]O54) was formed. Similarly, the structures of Li1.11Ni0.89O2-yAy (A=F, Cl, Br) were all obtained through oxygen substituted by halogen atoms in Li1.11Ni0.89O2. We considered the lowest energy configuration as the discussion object.



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More details can be seen in supporting information. The structures of Li1.11Ni0.89O2 (Li30Ni24O54) and Li1.11Ni0.89O2-yCly (y=0.11, 0.22, 0.33 and 0.44) are illustrated in Figure 1 and Figure S1. The small chlorine dopant concentration, especially dopant concentration y≤0.22, has a little effect on the capacity. The Li1.11Ni0.89O1.89A0.11 (A=F, Br) configurations were exhibited in Figure S2. The cut-off energy was 600eV and the 1*1*1 k-points in the Brillouin zone were used.46 The calculations with 0.05eV/Å of convergence on each atom were done. Spin polarized calculations were considered in all cases.

Figure 1. The optimized structures of Li1.11Ni0.89O2 (a) and Li1.11Ni0.89O1.89Cl0.11 (b); the local NiO6 configuration in Li1.11Ni0.89O2 (c); and the NiO5Cl configuration in Li1.11Ni0.89O1.89Cl0.11 (d); The length of Ni-O(Cl) bonds measured in angstrom were also labeled. RESULTS AND DISCUSSION Structural stability


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The high-capacity of LLOs involves in two redox couples of cation and anion. The structural stability of LLOs was influenced after the large contribution of oxygen anion redox to capacity, such as the collapse of structure, electrolyte decomposition and transition of layer to spinel phase.29-31, 47, 48 Therefore, the structural stability in LLOs is very critical to obtain the LLOs with a prolonged cycling high capacity. As illustrated in Figure 1 and Figure S1, the relaxed structures show that the chlorine atoms occupy the oxygen sites and maintain structural stability well after chlorine doping. Compared with the structure of lithium-rich Li1.11Ni0.89O2, the electronic structures of some nickel ions changed because of chlorine atoms introduction. Different with LiNiO2, there are three oxidation states of Ni ions in lithium-rich Li1.11Ni0.89O2 resulted from the disproportionation reaction: 2Ni3+→Ni2++Ni4+ owing to the substitution of some Ni3+ by Li+ ions. The Ni4+ with (t2g↑)3(t2g↓)3 configuration in pristine NiO6 octahedral (Figure 2a) was reduced to Ni3+ with (t2g↑)3(t2g↓)3(eg↑)1 configuration in NiO5Cl octahedral after Cl introduction (Figure 2b). And minor Ni2+ ions with (t2g↑)3 (t2g↓)3(eg↑)2 configuration in NiO6 octahedral in the side of the corresponding NiO5Cl octahedral (Figure 2c) were oxidized to Ni3+ with (t2g↑)3(t2g↓)3(eg↑)1 configuration (Figure 2d). Other Ni ions remained the original valence in the NiO6 octahedral distant to the corresponding NiO5Cl octahedral (Figure S3). The electrons in orbital of Ni3+ for NiO5Cl have a strong repulsion to the p orbital electrons of ligand O/Cl, causing the increase of Ni-O/Ni-Cl bond length (Figure 1d) compared to that of Li1.11Ni0.89O2 (Figure 1c). The longer Ni-O bond length would result in the decreased covalency of the Ni-O bonds. As suggested by many previous reports, the strong covalency of active metals with oxygen will promote the generation of the electronic holes in the oxygen 2p band and induce the evolution of oxygen when deep charging.49,

50

Therefore, the decreased Ni-O covalence will

alleviate the variation of the oxygen 2p band during cycling, implying the improvement of the



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structural stability. In addition, the interaction between e g orbital of transition metal and oxygen b ∗ ∗ p orbital result in the formation of eg bonding orbital and eg anti-bonding orbital.51 And the eg b anti-bond mainly contains the metal d states, whereas the eg bond is consist of O-p states.

Because of the increased Ni3+ ions after chlorine doping, the d z 2 / d x 2 − y 2 orbital electrons in Ni3+ mainly occupy eg anti-bonding orbital, leading to the increase of system energy and replying a ∗

decreased deintercalation lithium potential. As we known, the decreased charge potential will be helpful for the stability of LLOs owing to the alleviation of decomposition of electrolyte.


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Figure 2. The orbital electronic structure of Ni-3d in some NiO6/NiO5Cl octahedrons of Li1.11Ni0.89O2 (a,c) and Li1.11Ni0.89O1.89Cl0.11 (b,d). The Fermi level was set to be 0eV. To further determine that whether chlorine participated in charge compensation during charging process, we performed the average charge analysis and the charge density differences between Li1.11Ni0.89O2-yCly and Ni0.89O2-yCly (Figure 3). According to the average charge results (Table S1), oxygen ions predominate the charge compensation during the whole charging process. The contribution of chlorine ions with smaller concentration can be neglected though per chlorine atom contributes equivalence to the redox process compared with oxygen. Therefore the charge density change of chlorine ions can hardly be observed from the charge density differences (Figure 3 provide the cross section view, while Figure S4 give the whole distribution) for samples with small doped concentration (for y≤0.22). For y≥0.33, some chlorine ions provide small electrons in charging process (see Figure 3 and Figure S4), which would lead to a more complexity redox mechanism. The chlorine ions in the samples with smaller doped concentration (y≤0.22), which do not involve chlorine in redox, may serve as a framework to suppress the structural variation of electrode. Hence, our followed discussion will only consider the situation of chlorine concentration y≤0.22.



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Figure 3. The charge density differences between Li1.11Ni0.89O2-yCly and Ni0.89O2-yCly (y=0.11, 0.22, 0.33 and 0.44) were shown in a-d, respectively. The isosurface level was set to be 0.15. The charge

density

differences

were

∆ρ = ρ ( Li1.11Ni0.89O2− yCly ) − ρ ( Ni0.89O2− yCly )

calculated

by

the

equation

.

Previous works showed that the lithium-rich layered oxides were composed of two intermixed nano-domains of LiMnO2 and Li2MnO3.2, 3 The MnO3 resulted from the delithiation of Li2MnO3 possesses an irreversible O-O bond, which would give rise to structure collapse and O2

evolution.18

Here,

we

took

the

Li2NiO3

(Li4/3Ni2/3O2)

and

Li2NiO2.875Cl0.125

(Li4/3Ni2/3O1.92Cl0.08) as an example to evaluate the effect of chlorine doping on the formation of O-O bond. Figure 4a shows the structure of delithiated state NiO3 from Li2NiO3. Similarly, interlayer O-O bond is also formed in NiO3. However, for the Li2NiO2.875Cl0.125, its delithiated


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state NiO2.875Cl0.125 (Figure 4b) maintains structural stability well, and no O-O bond forms. During the first charge process of Li2NiO3, only O ions contribute electrons to compensate lithium deintercalation. The interlayer O-O bond will be formed in NiO3, which will ultimately end with O2 release. However, the formation of O-O dimers in Li2NiO3 should be a progressive process, which is similar to Li2MnO3, as reported previously.18 In Li2NiO2.875Cl0.125, the oxidation state of Ni ions will be reduced due to chlorine doping. So Ni ions will participate in charge compensation during charging, enabling less charge compensation occurs in O ions. Less holes are located on oxygen ions, which is beneficial for the stability of oxygen network. And there is no interlayer O-O bond formation in full delithiated phase NiO2.875Cl0.125. Therefore, chlorine doping could effectively improve the structural stability of LLOs cathode during charging process.

Figure 4. The structural responses of delithiated states NiO3 (a) and NiO2.875Cl0.125 (b); the 1.366 Å was the O-O bond length.



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Effect of chlorine doping on the charging potential Figure 5(a-c) exhibits the formation energies of different configurations upon the lithium extraction for Li1.11-zNi0.89O2, Li1.11-zNi0.89O1.89Cl0.11 and Li1.11-zNi0.89O1.78Cl0.22. The formation energies were calculated according to the equations in supporting information. The convex hull was the line connects the lowest energy phases along in the formation energy vs composition. The formation energies with different Li concentration are negative, indicating that Li1.11zNi0.89O2-yCly

is stable with respect to phase separation into a fraction of Li1.11Ni0.89O2-yCly and a

fraction of Ni0.89O2-yCly. It means that the deintercalation of Li ion proceeds by the topological way. Figure 5d shows the calculated charging curves of Li1.11Ni0.89O2-yCly (y=0, 0.11, 0.22) using these lowest energies at different compositions based on the equations in supporting information, regardless of the entropy and temperature effects. It can be seen that the whole delithiated voltage of Li1.11Ni0.89O2-yCly (y=0.11, 0.22) is slightly lower than that of Li1.11Ni0.89O2.

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Figure 5. Formation energies with different Li concentration in Li1.11-zNi0.89O2 (a), Li1.11zNi0.89O1.89Cl0.11 zNi0.89O2-yCly

(b) and Li1.11-zNi0.89O1.78Cl0.22 (c); the calculated charging curves of Li1.11-

(y=0, 0.11, 0.22) (d).

As a comparison, we also calculated the delithiated voltage for the F and Br doping. The O2p and Ni-3d orbital density of states (Figure 6) were obtained from the optimized structures of Li1.11Ni0.89O2 and Li1.11Ni0.89O1.89A0.11 (A=F, Cl, Br) (Figure 1 and Figure S2). The Fermi energy of systems was set to be 0 eV. The O-2p orbital density of states (blue dotted line) in Li1.11Ni0.89O1.89F0.11 is away from Fermi energy compared to Li1.11Ni0.89O2, indicating that it is more difficult for anion oxygen to lose electrons in Li1.11Ni0.89O1.89F0.11 compared to Li1.11Ni0.89O2. Namely, the oxidation potential of anion oxygen in Li1.11Ni0.89O1.89F0.11 would be / 26Environment ACS Paragon11 Plus


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enhanced. It is not conducive to the stability of the electrolyte. But Cl/Br doping makes the density of states of O-2p band closer to the Fermi level. This would be expected to improve the safety by reducing the redox potential of anion oxygen. For the density of states of nickel atoms (green dotted line), all the positions of Ni redox couples were all closer to Fermi energy after the halogen substitution, meaning that the cation redox potential will be decreased. Therefore, we calculated the average delithiated voltage for the F, Cl and Br doping. As shown in Table 1, it can be seen that F doping would enhance the delithiated potential, while Cl and Br doping would lower it. This was in agreement with previous works.53, 54 However, the Br doping could result in the formation of Br-O bond (See Figure S5), replying a collapse of LLOs structure. Therefore, we don’t discuss the effect of Br doping in the following discussion. As we have known, the charge voltage ranging up to 4.8V could cause the degradation of electrolyte and instability of LLOs, replying the decaying of capacity.29-31 The reduced delithiated potential resulted from the chlorine doping will be very helpful for the stability of batteries using LLOs as cathode for lithium ion batteries. Table 1. The average delithiated voltage of Li1.11Ni0.89O1.89A0.11 (A=F, Cl, Br) compared to Li1.11Ni0.89O2. Average delithiated voltage (V) Li1.11Ni0.89O2

4.22

Li1.11Ni0.89O1.89F0.11

4.26

Li1.11Ni0.89O1.89Cl0.11

4.06

Li1.11Ni0.89O1.89Br0.11

3.95


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Figure 6. The O-2p and Ni-3d orbital density of states in Li1.11Ni0.89O2 and Li1.11Ni0.89O1.89A0.11 (A=F, Cl, Br). The Fermi energy was set to be 0eV. The blue dotted line and the green dotted line were marked the main O-2p and Ni-3d orbital density of states, respectively. Effect of chlorine doping on redox mechanism To further explore the redox mechanism in chlorine doping LLOs, magnetic moment analysis was employed. Figure 7 shows the change of magnetic moment during charging process. In Li1.11-zNi0.89O2, the magnetic moment of Ni decreases from z=0 to z=0.7, after that, it



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remains unchanged. The magnetic moment of O does not change until z>0.7. That is to say, during the whole charging process, Ni ions participate in charge compensation from z=0 to z=0.7, while O ions involve redox reaction from z>0.7. This is corresponding to the two regions of charging curve in Li1.11-zNi0.89O2 (Figure 5d). The first region involves the Ni ion redox, while the second region is related to the oxygen redox. These two redox stages are consistent with reports about the charging process of Li-rich layered oxides.6

Figure 7. The change of magnetic moment on each atom during charging process of Li1.11zNi0.89O2

(a), Li1.11-zNi0.89O1.89Cl0.11 (b) and Li1.11-zNi0.89O1.78Cl0.22 (c). The dotted blue line

marked the starting point of oxygen redox reaction.


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In Li1.11-zNi0.89O1.89Cl0.11, the magnetic moment of Cl basically keeps unchanged during the whole delithiation process, implying that the small amount of chlorine doping do not involve in charge compensation. This is consistent with the above charge density differences analysis (Figure 3). From z=0 to z=0.8, the change of the magnetic moment mainly occurred in Ni ions. And the magnetic moment of O does not change until z>0.8. So in this system, Ni denotes more electrons and O contributes less electrons during charging, meaning that the first region with nickel redox activity would be expanded and the second region with oxygen redox become shorter. Similarly, to the Li1.11-zNi0.89O1.89Cl0.22, chlorine charge compensation could be neglected, and nickel redox reaction mainly occurred from z=0 to z=0.9. The length of oxygen redox further decreases. That means that chlorine doping tunes the length of redox couple reaction. Less anion oxygen involve charge compensation, which is favor of alleviating the oxygen evolution. In addition, voltage decay is also one of obstacles inhibiting the Li-rich cathode commercialization. Extensive works have been done to attack this problem, one of which is intelligently altering the composition through doping. Lee et al. suggested that decreasing the length of the oxygen redox plateau by increasing Ni content at the expense of the Li and Co content can reduce voltage decay.55 Song et al. proposed that Cr-doped Li-rich cathodes, associated with the reduction of Li2MnO3-like component, could suppress the voltage decay.56 Extending this idea of decreasing the length of the oxygen redox plateau in this work, it could be deduced that chlorine doping Li-rich cathode would also slow down the voltage decay. Table 2 gives the average redox potential of nickel and oxygen in Li1.11Ni0.89O2-yCly according to the calculated charging curves and the magnetic moment analysis. With the increasing chlorine content, the average redox potential of Ni ions slightly decreased from 3.93V



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to 3.87V, then to 3.82V. And the anion oxygen redox potential also declined from 4.66V to 4.51V. When chlorine doping amount increased to 0.22, the oxygen redox potential does not decrease further. This would because the O-2p orbital density states do not continue closer to the Fermi energy (Figure S6). Table 2. The average redox potential of nickel and oxygen redox couple in Li1.11Ni0.89O2-yCly according to the calculated charging curves and magnetic moment analysis. Cation Ni redox potential (V)

Anion O redox potential (V)

Li1.11Ni0.89O2

3.93

4.66

Li1.11Ni0.89O1.89Cl0.11

3.87

4.51

Li1.11Ni0.89O1.78Cl0.22

3.82

4.60

Rate performance The rate performance depends on the charge-transfer resistance of Li ion, which is related with the electrical conductivity and Li ion diffusion coefficient in LLOs. As shown from the total density of states (TDOS) in Li1.11Ni0.89O1.89Cl0.11 (Figure 8a), the band gap decreases when some oxygen was replaced with chlorine. Moreover, the TDOS is through the Fermi energy in Li1.11Ni0.89O1.78Cl0.22 (Figure S7). It suggests that the electrical conductivity would be enhanced due to chlorine substitution. For the lithium ion diffusion, we used the nudged elastic band (NEB) method to simulate the Li migration paths.57,

58

The possible Li migration paths and

diffusion barriers were given in Figure S8. The results show that chlorine doping improves the Li+ diffusion performance through decreasing the Li+ hop barrier along c direction (See Figure


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S8). On the other hand, because Ni2+ ion has the similar ionic radius with Li+ ion, layered oxides LiNiO2 usually suffers from the Li/Ni anti-site defects,59,

60

which severely hinder the Li+

migration, and result in a negative effect to rate performance. Therefore, we compared the difference of the defect formation energy of Li1.11Ni0.89O2-yCly (y=0, 0.11) with and without the Li+/Ni2+ anti-site defect. The structures with the anti-site defect are described in Figure S9. As shown in Figure

8b, the Li+/Ni2+ anti-site defect formation energy (0.5eV) in

Li1.11Ni0.89O1.89Cl0.11 is higher than that (0.35eV) in Li1.11Ni0.89O2, indicating that chlorine doping could prevent Ni2+ migrating into the Li layer and attenuate the defect formation. Simply put, chlorine doping is favorable for the enhancement of rate performance.

Figure 8. The total density of states in Li1.11Ni0.89O2-yCly (y=0, 0.11) (a); the Li+/Ni2+ mixing defect formation energy in Li1.11Ni0.89O2-yCly (y=0, 0.11) (b). CONCLUSION



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In the present work, we have examined the effect of chlorine doping on the stability, redox potential, redox mechanism and rate performance. After chlorine element is doped into the lithium-rich layered oxides, the charge potential decreases, the length of oxygen redox reaction shortens and rate performance is improved. These variations were beneficial for the modification of the safety, cycling stability and voltage decay of LLOs materials. This work not only provides new insight in deeper understanding the redox chemistry in anion-doped Li-rich cathode materials, but also provides a new approach of tuning the redox potential to improve the electrochemical performance of cathode.

ASSOCIATED CONTENT Suppoting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: The following files are available free of charge. The structures of Li1.11Ni0.89O2-yCly (y=0.22, 0.33, 0.44) and Li1.11Ni0.89O1.89A0.11 (A=F, Br); the valence state of each Ni atom in Li1.11Ni0.89O2-yCly (y=0, 0.11, 0.22); The average charge of each element in Li1.11Ni0.89O2-yCly and full delithiated Ni0.89O2-yCly through bader charge analysis; the whole charge density differences between Li1.11Ni0.89O2-yCly and Ni0.89O2-yCly; the optimized structure of Li1.11-zNi0.89O1.89Br0.11 (z=0.77); the O-2p and Ni-3d orbital density of states in Li1.11Ni0.89O2-yCly (y=0, 0.11, 0.22); the total density of states in Li1.11Ni0.89O1.78Cl0.22; the possible Li migration paths in Li1.11Ni0.89O2-yCly (y=0, 0.11) and the Li ion diffusion barrier of


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the corresponding each path; the structures with anti-site defect in Li1.11Ni0.89O2-yCly (y=0, 0.11); and the equations involved in the article. (PDF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by the new energy project for electric vehicle of national key research and development program (2016YFB0100200) and Nation Natural Science Foundation of China (51671004). The work was carried out at National Supercomputer Center in Tianjin, and the calculations were performed on TianHe-1(A). REFERENCES (1) Rossouw, M. H.; Liles, D. C.; Thackeray, M. M. Synthesis and Structural Characterization of a Novel Layered Lithium Manganese Oxide Li0.36Mn0.91O2 and its Lithiated Derivative Li1.09Mn0.91O2. J. Solid State Chem. 1993, 104, 464-466. (2) Lu, Z. H.; Beaulieu, L. Y.; Donaberger, R. A.; Thomas, C. L.; Dahn, J. R. Synthesis, Structure, and Electrochemical Behavior of Li[NixLi1/3-2x/3Mn2/3-x/3]O2. J. Electrochem. Soc. 2002, 149, A778-A791. (3) Kim S.; Cho W.; Zhang X.; Oshima Y.; Choi J. W. A Stable Lithium-Rich Surface Structure for Lithium-Rich Layered Cathode Materials. Nat. Commun. 2016, 7, 13598. (4) Li B.; Yan H.; Zuo Y.; Xia D. Tuning the Reversibility of Oxygen Redox in Lithium-Rich Layered Oxides. Chem. Mater. 2017, DOI: 10.1021/acs.chemmater.6b04743. (5) Feng X.; Gao Y.; Ben L.; Yang Z.; Wang Z.; Chen L. Enhanced Electrochemical Performance of Ti-doped Li1.2Mn0.54Co0.13Ni0.13O2 for Lithium-Ion Batteries. J. Power Sources 2016, 317, 74/ 26Environment ACS Paragon19 Plus


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First-Principles Study: Tuning the Redox Behavior of Lithium-Rich

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