Decoupling the effect of vacancies and electropositive cations on the anionic redox processes in Na based P2-type layered oxides

doi:10.1016/j.ensm.2020.05.032

Energy Storage Materials

Volume 31, October 2020, Pages 146-155

https://doi.org/10.1016/j.ensm.2020.05.032 Get rights and content

Highlights

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P2–Na_0.63[□_0.036Mg_0.143Mn_0.820]O₂ includes two sources of anionic redox activation.
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Characterizations show that both anionic redox sources act independently.
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Disordered vacancies lead to irreversible oxygen oxidation opposite to ordered ones.
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The oxidation of oxygen acts as structure stabilizer of the charged P2-type structure.

Abstract

The activation of anionic redox couple is recognized as one of the best way to increase the energy density of positive electrode materials in both Li and Na-ion batteries. However, for such hope, to materialize a better understanding of the parameters governing the activation, reversibility and efficiency of the anionic redox in NaMO₂ layered compounds is still sorely needed. Herein, we report a new P2–Na_0.63[□_0.036Mg_0.143Mn_0.820]O₂ compound that combines vacancies and Mg doping as well-known sources for anionic redox activation and benchmark its electrochemical performances against P2–Na_0.72[Mg_0.31Mn_0.69]O₂. We found that vacancies and Mg doping trigger independently anionic redox processes that differ in terms of redox voltage and reversibility. The one associated to vacancies occurs at the lowest potential and is irreversible. Moreover, we evidenced by monitoring the structural evolution of the pristine phase during cycling the benefice of anionic processes in ensuring the stabilization of P2-type structure at high voltage over a wide range in Na content. These findings highlight the importance of the anionic redox process origin (e.g. vacancies vs. highly electropositive cations) in governing the material electrochemical properties, while providing a new way to efficiently stabilize, without capacity loss, the P2-type structure through the charge process in non A-rich compounds.

Graphical abstract

Introduction

The activation of the anionic redox couple in Li based layered oxide is one of the best solution to improve the specific energy of the positive electrode materials [[1], [2], [3], [4]]. However, the practical application of such anionic redox is still limited either due to O₂ release or the cation migration associated with the oxygen redox activity [5]. In parallel, the Na-ion batteries are now recognized as one of the possibilities to replace, in dedicated range of application where gravimetric penalty is not a real concern, the LIBs and solve the issues of distribution of resources, cost and safety. The search for high energy density NIBs is then ongoing and the development of layered NaMO₂ compounds exhibiting cumulative cationic and anionic redox couples is investigated. Since the first evidence of anionic redox in the model Na-rich compound Na₂RuO₃ allowing to evidence that Na, as Li, can activate the anionic redox [6,7], the participation of non-bonding |O_2p states to the capacity has also been reported in Na-deficient Na_xMO₂, where the M sites are partially occupied by earth-alkaline (Mg) [8], vacancies [[9], [10], [11]] or more electronegative Zn ions [12]. Taking benefit, in the case of Na based layered oxides, of the wide possibility to tune chemical composition of the transition metal layer, we decided to investigate the effect of the combination of different species known to trigger oxygen oxidation on the behavior of anionic redox couple.

Anionic redox in AMO₂ layered oxides (A = Li, Na and M = transition metal) has been shown to arise from the occurrence of O(2p) non-bonding orbitals created by substituting part of the transition metal by species engaging ionic bonds with O so that electrons on these bonds are mainly localized on the oxygen anions. Among possibilities to activate anionic redox, vacancies in the transition metal sites are known to lead to whether reversible or irreversible anionic redox process when their distribution is respectively ordered [9] or disorder [11]. The absence of positive charge in the vacant site can be considered as leading to the limit situation where electrons are fully localized on oxygen anions and so that the corresponding non-bonding |O_2p states should present the highest energy. At the opposite, the +2 charge carried out by Mg or Zn species, both known to activate anionic redox, should bring the non-bonding |O_2p states deeper in energy, causing an energy difference with that of vacancies related one, large enough to be distinguishable. Mg and Zn doping being reported to lead to fully reversible anionic process and Mg showing, contrary to Zn, no cation migration along cycling, we decided to synthesize a mixed vacancy/Mg doped layered compound to study the effect of the combination of two sources for anionic redox activation on the overall electrochemical behavior. Most of anionic redox specificities such as efficiency, reversibility and structure changes being observable during the first activation of the process, the studies focus on the first charge/discharge behavior of model compounds P2–Na_2/3[Mn_1-y-zMg_y□_z]O₂ targeting Mn in not-active +4 valence state to minimize cationic redox contribution.

Here we show the successful synthesis of mixed vacancy/Mg layered oxide P2–Na_0.63[□_0.036Mg_0.143Mn_0.820]O₂ which exhibits two distinct oxygen redox activities both in terms of voltage and reversibility. The comparison of the electrochemical behavior with that of purely Mg doped P2– Na_0.72[Mg_0.31Mn_0.69]O₂ compound used as reference, allows attributing each process to the vacancy or Mg activated anionic redox couple and demonstrates that they act in an independent way. The investigation of structural changes during the first charge/discharge process allows confirming the benefit of anionic redox activation on the stabilization of the P2 structure at high state of charge with a clear postponement or even suppression of the P2 to O2 structure change. This stabilizing effect occurring while anionic redox is active allows maintaining capacity opposite to the loss observed when non-active element such as Al³⁺ are used to prevent access to high state of charges.

Section snippets

Material synthesis and chemical quantification

The series of Na_2/3Mg_yMn_1-yO₂ with y = 0.15, 0.2, 0.25, 0.3, 0.33 were prepared via solid state reaction between Na₂CO₃ (>99.5% Aldrich) with 5 wt% excess and stoichiometric amounts of (MgCO₃)₄ Mg(OH)₂·5H₂O (99.99% Aldrich) and Mn₃O₄ (>97%). The reactants were ball-milled altogether for 30min in SPEX-miller at 1725 rpm with r_ball/powder weight ratio of 7 and heat treated at 900 °C for 12h with the ramping rate of 5 °C/min. The cooling procedure adapted to allow creation of vacancies as

Structure and chemical composition analysis

The X-ray diffraction (XRD) patterns of the Na_2/3[Mg_yMn_1-y]O₂ samples with y = 0.15, 0.2, 0.25, 0.3, 0.33 reported in Fig. 1 and compared with calculated one using structure data reported by Delmas [17] show that all samples correspond to P2-type layered structure. The XRD pattern for sample with y = 0.33 shows extra peaks corresponding to MgO impurity which indicates that the limit of the solid solution domain is restricted to y = 0.3 in agreement with reported data [8,18]. Extra

Discussion

The comparative analysis of the studied compounds (y = 0.15 and y = 0.3) shows that despite they belong to the solid solution P2-Na_xMn_1-yMg_yO₂, the low Mg content compound exhibits vacancies in the transition metal oxide layer while no vacancies have been evidenced in the high Mg content compound. The latter is close to the already widely studied P2–Na_2/3Mg_0.28Mn_0.72O₂ [8,18] showing, among others, the activation of anionic redox corresponding, in the voltage curve, to a plateau at around

Conclusion

We compared two members of the same solid solution in which we can discriminate the effects, on the anionic redox, of different activation sources (vacancies, Mg²⁺) with the one associated to the cation vacancies occurring at lower voltage and being irreversible. We demonstrated the importance of the cation vacancies and Mg²⁺ distribution in ruling the reversibility of the anionic redox process with the process being irreversible when the vacancies are pinned to local structural distortion in a

CRediT authorship contribution statement

Xue Bai: Investigation, Writing - original draft. Antonella Iadecola: Investigation, Writing - original draft. Jean-Marie Tarascon: Supervision, Writing - review & editing. Patrick Rozier: Conceptualization, Writing - original draft, Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

X. B. thanks the French National network “Réseau sur le Stockage Electrochimique de l’Energie” (RS2E) FR CNRS 3459 and Agence Nationale de la Recherche (Label STORE-EX) for financial support. J.-M.T. acknowledge funding from the European Research Council (ERC) (FP/2014)/ERC Grant-Project 670116-ARPEMA. This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement 646433-Naïades. The authors also thank the synchrotron SOLEIL

References (31)

P. Rozier et al.
Anionic redox chemistry in Na-rich Na2Ru1 - YSnyO3 positive electrode material for Na-ion batteries
Electrochem. Commun.
(2015)
J.W. Murray et al.
The oxidation state of manganese in marine sediments and ferromanganese nodules
Geochem. Cosmochim. Acta
(1984)
R. Stoyanova et al.
Stabilization of over-stoichiometric Mn4+ in layered Na2/3MnO2
J. Solid State Chem.
(2010)
X. Rong et al.
Anionic redox reaction-induced high-capacity and low-strain cathode with suppressed phase transition
Joule
(2019)
M. Sathiya et al.
Reversible anionic redox chemistry in high-capacity layered-oxide electrodes
Nat. Mater.
(2013)
A. Grimaud et al.
Anionic redox processes for electrochemical devices
Nat. Mater.
(2016)
N. Yabuuchi
Solid-state redox reaction of oxide ions for rechargeable batteries
B. Li et al.
Anionic redox in rechargeable lithium batteries
Adv. Mater.
(2017)
G. Assat et al.
Fundamental understanding and practical challenges of anionic redox activity in Li-ion batteries
Nat. Energy
(2018)
B. Mortemard De Boisse et al.
Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode
Nat. Commun.
(2016)

U. Maitra et al.

Oxygen redox chemistry without excess alkali-metal ions in Na2/3[Mg0.28Mn0.72]O2

Nat. Chem.

(2018)

B. Mortemard de Boisse et al.

Highly reversible oxygen-redox chemistry at 4.1 V in Na4/7−x[□1/7Mn6/7]O2 (□: Mn vacancy)

Adv. Energy Mater

(2018)

Y. Li et al.

Native vacancy enhanced oxygen redox reversibility and structural robustness

Adv. Energy Mater.

(2019)

C. Ma et al.

Exploring oxygen activity in the high energy P2-type Na0.78Ni0.23Mn0.69O2 cathode material for Na-ion batteries

J. Am. Chem. Soc.

(2017)

X. Bai et al.

Anionic redox activity in a newly Zn-doped sodium layered oxide P2-Na2/3Mn1−yZnyO2 (0 < y < 0.23)

Adv. Energy Mater.

(2018)

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Citation Excerpt :
Meanwhile, the TM d-O 2p orbital interactions were strengthened and Fermi level was pinned at the top of O 2p state (see Fig. 6e and S11). Then, the O2−/O− anionic redox occurs with the further extracting of Na+ [52–54]. The pDOS evolution of NRO-Co0.1 is similar to that of NRO-Co0 (Fig. S11).
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Decoupling the effect of vacancies and electropositive cations on the anionic redox processes in Na based P2-type layered oxides

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Material synthesis and chemical quantification

Structure and chemical composition analysis

Discussion

Conclusion

CRediT authorship contribution statement

Declaration of competing interest

Acknowledgements

Electrochem. Commun.

Geochem. Cosmochim. Acta

J. Solid State Chem.

Joule

Reversible anionic redox chemistry in high-capacity layered-oxide electrodes

Nat. Mater.

Anionic redox processes for electrochemical devices

Nat. Mater.

Solid-state redox reaction of oxide ions for rechargeable batteries

Anionic redox in rechargeable lithium batteries

Adv. Mater.

Fundamental understanding and practical challenges of anionic redox activity in Li-ion batteries

Nat. Energy

Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode

Nat. Commun.

Oxygen redox chemistry without excess alkali-metal ions in Na2/3[Mg0.28Mn0.72]O2

Nat. Chem.

Highly reversible oxygen-redox chemistry at 4.1 V in Na4/7−x[□1/7Mn6/7]O2 (□: Mn vacancy)

Adv. Energy Mater

Native vacancy enhanced oxygen redox reversibility and structural robustness

Adv. Energy Mater.

Exploring oxygen activity in the high energy P2-type Na0.78Ni0.23Mn0.69O2 cathode material for Na-ion batteries

J. Am. Chem. Soc.

Anionic redox activity in a newly Zn-doped sodium layered oxide P2-Na2/3Mn1−yZnyO2 (0 < y < 0.23)

Adv. Energy Mater.