Electrolytic MnO2-Zn battery and electrolyte

Abstract

The invention provides an electrolytic MnO2-Zn battery and an electrolyte, and belongs to the technical field of electrochemical energy storage. The electrolytic MnO2-Zn battery comprises an electrolyte which is an acidic solution comprising zinc salt, manganese salt and rare earth metal salt; the positive electrode is used for carrying out redox reaction of Mn < 2 + > / MnO2 with the electrolyte; the negative electrode is used for carrying out Zn < 2 + > / Zn oxidation-reduction reaction with the electrolyte; rare earth metal ions of the rare earth metal salt serve as an active substance on the positive electrode and participate in the reaction together with Mn < 2 + > / MnO2.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to an electrolytic MnO2-Zn battery and an electrolyte. Background Art

[0002] Manganese (Mn)-based materials are expected to become large-scale electrode materials for the next generation of energy storage devices because manganese has multiple variable valence states and its redox properties can provide MnO2-Zn batteries with advantages such as high theoretical capacity, environmental friendliness, abundant resources and cost-effectiveness.

[0003] However, when MnO2 is used as the positive electrode for electrode reaction, it is difficult to avoid the disproportionation reaction of manganese ions caused by the Jahn-Teller effect. That is, when the manganese ion is trivalent, it is in a higher spin state, and the electron distribution on the d orbital is asymmetric, which causes the lattice structure around the manganese ion to deform, and eventually causes the MnO2 electrode to undergo a disproportionation reaction and decompose into different components. At the same time, the limited inherent conductivity of MnO2 hinders the complete reaction, resulting in lower charge / discharge efficiency, difficulty in achieving large load and high rate cycles, and rapid attenuation of battery life, thus hindering the development of manganese-based batteries. Summary of the invention

[0004] In view of this, in order to at least partially solve at least one of the above-mentioned technical problems, the present invention provides an electrolytic MnO2-Zn battery and an electrolyte.

[0005] According to an embodiment of one aspect of the present invention, an electrolytic MnO2-Zn battery is provided, comprising: an electrolyte, comprising an acidic solution of a zinc salt, a manganese salt and a rare earth metal salt; a positive electrode for reacting with the electrolyte to convert MnO2-Zn into 2+ / MnO2 redox reaction; negative electrode, used for Zn 2+ / Zn redox reaction; the rare earth metal ions of the rare earth metal salt act as active substances at the positive electrode and react with Mn 2+ / MnO2 participate in the reaction together.

[0006] According to an embodiment of the present invention, the rare earth metal ions include at least one of europium, cerium, holmium and gadolinium.

[0007] According to an embodiment of the present invention, the electrolyte further includes a pH adjusting solution, and the pH adjusting solution adjusts the pH of the electrolyte to 1.5-2.5.

[0008] According to an embodiment of the present invention, rare earth metal ions serve as supporting centers of the MnO2 structure, shielding the Mn 2+ During the oxidation process of MnO2 3+ Production of intermediates.

[0009] According to an embodiment of the present invention, the rare earth metal salt includes at least one of europium acetate, holmium acetate, cerium acetate, and gadolinium acetate.

[0010] According to an embodiment of the present invention, the concentration of the pH adjusting solution is 0.1-1 mol / L; the pH adjusting solution includes at least one of a sulfuric acid solution, a hydrochloric acid solution, and a nitric acid solution.

[0011] According to an embodiment of the present invention, the concentration of the manganese salt is 0.1-5 mol / L; the concentration of the zinc salt is 0.1-5 mol / L; and the concentration of the rare earth metal salt is 0.01-1 mol / L.

[0012] According to an embodiment of the present invention, the rare earth metal ions in the rare earth metal salt have a valence of +3.

[0013] According to an embodiment of the present invention, the zinc salt includes at least one of zinc sulfate, zinc chloride, zinc nitrate, zinc bromide and zinc acetate; the manganese salt includes at least one of manganese sulfate, manganese chloride, manganese nitrate, manganese bromide and manganese acetate.

[0014] According to another embodiment of the present invention, there is provided an electrolyte for the above-mentioned electrolytic MnO2-Zn battery.

[0015] According to the embodiments of the present invention, rare earth metals have relatively unique f orbitals and more electronic transition energy levels, which are easy to couple with similar energy levels of metal Mn. 2+ / MnO2 deposition and dissolution process, that is, through df double orbital hybrid coupling to reduce the multi-step conversion of the positive electrode reaction, to achieve a one-step conversion of double electron transfer, thereby promoting sufficient positive electrode reaction and improving the electrochemical performance of the electrolytic MnO2-Zn battery. The electrolytic MnO2-Zn battery of the present invention combines the MnO2 positive electrode regulated by rare earth metal ions with the zinc negative electrode, and the assembled electrolytic MnO2-Zn battery has excellent electrochemical performance, high battery capacity and rate performance, and still has high stability after multiple cycles.

[0016] Rare earth metal ion-regulated electrolytic MnO2-Zn batteries will help advance the development of higher energy and higher power density aqueous batteries, and help promote the practical application of the next generation of safe and low-cost grid-scale energy storage systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0018] Figure 1 The reaction mechanism diagram of rare earth metal ions regulating positive electrode MnO2 in an embodiment of the present invention is shown;

[0019] Figure 2 The europium ion-regulated Mn 2+ and Mn 4+ The partial wave state density distribution diagram of Mn d orbital and Eu f orbital before and after charging during the conversion process;

[0020] Figure 3 A crystal field analysis diagram showing the electronic structure of the d orbital of Mn and the f orbital of Eu during the charge and discharge process of Example 1 of the present invention;

[0021] Figure 4 The analysis spectra of the MnO2@Eu positive electrode of Example 1 of the present invention and the MnO2 of Comparative Example 1 are shown;

[0022] Figure 5 The performance diagrams of the MnO2@Eu positive electrode of Example 1 of the present invention and the MnO2 of Comparative Example 1 assembled into half-cells are shown;

[0023] Figure 6 The performance diagrams of the electrolytic MnO2@Eu-Zn battery 2 of Example 2 and the MnO2-Zn battery 2' of Comparative Example 2 are shown;

[0024] Figure 7 The performance diagram of the ampere-hour-level electrolytic MnO2@Eu-Zn large battery 3 of Example 3 and the ampere-hour-level MnO2-Zn large battery 3' of Comparative Example 3 is shown;

[0025] Figure 8 The current response and charge-discharge curves of the electrolytic MnO2@RE-Zn battery 4 of Example 4 (RE is Ce, Ho, Gd, respectively) and the MnO2-Zn battery 2' of Comparative Example 2 are shown. DETAILED DESCRIPTION

[0026] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0027] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The term "comprising" used herein indicates the existence of features, steps, operations, but does not exclude the existence or addition of one or more other features.

[0028] In the case of using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.). In the case of using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, or C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0029] In the present invention, the term "Jahn-Teller effect" refers to the 3+ ) leads to the disproportionation of MnO2. 3+ There are four electrons in the d orbital (d 4 configuration). In an octahedral coordination environment, these four electrons are distributed in the t2g and e9 orbitals. According to crystal field theory, in an ideally symmetric octahedral field, the t2g orbital is triply degenerate, while the e9 orbital is doubly degenerate. Specifically, Mn 3+ This causes the surrounding oxygen atoms to stretch outward, forming a slightly distorted octahedral structure. This deformation allows the electrons to redistribute to lower energy states. 3+ , the most commonly observed is the octahedron elongated along the z-axis (called elongation type distortion), because such deformation can best alleviate the degeneracy. 3+ The Jahn-Teller effect may lead to unstable material structure, thus affecting the electrochemical performance. For example, it may cause capacity decay, because the structural changes may make the insertion and extraction of zinc ions difficult, or directly cause the dissolution loss of active materials collected on the positive electrode material, thereby reducing the cycle stability and efficiency of electrolytic MnO2-Zn batteries.

[0030] Jahn-Teller effect and Mn 3+ The disproportionation reaction of ions usually leads to irreversible structural transformation and Mn 2+ / Mn 3 +Ion dissolution ultimately reduces the cycle stability of electrolytic MnO2-Zn batteries. The Jahn-Teller effect is indeed a challenging issue in battery materials, especially those lithium-ion batteries containing Mn metal. During the battery cycle, especially when the battery is charged and discharged, the injection and extraction of ions can easily lead to Jahn-Teller distortion of the crystal structure of Mn metal, ultimately leading to poor battery cycle stability and reduced capacity.

[0031] Manganese dioxide (MnO2) can undergo solid-state conversion and cation (i.e. Li + 、Zn 2+ 、Na + , H + ) embedded. It uses Mn 3+ and Mn 4+ The reversible valence transition between MnO2 and MnO2 facilitates large charge transfer and achieves high electrochemical potential, making MnO2 a typical cathode material with high energy density in secondary batteries.

[0032] The related technology of the present invention proposes an electrochemical method based on MnO2 electrolysis chemistry, which realizes the electrochemical reaction of solid MnO2 and liquid Mn 2+ This innovative approach can achieve 616 mAh g -1 The high theoretical capacity of MnO2 and the output voltage of about 1.23 V (verus SHE) show great promise for the design of high-performance manganese-based batteries suitable for large-scale energy storage applications. However, it was found in practice that the MnO2 accompanied by the Mn 3+ The Jahn-Teller effect causes a chemical disproportionation reaction, and the limited intrinsic conductivity of MnO2 hinders the complete electrolysis reaction, resulting in low charging and discharging efficiency of the prepared MnO2 battery, difficulty in achieving high-load and high-rate cycles, and rapid attenuation of the battery life, making it difficult to promote its application.

[0033] In the process of carrying out the present invention, it was found that in Mn 2+ In the process of oxidation to MnO2, due to the presence of Mn 3+ Intermediates, chemical disproportionation process will occur. Mn 3+ There are some inherent differences between the chemical disproportionation of the intermediate to produce chemical manganese dioxide (c-MnO2) and the in-situ electrodeposition to produce electrochemical manganese dioxide (e-MnO2). Although e-MnO2 can be reversibly deposited and dissolved, c-MnO2 is difficult to reversibly dissolve, which hinders the improvement of the MnO2 positive electrode capacity. In addition, due to the Mn 3+ The Jahn-Teller effect leads to the 3+Chemical disproportionation of ions and Mn 3+ The physical residue of ions in the electrolyte makes some Mn 3+ ions dissolve into the electrolyte, while the remaining Mn 3+ The ions are oxidized to MnO2 solid and deposited on the positive electrode or reduced to Mn 2+ Ions return to the electrolyte, reducing the cycle stability of electrolytic MnO2-Zn batteries.

[0034] In order to solve the above problems, the present invention adds rare earth metal ions into the electrolyte, utilizes the unique f orbital and more electron transition energy levels of rare earth metal ions, and more easily couples with the similar energy level (d orbital) of metal Mn, and shields Mn through df double orbital hybrid coupling. 3+ The generation of intermediates reduces the multi-step transformation of electrode reactions, realizes the one-step transformation of double electron transfer, and promotes sufficient electrode reactions.

[0035] Specifically, according to an embodiment of one aspect of the present invention, an electrolytic MnO2-Zn battery is provided, comprising: an electrolyte, comprising an acidic solution of zinc salt, manganese salt and rare earth metal salt; a positive electrode for reacting with the electrolyte to react with Mn 2+ / MnO2 redox reaction; negative electrode, used for Zn 2+ / Zn redox reaction; wherein the rare earth metal ions of the rare earth metal salt act as active substances at the positive electrode and react with Mn 2+ / MnO2 participate in the reaction together.

[0036] According to an embodiment of the present invention, rare earth metal ions are added to the electrolyte to provide f orbital electrons, thereby further adjusting the Mn 2+ / MnO2 deposition and dissolution electrochemical process, shielding Mn 3+ The generation of ions reduces the multi-step transformation of the electrode reaction, realizes the one-step transformation of double electron transfer, promotes the electrode reaction to be sufficient, and thus further improves the electrochemical performance of the electrolytic MnO2-Zn battery.

[0037] The above contents will be described in detail below.

[0038] The present invention uses rare earth metal ions (RE) as active materials in the positive electrode to participate in the reaction of the positive electrode. During charging, the positive electrode is composed of Mn ions that are easily soluble in water. 2+ ions are deposited into solid MnO2, and the negative electrode is composed of Zn 2+ The ions are reduced to solid metal Zn, and both the positive and negative active materials form solid phase materials. During discharge, the positive electrode dissolves Mn from solid MnO2. 2+ Ions, the negative electrode is made of solid metal Zn dissolving Zn 2+ Ions, dissolved Mn 2+and Zn 2+ The ions return to the electrolyte, and both the positive and negative active materials form a liquid phase.

[0039] It can be understood that the f orbital of rare earth metal ions is not full of electrons, has more active electrons and more electron transition energy levels, and is easy to combine with metal Mn with similar energy levels (Mn d orbital), and can be selected as a suitable regulator of MnO2 orbital hybrid coupling and energy band structure. The presence of rare earth metal ions can reduce Mn 2+ Ion to Mn 3+ ions, promoting the Mn 2+ Ion to Mn 4+ ions. The redox reaction of rare earth metal ions can react with Mn 2+ / MnO2 reaction coupling helps to improve the theoretical capacity of the electrode reaction. In addition, the use of electrolytes adjusted by rare earth metal ions helps to stabilize the structure of MnO2 and improve the conductivity of the battery structure, and effectively reduce or even shield Mn 3+ ions, thus helping to reduce Mn 3+ Ion disproportionation reaction and Mn in electrolyte 3+ The physical residue of ions makes the assembled MnO2@RE-Zn battery (which can be understood as the electrolytic MnO2-Zn battery of the present invention) show high surface capacity loading, high efficiency and long cycle life.

[0040] In the process of screening the metal ions added to the electrolyte, it was found that if transition metal ions are added to the electrolyte, it is difficult for the transition metal ions to interact with Mn because they do not have unfilled f electron orbitals. And when organic solvents are used as electrolytes, safety issues may also arise. The addition of rare earth metal ions can firstly increase the theoretical capacity of MnO2 intrinsically. In addition, due to the transfer of an f electron in the rare earth metal ions, a new f orbital charge storage energy level is introduced, which increases the energy injection of rare earth metal ions in the theoretical capacity of MnO2, thereby increasing the surface capacity load of the MnO2@RE-Zn battery.

[0041] It should be noted that the electrolytic MnO2-Zn battery of the present invention avoids the use of a diaphragm, can effectively avoid the high cost caused by the diaphragm, and saves the production time of the battery, and the electrolyte used is a single solution system, which further simplifies the battery preparation process. The positive and negative electrodes of the battery both use current collectors, and the active material comes from the electrolyte. The positive electrode can use carbon felt or carbon cloth as the current collector as needed, and the negative electrode uses zinc metal as the current collector, which avoids the complicated electrode preparation process and saves the production cycle and production cost of the battery.

[0042] According to the embodiment of the present invention, the electrolyte of the electrolytic MnO2-Zn battery optimized by rare earth metal ions is an aqueous electrolyte, which is non-toxic, harmless, non-flammable, and has high safety performance.

[0043] According to an embodiment of the present invention, the rare earth metal ions in the rare earth metal salt have a valence of +3.

[0044] The working principle of the charge and discharge process of electrolytic MnO2-Zn battery is as follows:

[0045] While charging:

[0046] Positive electrode: Mn 2+ +RE 3+ +2H2O-3e - →RE 4+ -MnO2+4H + ;

[0047] Negative electrode: Zn 2+ +2e - →Zn.

[0048] When discharging:

[0049] Positive electrode: RE 4+ -MnO2+4H + →Mn 2+ +RE 3+ +2H2O-3e - ;

[0050] Negative electrode: Zn → Zn 2+ +2e - .

[0051] When the rare earth metal in the rare earth metal salt is +3 valence, by 3+ and RE 4+ The redox reaction between 2 + / MnO2 reaction coupling, improve the theoretical capacity of the electrode reaction, and is more conducive to reducing Mn 3+ ions, thereby reducing Mn 3+ The disproportionation reaction of ions reduces the Jahn-Teller effect. The electrode reaction principle of the electrolytic MnO2-Zn battery of the present invention is that the positive electrode MnO2 / Mn 2+ and negative electrode Zn 2+ The dual deposition / dissolution mechanism of Mn / Zn further avoids the diffusion, migration and phase transformation of Mn ions within the crystal structure of the electrode material.

[0052] According to an embodiment of the present invention, the rare earth metal ions include at least one of europium (Eu), cerium (Ce), holmium (Ho), and gadolinium (Gd). In the process of conducting relevant experiments of the present invention, it was found that the above rare earth metal ions can participate in the positive electrode Mn 2+ In the process of the redox reaction of / MnO2, the electrons on the f orbital of the rare earth metal ion are coupled with the d orbital electrons of the metal Mn to realize the Mn 2+ / Mn 4+ One-step transformation of two-electron reaction, shielding Mn 3+ ions, promoting the production of Mn 2+ / MnO2 deposition and dissolution process, so that the electrolytic MnO2-Zn battery can be highly reversible and long-term cycle at high surface capacity. It should be noted that the above-mentioned rare earth metal ions of the present invention are only used as examples, and the unique f orbital electrons of other rare earth metal ions can also couple with the d orbital electrons of metal Mn, so that the electrolytic MnO2-Zn battery has a higher theoretical capacity.

[0053] According to an embodiment of the present invention, the electrolyte further comprises a pH adjusting solution, and the pH adjusting solution adjusts the pH of the electrolyte to 1.5-2.5, for example, 1.5, 2 or 2.5. It should be noted that, in the process of conducting experiments related to the present invention, it was found that when rare earth metal salts were added to the electrolyte and the pH was adjusted to acidic, for example, when the pH was above 3, the Mn 3+ However, it cannot completely shield Mn 3+ ions are generated, and some Mn 3+ When the pH is adjusted to 1.5-2.5, the Mn ions can be shielded by the synergistic effect of pH regulation and rare earth metal ions. 3+ , promoting Mn 2+ / MnO2 deposition and dissolution process, promotes the 2+ and Mn 4+ The direct double electron transfer reaction path between the two makes the electrolytic MnO2-Zn battery able to perform highly reversible and long-term cycles at high surface capacity. The present invention uses the f electrons of rare earth metal ions and the coordinated regulation of pH to shield Mn 3+ ions to promote Mn 2+ The one-step conversion of / MnO2 electrochemically provides an innovative approach to developing high-performance aqueous batteries for large-scale energy storage applications.

[0054] Preferably, the concentration of the pH adjusting solution is 0.1~1 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L, preferably 0.1 mol / L; the pH adjusting solution includes at least one of sulfuric acid solution, hydrochloric acid solution, and nitric acid solution, preferably sulfuric acid solution.

[0055] Figure 1 The reaction mechanism diagram of rare earth metal ions regulating positive electrode MnO2 in an embodiment of the present invention is shown, as Figure 1 As shown, rare earth metal ions act as supporting centers of the MnO2 structure, shielding the Mn 2+ During the oxidation process of MnO2 3+ In the MnO6 octahedral configuration, the O in the z-axis direction is defined as O I Type, O on the xy plane is defined as O II Type. In Mn 2+ &RE 3+ In the complex structure, two congruent triangle structures (Mn-O I -Ru-O II ), the structure is very stable and Mn-O I The bond length and Mn-O II The bonds are of the same length. This will result in Mn 2+ The ion can obtain two electrons at the same time during oxidation, that is, a direct double electron transfer reaction is achieved to maintain its approximately regular octahedral configuration and oxidize to Mn 4+ ions. At the same time, rare earth atoms can serve as the supporting center of the MnO2 crystal structure, making the MnO2 structure more stable. In the electrolyte system regulated by rare earth metal ions (Eu, Ce, Ho, Gd), trivalent rare earth metal ions (RE 3+ ) can be combined with Mn 2+ The fan-shaped MnO6 is formed by coupling the square REO4 as the supporting center and the MnO6 octahedral configuration. 2+ & RE 3+ Complex structure. This complex structure can rivet Mn 2+ ion in the MnO6 octahedron with one O atom along the Z axis and one O atom along the xy plane. This will result in Mn 2+ When the ion is oxidized, the MnO6 octahedron will not be highly distorted but will maintain a nearly octahedral configuration, so it is easier to convert into a nearly octahedral Mn 4+ions. The above conversion process results in the battery directly converting Mn into 2+ ions into Mn 4+ ions, in a specific range of pH 1.5~2.5, directly shield Mn 3+ ions, reducing the complex intermediate reaction process and realizing the one-step conversion of the double electron transfer reaction. At the same time, the redox reaction of the rare earth metal ions coupled with the Mn ions (RE 3+ With RE 4+ The presence of a small amount of electrolyte (between ions) also provides additional electron transfer for the electrode reaction, thereby providing additional capacity for the battery.

[0056] Understandably, Mn 2+ Ions and Mn 4+ The transformation between ions actually takes place in the MnO6 octahedral configuration, which is the crystal structure required in the crystal formation process.

[0057] According to an embodiment of the present invention, the rare earth metal salt includes at least one of europium acetate, holmium acetate, cerium acetate, and gadolinium acetate. The above rare earth metal salt has good solubility in the aqueous electrolyte and is relatively cheap. At the same time, the above acetate is a kind of weak acid and will not have a significant impact on the pH of the electrolyte, which is more conducive to achieving pH control of the electrolyte together with the pH regulating solution.

[0058] According to an embodiment of the present invention, the concentration of manganese salt is 0.1~5 mol / L, for example, it can be 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L; the concentration of zinc salt is 0.1~5 mol / L, for example, it can be 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L; the concentration of rare earth metal salt is 0.01~1 mol / L, for example, it can be 0.01mol / L, 0.05 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.41 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L, preferably 0.09 mol / L. The concentrations of the above materials are adjusted within the above ranges to promote the rare earth metal ions to fully participate in the Mn 2+ / MnO2, so that the f orbital electrons of rare earth metal ions interact with the d orbital of Mn ions, further shielding Mn 2+ / MnO2 conversion process 3+ ions, thus avoiding the Jahn-Teller effect.

[0059] Optionally, the zinc salt includes at least one of zinc sulfate, zinc chloride, zinc nitrate, zinc bromide, and zinc acetate; the manganese salt includes at least one of manganese sulfate, manganese chloride, manganese nitrate, manganese bromide, and manganese acetate. When the zinc salt and the manganese salt are selected from the above materials, they can have high solubility in the aqueous electrolyte, and are consistent with the acid radical of the pH regulating solution or the rare earth metal salt, without introducing other impurities, and avoiding unnecessary effects on the redox process.

[0060] According to another embodiment of the present invention, there is provided an electrolyte for the above-mentioned electrolytic MnO2-Zn battery.

[0061] According to an embodiment of the present invention, the zinc ions in the zinc salt in the electrolyte participate in the Zn 2+ / Zn redox reaction; manganese ions in manganese salts participate in the Mn 2+ / MnO2 redox reaction, the f orbital electrons of rare earth metal ions and the d orbital electrons of Mn double coupling, realize the Mn 2+ / Mn 4+ One-step transformation of two-electron reaction, shielding Mn 3+ ions, promoting the generation of MnO2 / Mn 2+ The above electrolyte can improve the theoretical capacity of electrolytic MnO2-Zn batteries, increase the energy density of batteries, help maintain the structural integrity of positive electrode materials, reduce the dissolution loss of positive electrode active materials, and extend the cycle life of batteries. In addition, rare earth metal ions can form a conductive network, promote the transmission of electrons, reduce interface resistance, help increase the charge and discharge rate of batteries, and improve rate performance.

[0062] According to an embodiment of another aspect of the present invention, a method for assembling an electrolytic MnO2-Zn battery is provided, wherein zinc salt, manganese salt, rare earth metal salt and pH adjusting solution are mixed to prepare an electrolyte; carbon felt or carbon cloth is used as a positive electrode, and zinc or zinc alloy is used as a negative electrode to assemble an electrolytic MnO2-Zn battery.

[0063] According to an embodiment of the present invention, rare earth metal ions are introduced into the electrolyte so that double coupling is formed between the f orbital electrons of the rare earth metal ions and the d orbital electrons of the Mn ions, thereby achieving the Mn 2+ / Mn 4+One-step conversion of the two-electron reaction avoids the Mn 3+ The generation of ions reduces the Jahn-Teller effect.

[0064] It should be noted that the single cell capacity of the electrolytic MnO2-Zn battery assembled in the present invention is as high as 12 mAh / cm 2 , rate performance up to 8 C, energy density of about 182 Wh / cm 2 , reaching more than 80 Wh / kg, and remaining stable after more than 1000 cycles. The production cost of the electrolytic MnO2-Zn battery of the present invention is controlled below US$10 per kilowatt-hour, thereby increasing its application potential and promotion value in the field of large-scale energy storage.

[0065] The present invention is further described below by embodiments and related test experiments and results thereof. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, it is obvious that one or more embodiments may also be implemented without these specific details. And, in the absence of conflict, the details in the following embodiments may be combined into other feasible embodiments at will.

[0066] It should be noted that the following specific examples are only for illustration, and the protection scope of the present invention is not limited thereto. The chemicals and raw materials used in the following examples are all commercially available or homemade by recognized processing methods.

[0067] Embodiment 1:

[0068] Assembly process of MnO2@Eu half-cell 1:

[0069] Carbon felt was used as the working electrode, platinum foil as the counter electrode, Ag / AgCl as the reference electrode, and a mixed solution of 1 M MnSO4, 0.1 M H2SO4, and 0.09 M europium acetate was used as the electrolyte. The 3D structure of carbon felt can provide an effective electrolyte contact reaction channel for the deposition and stripping of MnO2, and assemble to form a MnO2@Eu half-cell 1.

[0070] Figure 2 The europium ion-regulated Mn 2+ and Mn 4+ The partial wave state density distribution diagram of Mn d orbital and Eu f orbital before and after charging during the conversion process. Figure 2 As shown, it shows that there is a strong interaction between d orbitals and f orbitals. 2+ &Eu 3+ and Mn 3+ &Eu 4+ Mn-dz in the composite configuration2 and Eu-fz(x 2 -y 2 ) orbital, the energy distribution area and position of each energy level peak are consistent, which indicates that the Mn-dz 2 Energy levels and Eu-fz(x 2 -y 2 ) orbitals are hybrid coupled. And Mn-dx 2 -y 2 and Eu-fz 3 The energy distribution area of ​​the orbital and the position of each energy level peak are also consistent, revealing that the Mn-dx 2 -y 2 and Eu-fz 3 The orbitals are also hybrid coupled. 2 -y 2 &fz 3 and dz 2 &fz(x 2 -y 2 )) is beneficial to the Mn-dx 2 -y 2 and Mn-dz 2 The simultaneous electron conversion of the orbital is beneficial to promote the direct double electron transfer reaction of Mn ions and promote the 2+ and Mn 4+ direct conversion between .

[0071] Figure 3 The crystal field analysis diagram of the electronic structure of the d orbital of Mn and the f orbital of Eu during the charge and discharge process of Example 1 of the present invention is shown. Figure 3 As shown, Mn 2+ Ion d orbitals and Eu 3+ The f orbitals of ions are easily coupled due to their similar energy levels. 2+ &Eu 3+ There are two sets of orbital hybrid couplings between the composite configurations, namely dz 2 &fz(x 2 -y 2 ) and dx 2 -y 2 &fz 3 Orbital hybrid coupling. Although in Eu 3+ The ions are oxidized to Eu 4+ In the process of ions, Eu-fz 3 The orbital energy level loses an electron. However, due to the interaction between the orbital energy levels of Eu-f electrons, Eu-fz 3 The orbital energy level position does not rise. Under the interaction between the Eu-f electron orbital energy levels, Eu-fz(x2 -y 2 ) orbital energy level is significantly increased. 2 -y 2 The orbital energy level is related to Eu-fz 3 Orbital energy levels are coupled without rising, Mn-dz 2 The orbital energy level is related to Eu-fz(x 2 -y 2 ) orbital energy level coupling increases significantly. 2+ ions are oxidized to Mn 4+ In the process of ions, Mn-dx 2 -y 2 Orbital Energy Levels and Mn-dz 2 Each orbital energy level loses one electron, achieving a one-step transformation of double electron transfer. 4+ Reduced to Mn 2+ During the ion period, Mn-dx 2 -y 2 The orbital energy level of Eu-fz(x 2 -y 2 ) changes with the position of the orbital energy level, while Mn-dz 2 The orbital energy level of Eu-fz(x 2 -y 2 )'s orbital energy level decreases.

[0072] Comparative Example 1:

[0073] Assembly process of MnO2 half-cell 1':

[0074] The assembly process of this comparative example 1 is substantially the same as that of the embodiment 1, except that no rare earth metal ions are added in this comparative example 1 to assemble and form the MnO2 half-cell 1'.

[0075] Figure 4 The analysis spectra of the MnO2@Eu positive electrode of Example 1 of the present invention and the MnO2 of Comparative Example 1 are shown, wherein a is the X-ray diffraction analysis spectrum of the MnO2@Eu positive electrode and MnO2, b is the photoluminescence spectrum of the MnO2@Eu positive electrode and MnO2 at an excitation wavelength of 532 nm, c is the normalized Mn X-ray absorption spectrum (K-edge XANES spectrum) of the MnO2@Eu positive electrode and the MnO2 samples, wherein Mn foil, Mn2O3 and MnO2 are used as reference standards, and d is a linear fitting curve diagram of the Mn valence state in the electrode active material deposited on the carbon felt. Figure 4The XRD phase structure analysis in a in the figure reveals that the deposited MnO2 cathode is a tetragonal α-MnO2 phase with a tunnel structure, with a JPCDS number of 44-141. The XRD peak of the MnO2@Eu cathode shows a shift toward the low-angle direction, revealing the lattice expansion phenomenon. This phenomenon is caused by the change in local spacing after the introduction of Eu atoms into the MnO2 cathode. Figure 4 Figure b shows that the MnO2 cathode has no fluorescence peak in the wavelength range of 570-650 nm, while the MnO2@Eu cathode shows three different fluorescence peaks. The peak of the MnO2@Eu cathode at 579.5 nm corresponds to Eu 3+ Ionic 5 D0- 7 The broad peak with two split peaks between 590 and 600 nm is attributed to 5 D0- 7 The magnetic dipole transition (MDT) of F1 is an intrinsic parity-allowed transition that is independent of positional symmetry. The peak centered at about 617 nm comes from 5 D0- 7 The electric dipole transition (EDT) of F2, which is a kind of 3+ The intensity of the EDT fluorescence peak is higher than that of the MDT peak, which indicates that a small amount of Eu 3+ The ions occupy central symmetric positions within the MnO2 host lattice, which is consistent with the theoretical simulation of the high-symmetry center occupation of Eu atoms in the MnO2 structure.

[0076] like Figure 4 c~ Figure 4 As shown in (d), the K-edge curve of Mn in the deposited MnO2 is close to that of the Mn2O3 standard sample, indicating that the average valence state of Mn is close to trivalent. However, the Mn K-edge curve in the MnO2@Eu sample is closer to the MnO2 standard sample, indicating that the average valence state of Mn in the deposited MnO2@Eu is closer to tetravalent. The linear fitting of the Mn K-edge XAFS absorption spectrum reveals a significantly higher average Mn valence state (4.98) in the deposited MnO2@Eu compared to the average valence state of Mn in MnO2 (3.33), indicating that Eu ion regulation is beneficial to promote Mn oxidation.

[0077] The assembled MnO2@Eu half-cell and MnO2 half-cell were electrochemically tested respectively. Figure 5The performance graphs of the MnO2@Eu positive electrode of Example 1 of the present invention and the MnO2 of Comparative Example 1 assembled into half-cells are shown, wherein a is a curve of the voltage change over time of the MnO2@Eu half-cell and the MnO2 half-cell under a constant current charge of 12 mA, b is a charge and discharge curve of the MnO2@Eu half-cell and the MnO2 half-cell at 1 C and 8 C rates, respectively, and c is a comparison of the rate performance of the MnO2@Eu half-cell and the MnO2 half-cell. Figure 5 As shown in a, during constant current charging, the voltage of the MnO2 electrode of Comparative Example 1 first slowly increases to 1.08 V, and then tends to stabilize as the charging time increases. This process is accompanied by the 3+ The disproportionation of ions leads to incomplete deposition of the MnO2 cathode. However, the voltage of the MnO2@Eu cathode remains stable at around 1.1 V with the charging time. The voltage of the MnO2@Eu cathode is stable and higher than that of the Mn 3+ ions, indicating that the regulation strategy of Eu ions can promote the deposition of Mn 2+ ions are directly deposited as MnO2, thus effectively shielding Mn 3+ Ion generation. Charged to 12 mAh / cm at a constant current of 12 mA 2 Under the area capacity of MnO2, the voltage curve of the MnO2 electrode in Comparative Example 1 shows an upward trend, which reveals that the deposition process of the MnO2 electrode has undergone a 2+ →Mn 3+ →Mn 4+ However, the voltage curve of the MnO2@Eu cathode quickly reaches about 1.1 V at the initial stage of charging and then remains stable, indicating that the deposition process of the MnO2 electrode only undergoes the 2+ →Mn 4+ The double electron transfer process avoids the 2+ →Mn 3+ and Mn 3+ →Mn 4+ The single electron transfer process is realized, thus avoiding the Jahn-Teller effect.

[0078] like Figure 5 As shown in Fig. 2b, although both MnO2 half-cell 1′ and MnO2@Eu half-cell 1 show a high discharge platform of about 1.01 V at a discharge rate of 1 C, the MnO2 half-cell 1′ has a high discharge platform of about 10.62 mAh / cm 2 In comparison, the MnO2@Eu half-cell exhibits a significantly higher discharge capacity of 11.43 mAh / cm 2Even at a high rate of 8 C, the MnO2@Eu half-cell 1 still maintains a high discharge platform of 0.84 V and a Coulombic efficiency of 82.2%, which is superior to the lower Coulombic efficiency of 71.4% and a lower discharge platform of 0.73 V of the MnO2 half-cell 1'.

[0079] like Figure 5 As shown in Figure c, with the increase of discharge rate, the coulombic efficiency and energy density of MnO2@Eu half-cell 1 gradually decrease. When the discharge rate is restored to 1C, the MnO2@Eu half-cell 1 can recover to about 95.49% of the initial coulombic efficiency and about 93.54 Wh / m 2 Compared with the MnO2 half-cell 1', the MnO2@Eu half-cell 1 exhibits higher energy density and coulombic efficiency at high current density, which indicates that Eu in the electrolyte not only expands the capacity of MnO2 but also enhances its rate performance.

[0080] Embodiment 2:

[0081] Assembly process of electrolytic MnO2@Eu-Zn battery 2:

[0082] Carbon felt was used as the positive electrode, zinc as the negative electrode, and a mixed solution of 1 M MnSO4, 1 M ZnSO4, 0.1 M H2SO4, and 0.09 M europium acetate was used as the electrolyte to assemble an electrolytic MnO2@Eu-Zn battery 2.

[0083] Comparative Example 2:

[0084] Assembly process of MnO2-Zn battery 2':

[0085] The assembly process of this comparative example 2 is substantially the same as that of the embodiment 2, except that no rare earth metal ions are added in this comparative example 2 to form the MnO2-Zn battery 2'.

[0086] Electrochemical tests were performed on the assembled electrolytic MnO2@Eu-Zn battery 2 and MnO2-Zn battery 2', respectively.

[0087] Figure 6 Performance graphs of the electrolytic MnO2@Eu-Zn battery 2 of Example 2 and the MnO2-Zn battery 2' of Comparative Example 2 are shown, wherein a is a charge and discharge curve graph of the MnO2-Zn battery 2' at different rates, b is a charge and discharge curve graph of the electrolytic MnO2@Eu-Zn battery 2 at different rates, c is a comparison graph of the discharge capacity and discharge medium voltage of the two batteries at 1 C and 8 C rates, and d is a comparison graph of the cycle performance of the two batteries.

[0088] like Figure 6As shown in a, b, and c, as the discharge current increases, the discharge capacity and voltage platform gradually decrease. Compared with MnO2-Zn battery 2', the electrolytic MnO2@Eu-Zn battery 2 increases by 1.01 mAh / cm at 1 C rate. 2 The discharge capacity of the battery was increased by 1.1 mAh / cm at a discharge rate of 8 C. 2 and increase the discharge voltage to 0.32 V. Figure 6 As shown in (d), the MnO2-Zn battery 2' only maintains about 158 ​​Wh / m after 400 cycles. 2 of power and stopped working after 500 cycles, while the electrolytic MnO2@Eu-Zn battery 2 was able to undergo long cycles and could still be used after 1000 cycles.

[0089] Embodiment 3:

[0090] Assembly process of the ampere-hour MnO2@Eu-Zn large battery 3:

[0091] In order to further explore the practical application of electrolytic MnO2@Eu-Zn and its potential in large-scale energy storage, the electrodes and separators (area of ​​about 70 cm 2 ) were placed alternately to assemble an ampere-hour-level MnO2@Eu-Zn large battery 3 with a large capacity of 1.2 Ah.

[0092] Comparative Example 3:

[0093] Assembly process of the ampere-hour-class MnO2-Zn large battery 3':

[0094] The assembly process of this comparative example 3 is substantially the same as that of the embodiment 3, except that no rare earth metal ions are added in this comparative example 3 to form an ampere-hour-level MnO2-Zn large battery 3'.

[0095] Figure 7 The performance diagrams of the ampere-hour-level electrolytic MnO2@Eu-Zn large battery 3 of Example 3 and the ampere-hour-level MnO2-Zn large battery 3' of Comparative Example 3 are shown, wherein a is a test diagram of the ampere-hour-level electrolytic MnO2@Eu-Zn large battery 3 lighting an LED lamp, b is a charge and discharge curve diagram of the ampere-hour-level electrolytic MnO2@Eu-Zn large battery 3, and c is a cycle performance diagram of the ampere-hour-level MnO2-Zn large battery 3' and the ampere-hour-level electrolytic MnO2@Eu-Zn large battery 3.

[0096] like Figure 7 As shown in a, the charged MnO2@Eu-Zn large battery 3 can light up the "Mn-Zn" lamp composed of 66 diodes in a full parallel circuit. Figure 7As shown in b, the MnO2@Eu-Zn large battery 3 was charged to a capacity of 1.2 Ah at a constant voltage of 2.2 V and then discharged. The ampere-hour-level MnO2@Eu-Zn large battery 3 exhibited a discharge capacity of about 975 mAh and a discharge platform of about 1.9 V at 1 C, a discharge capacity of about 850 mAh and a discharge platform of about 1.78 V at 4 C, and a discharge capacity of about 620 mAh and a discharge platform of about 1.60 V at 8C. Figure 7 As shown in c, the high-capacity MnO2@Eu-Zn large battery 3 exhibits good cycling performance. It maintains a high energy density of about 92 Wh / kg at 1 C, which is almost twice the energy density of the largest capacity lead-acid battery (~50 Wh / kg), and even maintains an energy density of up to 80 Wh / kg at 8 C. The excellent performance of this electrolytic MnO2@Eu-Zn large battery 3 will help advance the development of high-energy, high-power density aqueous batteries and promote the practical application of the next generation of safe, low-cost grid-scale energy storage systems.

[0097] Embodiment 4:

[0098] Assembly process of electrolytic MnO2@RE-Zn battery 4 (RE are Ce, Ho, Gd respectively):

[0099] The assembly process of this embodiment 4 is substantially the same as that of embodiment 2, except that europium acetate is replaced with holmium acetate, cerium acetate, and gadolinium acetate, respectively, to form an electrolytic MnO2@RE-Zn battery 4.

[0100] Electrochemical tests were performed on the electrolytic MnO2@RE-Zn battery 4 assembled in Example 4 and the MnO2-Zn battery 2' in Comparative Example 2.

[0101] Figure 8 The current response and charge-discharge curve diagram of the electrolytic MnO2@RE-Zn battery 4 (RE are Ce, Ho, Gd, respectively) of Example 4 and the MnO2-Zn battery 2' of Comparative Example 2 are shown, wherein a is the current response diagram of the electrolytic MnO2@RE-Zn battery 4 (RE are Ce, Ho, Gd, respectively) of Example 4 and the MnO2-Zn battery 2' of Comparative Example 2, b is the charge-discharge curve diagram of the two batteries, and c is the long cycle performance diagram of the electrolytic MnO2@RE-Zn battery 4 (RE are Ce, Ho, Gd, respectively) of Example 4.

[0102] like Figure 8 As shown in a, compared with MnO2-Zn battery 2', electrolytic MnO2@RE-Zn battery 4 has a higher charge efficiency than MnO2-Zn battery 2' when charged to 12 mAh / cm 2 The charge current response at the surface capacity is improved by about 10 mAcm -2, the charging time is shortened by about 15 minutes. Figure 8 As shown in (b), the discharge curves of electrolytic MnO2@RE-Zn battery 4 regulated by different rare earth metal ions (Ce, Ho, Gd) show a flat discharge platform around 1.95 V and a peak current of about 11.2 mAh / cm 2 In contrast, the discharge curve of MnO2-Zn battery 2' shows a discharge platform at only 1.93 V and a high discharge capacity at 12 mAh / cm 2 The charge capacity is only 10.15 mAh / cm 2 Low discharge capacity. Figure 8 As shown in Figure c, the coulombic efficiency and energy density of the electrolytic MnO2@RE-Zn battery 4 optimized by rare earth metal ions (Ce, Ho, Gd) at a discharge rate of 1C exceeded 90% and 175 Wh / m 2 The rare earth metal ion optimized electrolytic MnO2@RE-Zn battery 4 assembled in this embodiment 4 has stable high energy density, high coulombic efficiency and long cycle stability, highlighting the efficacy of the rare earth metal ion regulation strategy.

[0103] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An electrolytic MnO2-Zn battery, comprising: an electrolyte, including an acidic solution of a zinc salt, a manganese salt, and a rare earth metal salt; Positive electrode, used for conducting Mn with the electrolyte 2+ / Redox reaction of MnO2; A negative electrode for conducting Zn 2+ / Zn redox reaction; The rare earth metal ions of the rare earth metal salt are used as active materials in the positive electrode and react with Mn 2+ / MnO2 participate in the reaction together.

2. The electrolytic MnO2-Zn battery according to claim 1, wherein: The rare earth metal ions include at least one of europium, cerium, holmium and gadolinium.

3. The electrolytic MnO2-Zn battery according to claim 1 or 2, wherein: The electrolyte also includes a pH adjusting solution, which adjusts the pH of the electrolyte to 1.5-2.

5.

4. The electrolytic MnO2-Zn battery according to claim 3, wherein: The rare earth metal ions act as the supporting center of the MnO2 structure, shielding the Mn 2+ During the oxidation process of MnO2 3+ Production of intermediates.

5. The electrolytic MnO2-Zn battery according to claim 1 or 2, wherein: The rare earth metal salt includes at least one of europium acetate, holmium acetate, cerium acetate and gadolinium acetate.

6. The electrolytic MnO2-Zn battery according to claim 3, wherein: The concentration of the pH adjusting solution is 0.1-1 mol / L; The pH adjusting solution includes at least one of a sulfuric acid solution, a hydrochloric acid solution, and a nitric acid solution.

7. The electrolytic MnO2-Zn battery according to claim 1 or 2, wherein: The concentration of the manganese salt is 0.1-5 mol / L; The concentration of the zinc salt is 0.1-5 mol / L; The concentration of the rare earth metal salt is 0.01-1 mol / L.

8. The electrolytic MnO2-Zn battery according to claim 1 or 2, wherein: The rare earth metal ions in the rare earth metal salt have a valence of +3.

9. The electrolytic MnO2-Zn battery according to claim 1 or 2, wherein: The zinc salt includes at least one of zinc sulfate, zinc chloride, zinc nitrate, zinc bromide and zinc acetate; The manganese salt includes at least one of manganese sulfate, manganese chloride, manganese nitrate, manganese bromide and manganese acetate.

10. An electrolyte for use in an electrolytic MnO2-Zn battery according to any one of claims 1 to 9.

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