Electrolytic MnO2-Zn battery and electrolyte

Abstract

The application 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 comprises an acidic solution of zinc salt, manganese salt and rare earth metal salt; a positive electrode, which is used for carrying out a redox reaction with the electrolyte and Mn 2+ / MnO2; a negative electrode, which is used for carrying out a redox reaction with the electrolyte and Zn 2+ / Zn; and a rare earth metal ion of the rare earth metal salt, which participates in the reaction together with Mn 2+ / MnO2 as an active substance at the positive electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage technology, and in particular to an electrolytic MnO2-Zn battery and electrolyte. BACKGROUND

[0002] Manganese (Mn) -based materials are expected to become the electrode material for large-scale use of the next generation of energy storage devices due to the multiple variable valence of manganese, the high theoretical capacity, environmental friendliness, resource abundance and cost-effectiveness of the redox characteristics of manganese, and the like.

[0003] However, when MnO2 is used as the positive electrode to perform the electrode reaction, it is difficult to avoid the disproportionation reaction of manganese ions caused by the Jahn-Teller effect, that is, when the manganese ions are trivalent, they are in a high-spin state, the electron distribution on the d orbital is asymmetric, which causes the lattice structure around the manganese ions to be deformed, ultimately leading to the disproportionation reaction of the MnO2 electrode and the decomposition of the MnO2 electrode into different components. At the same time, the limited intrinsic conductivity of MnO2 hinders the complete reaction, resulting in low charge / discharge efficiency, difficulty in achieving large load and high-rate cycling, and rapid degradation of battery life, thereby hindering the development of manganese-based batteries. SUMMARY

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

[0005] According to an embodiment of one aspect of the present application, 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, configured to perform a redox reaction of Mn 2+ / MnO2 with the electrolyte; a negative electrode, configured to perform a redox reaction of Zn 2+ / Zn with the electrolyte; and a rare earth metal ion of the rare earth metal salt as an active material in the positive electrode to participate in the reaction with Mn 2+ / MnO2.

[0006] According to an embodiment of the present application, the rare earth metal ion includes at least one of europium, cerium, holmium and gadolinium.

[0007] According to an embodiment of the present application, the electrolyte further comprises 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 application, the rare earth metal ion acts as a support center of the MnO2 structure, and shields the generation of Mn 2+ intermediate in the oxidation process of Mn 3+ to MnO2.

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

[0010] According to an embodiment of the present application, the pH adjusting solution has a concentration of 0.1-1 mol / L; and the pH adjusting solution comprises 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 application, 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 application, the rare earth metal ion in the rare earth metal salt has a valence of +3.

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

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

[0015] According to an embodiment of the present application, the rare earth metal has a unique f orbital and more electron transition energy levels, and is easy to couple with similar energy levels of the metal Mn. The present application uses the f orbital electron of the rare earth metal ion to adjust the deposition and dissolution process of the Mn 2+ / MnO2, that is, to reduce the multi-step conversion of the positive electrode reaction through d-f double orbital hybrid coupling, to realize one-step conversion of double electron transfer, to promote the full positive electrode reaction, and to improve the electrochemical performance of the electrolytic MnO2-Zn battery. The electrolytic MnO2-Zn battery of the present application combines the rare earth metal ion adjusted MnO2 positive electrode with the zinc negative electrode, and the assembled electrolytic MnO2-Zn battery has excellent electrochemical performance, high battery capacity and rate performance, and high stability after multiple cycles.

[0016] The electrolytic MnO2-Zn battery adjusted by the rare earth metal ion helps to promote the development of high-energy and high-power density aqueous batteries, and to promote the practical application of the next generation of safe and low-cost grid-scale energy storage systems. BRIEF DESCRIPTION OF DRAWINGS

[0017] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application taken in conjunction with the accompanying drawings, in which:

[0018] Figure 1 A reaction mechanism diagram of the rare earth metal ion adjusted positive electrode MnO2 of the embodiment of the present application is shown.

[0019] Figure 2 d-orbital of Mn and f-orbital of Eu in the conversion process between Mn and Eu of Example 1 of the present application are shown in the density of states distribution diagram before and after charging; 2+ and Mn 4+ and f-orbital of Eu in the conversion process between Mn and Eu of Example 1 of the present application are shown in the density of states distribution diagram before and after charging;

[0020] Figure 3 crystal field analysis diagram of the electronic structure of d-orbital of Mn and f-orbital of Eu in the charging and discharging process of Example 1 of the present application is shown;

[0021] Figure 4 analysis spectrum diagram of MnO2@Eu cathode of Example 1 of the present application and MnO2 of Comparative Example 1 is shown;

[0022] Figure 5 performance diagram of the half-cell assembled by MnO2@Eu cathode of Example 1 of the present application and MnO2 of Comparative Example 1, respectively, is shown;

[0023] Figure 6 performance diagram of electrolytic MnO2@Eu-Zn battery 2 of Example 2 and MnO2-Zn battery 2' of Comparative Example 2 is shown;

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

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

[0026] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. It should be understood, however, that the description which follows is merely exemplary and is not intended to limit the scope of the application. In the following detailed description of the embodiments of the present application, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to one skilled in the art that the embodiments of the present application can be practiced without these specific details. In other instances, well-known structures and techniques have not been described in detail in order to avoid unnecessarily obscuring aspects of the present application.

[0027] The terms used herein are merely used to describe specific embodiments and are not intended to limit the present application. The term "include" used herein indicates the presence of a feature, step, operation, but does not exclude the presence or addition of one or more other features.

[0028] In the case of a statement of the type "at least one of A, B and C", generally this is to be interpreted to mean that "A or B or C or any combination of these". In the case of a statement of the type "at least one of A, B or C" generally this is to be interpreted to mean "A or B or C or any combination of these". In the case of a statement of the type "at least one of A, B and C etc.", generally this is to be interpreted to mean that "A or B or C or any combination of these", etc.

[0029] In the present invention, the term "Jahn-Teller effect" refers to the disproportionation of Mn 3+ due to the presence of Mn 3+ ions. Mn 4 has four electrons in its d-orbital (d 3+ configuration). In an octahedral coordination environment, these four electrons are distributed over the t2g and eg orbitals. According to crystal field theory, in an ideally symmetrical octahedral field, the t2g orbitals are triply degenerate, while the eg orbitals are doubly degenerate. Specifically, Mn 3+ will cause the oxygen atoms surrounding it to stretch outwards, forming a slightly distorted octahedral structure. This distortion allows the electrons to redistribute to a lower energy state. For Mn 3+ , the most commonly observed distortion is an elongation of the octahedron along the z-axis (known as the elongational distortion), as this distortion best alleviates the degeneracy. Applied in a cathode material for a battery, the Jahn-Teller effect of Mn 3+ may cause the material structure to be unstable, which in turn affects the electrochemical performance. For example, it can cause capacity fading, as the structural changes can make it difficult for zinc ions to intercalate and deintercalate, or directly cause a loss of active material due to dissolution at the cathode material, thereby reducing the cycle stability and efficiency of the electrolytic MnO2-Zn battery.

[0030] The Jahn-Teller effect and the disproportionation reaction of Mn 2+ ions often lead to irreversible structural transitions and Mn 3 / Mn +ion dissolution, ultimately degrades the cycling stability of electrolytic MnO2-Zn batteries. The Jahn-Teller effect is indeed a challenging issue in battery materials, especially for those containing Mn metal, such as lithium-ion batteries. During the battery cycling process, especially during the charge and discharge of the battery, the injection and extraction of ions easily lead to the Jahn-Teller distortion of the crystal structure of the Mn metal, ultimately resulting in poor cycling stability and capacity reduction of the battery.

[0031] Manganese dioxide (MnO2) can undergo solid-state transformation and cation (i.e., Li + , Zn 2+ , Na + , H + ) intercalation during electrochemical reactions. It utilizes the reversible valence transition between Mn 3+ and Mn 4+ to facilitate large charge transfer and achieve high electrochemical potential, making MnO2 a typical positive electrode material with high energy density in secondary batteries.

[0032] The related art of the present application proposes an electrochemical method based on MnO2 electrolytic chemistry, which realizes the two-electron transfer reaction between solid MnO2 and liquid Mn 2+ ions. This innovative method can achieve a high theoretical capacity of 616 mAh g -1 of MnO2 and an output voltage of about 1.23 V (versus SHE), thus showing great prospects for the design of high-performance manganese-based batteries suitable for large-scale energy storage applications. However, it is found during implementation that the Jahn-Teller effect of Mn 3+ during the electrochemical transformation of MnO2 leads to chemical disproportionation, and the limited intrinsic conductivity of MnO2 hinders the complete electrolytic reaction, resulting in low charging and discharging efficiency of the prepared MnO2 battery, making it difficult to achieve large load and high rate cycling, and rapid decay of battery life, making it difficult to promote in application.

[0033] In the process of developing the concept of the present application, it is found that during the oxidation of Mn 2+ to MnO2, a chemical disproportionation process occurs due to the presence of Mn 3+ intermediates. This chemical disproportionation of Mn 3+ intermediates produces a certain intrinsic difference between chemical manganese dioxide (c-MnO2) and in-situ electrodeposited electrochemical manganese dioxide (e-MnO2). Although e-MnO2 can be reversibly deposited and dissolved, c-MnO2 is difficult to reversibly dissolve, thus hindering the improvement of the capacity of the MnO2 positive electrode. In addition, the Jahn-Teller effect of Mn 3+ results in Mn 3+Chemical disproportionation of ions and Mn 3+ Physical residual of ions in electrolyte, part of Mn 3+ ions dissolve into electrolyte, and the rest of Mn 3+ ions are oxidized to MnO2 solid deposited in positive electrode or reduced to Mn 2+ ions return to electrolyte. The cycle stability of electrolytic MnO2-Zn battery is reduced.

[0034] To solve the above problems, the present application adds rare earth metal ions in electrolyte, which can more easily couple with similar energy level (d orbital) of metal Mn by unique f orbital and more electron transition energy level of rare earth metal ions, shield Mn 3+ from producing intermediate, reducing multi-step conversion of electrode reaction, realizing one-step conversion of double electron transfer, and promoting sufficient electrode reaction.

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

[0036] According to an embodiment of the present application, the present application provides f orbital electron by adding rare earth metal ions in electrolyte, further adjusts Mn 2+ / MnO2 deposition and dissolution electrochemical process in positive electrode, shields Mn 3+ ion production, reduces multi-step conversion of electrode reaction, realizes one-step conversion of double electron transfer, promotes sufficient electrode reaction, and further improves electrochemical performance of electrolytic MnO2-Zn battery.

[0037] The above will be described in detail as follows.

[0038] The present application participates in reaction of positive electrode by rare earth metal ions (RE) as active substance in positive electrode. During charging, the positive electrode is deposited into solid MnO2 from Mn 2+ ion which is easily soluble in water, and the negative electrode is reduced into solid metal Zn from Zn 2+ ion, and the active substances of positive and negative electrodes are both formed into solid substances. During discharging, the positive electrode is dissolved out of Mn 2+ ion from solid MnO2, and the negative electrode is dissolved out of Zn 2+ ion from solid metal Zn, and the dissolved Mn 2+and Zn 2+ The ions return to the electrolyte, and the positive and negative active materials are both in liquid phase.

[0039] It can be understood that the f orbit of the rare earth metal ion is not filled with electrons, has more active electrons and more electron transition energy levels, is easy to combine with the metal Mn (d orbit of Mn) having similar energy levels, can be selected as a suitable MnO2 orbital hybrid coupling and energy band structure regulator, and the presence of the rare earth metal ion can reduce the Mn 2+ ion to Mn 3+ ion conversion, promotes the Mn 2+ ion to Mn 4+ ion direct conversion. The redox reaction of the rare earth metal ion can be coupled with the Mn 2+ / MnO2 reaction, which helps to improve the theoretical capacity of the electrode reaction. In addition, the electrolyte regulated by the rare earth metal ion helps to stabilize the structure of the MnO2 and improve the conductivity of the battery structure, and effectively reduces or even shields the generation of Mn 3+ ion, thereby helping to reduce the disproportionation reaction of the Mn 3+ ion and the physical residue of the Mn 3+ ion in the electrolyte, so that the assembled MnO2@RE-Zn battery (which can be understood as the electrolytic MnO2-Zn battery of the application) exhibits high surface capacity load, high efficiency and long cycle life.

[0040] In the process of screening the metal ions added to the electrolyte, it is found that if transition metal ions are added to the electrolyte, it is difficult to form interaction between the transition metal ions and Mn because the transition metal ions do not have an unfilled f electron orbit. And when using an organic solvent as the electrolyte, safety problems may also occur. The addition of the rare earth metal ion first endogenously increases the theoretical capacity of the MnO2, and in addition, due to the transfer of an f electron of the rare earth metal ion, a new f orbital charge storage energy level is introduced, so that the theoretical capacity of the MnO2 has the energy injection of the rare earth metal ion, thereby improving the surface capacity load of the MnO2@RE-Zn battery.

[0041] It should be noted that the electrolytic MnO2-Zn battery of the application avoids the use of a separator, which can effectively avoid the high cost brought by the separator, save the manufacturing time of the battery, and the electrolyte used is a single solution system, which further simplifies the battery preparation process. The positive electrode and the negative electrode of the battery both use a current collector, 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, avoiding the complex electrode preparation process and saving the production cycle and production cost of the battery.

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

[0043] According to the embodiment of the present application, the rare earth metal ions in the rare earth metal salt are +3 valence.

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

[0045] During charging:

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

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

[0048] During 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, the oxidation-reduction reaction between RE 3+ and RE 4+ is coupled with the reaction of Mn 2 + / MnO2, which improves the theoretical capacity of the electrode reaction and is more conducive to reducing the generation of Mn 3+ ions, thereby reducing the disproportionation reaction of Mn 3+ ions and reducing the Jahn-Teller effect. The electrode reaction principle of the electrolytic MnO2-Zn battery of the present application is the double deposition / dissolution mechanism of the positive electrode MnO2 / Mn 2+ and the negative electrode Zn 2+ / Zn, which further avoids the diffusion, migration and phase transformation of Mn ions in the crystal structure of the electrode material.

[0052] According to embodiments of the present invention, the rare earth metal ions include at least one selected from europium (Eu), cerium (Ce), holmium (Ho), and gadolinium (Gd). During the experiments conducted related to the present invention, it was found that the aforementioned rare earth metal ions can participate in the Mn cathode. 2+ During the redox reaction of MnO2, electrons in the f orbitals of rare earth metal ions couple with the d orbitals of metallic Mn, thereby achieving MnO2 redox reactions. 2+ / Mn 4+ One-step conversion of two-electron reaction, shielding Mn 3+ The generation of ions promotes Mn 2+ The deposition and dissolution process of MnO2 enables electrolytic MnO2-Zn batteries to undergo highly reversible and long-term cycling at high areal capacity. It should be noted that the rare earth metal ions mentioned above in this invention are merely illustrative examples; the unique f-orbital electrons of other rare earth metal ions can also couple with the d-orbital electrons of metallic Mn, resulting in electrolytic MnO2-Zn batteries with higher theoretical capacity.

[0053] According to embodiments of the present invention, the electrolyte further includes a pH adjusting solution, which adjusts the pH of the electrolyte to 1.5-2.5, for example, 1.5, 2, or 2.5. It should be noted that during the relevant experiments of this invention, it was found that adding rare earth metal salts to the electrolyte to adjust the pH to acidic levels, for example, a pH above 3, can reduce Mn. 3+ However, it cannot completely shield Mn. 3+ The formation of ions still involves some Mn. 3+ The ions formed the Jahn-Teller effect. When the pH was adjusted to 1.5–2.5, the synergistic effect of pH regulation and rare earth metal ions could shield Mn. 3+ Promote Mn 2+ The deposition and dissolution process of MnO2 promotes the deposition and dissolution of Mn. 2+ and Mn 4+ The direct two-electron transfer reaction pathway between them enables electrolytic MnO2-Zn batteries to undergo highly reversible and long-term cycling at high areal capacity. This invention employs the synergistic regulation of f-electrons and pH of rare-earth metal ions to shield Mn... 3+ Ions to promote Mn 2+ The one-step conversion of MnO2 electrolysis chemistry provides an innovative approach for developing high-performance aqueous batteries for large-scale energy storage.

[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 following diagram illustrates the reaction mechanism of rare earth metal ions regulating the positive electrode MnO2 according to an embodiment of the present invention. Figure 1 As shown, rare earth metal ions act as supporting centers for the MnO2 structure, shielding Mn 2+ During the oxidation to MnO2 process, Mn 3+ The formation of intermediates. In the octahedral configuration of MnO6, O along the z-axis is defined as O. I In the xy plane, O is defined as O. II Type. In Mn 2+ &RE 3+ In the complex structure, the rare earth squares coordinated with tetraoxygen and the MnO6 octahedra form two congruent triangular structures (Mn-O). I -Ru-O II The structure is very stable and Mn-O I Bond length and Mn-O II The bond lengths are the same. This will result in Mn 2+ During ionic oxidation, it can simultaneously gain two electrons, thus achieving a direct two-electron transfer reaction to maintain its approximately octahedral configuration and oxidize to Mn. 4+ Rare earth atoms can also serve as supporting centers for the MnO2 crystal structure, making it more stable. In electrolyte systems regulated by rare earth metal ions (Eu, Ce, Ho, Gd), trivalent rare earth metal ions (RE... 3+ ) can be with Mn 2+ Ion coupling, and the formation of fan-shaped MnO6 octahedral structures based on the square REO4 as the supporting center. 2+ & RE 3+ Complex structure. This complex structure can anchor Mn 2+ The MnO6 ion has one O atom along the Z-axis and one O atom along the xy-plane. This will result in Mn 2+ When ions are oxidized, the MnO6 octahedron does not undergo significant distortion and retains an approximately octahedral configuration, thus making it easier to transform into Mn with an approximately octahedral configuration. 4+ions. The above transformation process results in that the positive electrode reaction directly transforms Mn 2+ ions into Mn 4+ ions, directly shields Mn 3+ ions in a specific range of pH 1.5-2.5, reduces the complex intermediate reaction process, and realizes one-step transformation of the two-electron transfer reaction. At the same time, the oxidation and reduction of the rare earth metal ion coupled with the Mn 3+ ion also provides additional electron transfer for the electrode reaction, thereby providing additional capacity for the battery. 4+

[0056] It can be understood that the transformation between Mn 2+ ions and Mn 4+ ions is actually carried out in the MnO6 octahedral configuration, which is required for the crystal structure formed in the crystallization process.

[0057] According to an embodiment of the present application, 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 low in price. At the same time, the above acetate belongs to a weak acid, and does not cause a large impact on the pH of the electrolyte, and is more conducive to realizing pH regulation of the electrolyte together with the pH adjusting solution.

[0058] According to an embodiment of the present application, the concentration of the manganese salt is 0.1-5 mol / L, for example, 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 the zinc salt is 0.1-5 mol / L, for example, 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; and the concentration of the rare earth metal salt is 0.01-1 mol / L, for example, can be 0.01 mol / 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, and is preferably 0.09 mol / L. Adjusting the concentrations of the above materials in the above ranges can promote the rare earth metal ion to fully participate in the transformation of Mn 2+ ​The f-orbital electrons of the rare earth metal ions interact with the d-orbital of the Mn ions during the conversion of / MnO2, further shielding the Mn 2+ The conversion of / MnO2 3+ ions, thereby avoiding the generation of 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, the zinc salt and the manganese salt have high solubility in the aqueous electrolyte, and are consistent with the acid radical of the pH adjusting liquid or the rare earth metal salt, without introducing other impurities, thereby avoiding unnecessary influence on the redox process.

[0060] According to an embodiment of another aspect of the present application, an electrolyte for the electrolytic MnO2-Zn battery is provided.

[0061] According to an embodiment of the present application, the zinc ions in the zinc salt in the electrolyte participate in the redox reaction of Zn 2+ / Zn; the manganese ions in the manganese salt participate in the redox reaction of Mn 2+ / MnO2under the optimization of the rare earth metal ions, the f-orbital electrons of the rare earth metal ions and the d-orbital electrons of the Mn form double coupling, and the Mn 2+ / Mn 4+ is converted in one step, and the Mn 3+ ions are generated, promoting the deposition and dissolution of MnO2 / Mn 2+ . The above electrolyte can improve the theoretical capacity of the electrolytic MnO2-Zn battery, improve the energy density of the battery, help maintain the structural integrity of the positive electrode material, reduce the dissolution loss of the positive electrode active material, and prolong the cycle life of the battery. In addition, the rare earth metal ions can form a conductive network, promote the transmission of electrons, reduce the interface resistance, and help improve the charge and discharge rate of the battery and improve the rate performance.

[0062] According to an embodiment of another aspect of the present application, a method for assembling an electrolytic MnO2-Zn battery is provided, which comprises mixing a zinc salt, a manganese salt, a rare earth metal salt, and a pH adjusting liquid to prepare an electrolyte; using carbon felt or carbon cloth as a positive electrode, and using zinc or zinc alloy as a negative electrode to assemble an electrolytic MnO2-Zn battery.

[0063] According to an embodiment of the present application, by introducing the rare earth metal ions into the electrolyte, the f-orbital electrons of the rare earth metal ions and the d-orbital electrons of the Mn ions form double coupling, and the Mn 2+ / Mn 4+two-electron reaction, avoiding the generation of Mn 3+ ion, reducing the generation of Jahn-Teller effect.

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

[0065] The present application is further illustrated by the following examples and related test experiments and their results. In the following detailed description, for the sake of explanation, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present application. It is apparent, however, that one or more embodiments can be practiced without such specific details. In other instances, well-known methods have not been elaborated in detail in order not to unnecessarily obscure the related details of the examples described.

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

[0067] Example 1:

[0068] The 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 1 M MnSO4, 0.1 M H2SO4, and 0.09 M Eu acetate mixed solution as the electrolyte. The 3D structure of carbon felt can provide effective electrolyte contact reaction channels for the deposition and stripping of MnO2, and the MnO2@Eu half-cell 1 is assembled.

[0070] Figure 2 The d-orbital of Mn and the f-orbital of Eu in the conversion process between Eu ion regulated Mn 2+ and Mn 4+ of Example 1 of the present application before and after charging are shown. As shown in Figure 2 , it is shown that there is a strong interaction between the d-orbital and the f-orbital. Mn 2+ & Eu 3+ and Mn 3+ & Eu 4+ complex configuration Mn-dz2 and Eu-fz(x 2 -y 2 The energy distribution region and location of each energy level peak in the Mn-dz orbit are consistent, indicating that Mn-dz 2 Energy levels and Eu-fz(x) 2 -y 2 The orbitals are hybridized. Furthermore, the Mn-dx orbitals are hybridized. 2 -y 2 and Eu-fz 3 The energy distribution region of the orbit and the positions of each energy level peak are also consistent, revealing that Mn-dx 2 -y 2 and Eu-fz 3 The orbitals are also hybridized. Two sets of df biorbitals (dx 2 -y 2 &fz 3 and dz 2 &fz(x 2 -y 2 The hybrid coupling of Mn-dx is beneficial to the Mn-dx reaction in the Mn ion electrode reaction. 2 -y 2 and Mn-dz 2 Simultaneous electron conversion of orbitals facilitates the direct two-electron transfer reaction of Mn ions, thus promoting Mn... 2+ and Mn 4+ Direct conversion between them.

[0071] Figure 3 The diagram shows a crystal field analysis of the electronic structure of the d orbitals of Mn and the f orbitals of Eu during the charging and discharging process of Embodiment 1 of the present invention. Figure 3 As shown, Mn 2+ d orbitals of ions and Eu 3+ The f orbitals of ions readily couple due to their similar energy levels. (Mn) 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+ During the ion process, Eu-fz 3 The orbital energy level loses an electron. However, due to the interaction between the orbital energy levels of the Eu-f electrons, the Eu-fz orbital energy level... 3 The orbital energy level position did not rise. Due to the interaction between the Eu-f electron orbital energy levels, Eu-fz(x)2 -y 2 ) orbital energy level is significantly increased. While Mn-dx 2 -y 2 orbital energy level is not increased due to the coupling with Eu-fz 3 orbital energy level is not increased due to the coupling with Eu-fz 2 orbital energy level is significantly increased due to the coupling with Eu-fz 2 -y 2 ) orbital energy level is significantly increased. In Mn 2+ ions are oxidized to Mn 4+ ions, the orbital energy level of Mn-dx 2 -y 2 orbital energy level and Mn-dz 2 orbital energy level each loses one electron, realizing a one-step conversion of double electron transfer. Similarly, during the reduction of Mn 4+ ions to Mn 2+ ions, the orbital energy level of Mn-dx 2 -y 2 does not change with the position of the orbital energy level of Eu-fz 2 -y 2 ) and the orbital energy level of Mn-dz 2 is decreased with the decrease of the orbital energy level of Eu-fz 2 -y 2 ).

[0072] Comparative Example 1:

[0073] The assembly process of the MnO2 half-cell 1’:

[0074] The assembly process of the present comparative example 1 is generally the same as that of example 1, except that no rare earth metal ions are added in the present comparative example 1, and the MnO2 half-cell 1’ is assembled.

[0075] Figure 4 The analysis spectra of the MnO2@Eu positive electrode of example 1 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 the MnO2, b is the photoluminescence spectrum of the MnO2@Eu positive electrode and the MnO2 under the 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 sample, wherein Mn foil, Mn2O3 and MnO2 are used as reference standards, and d is the linear fitting curve of the Mn valence state in the electrode active material deposited on the carbon felt. Figure 4XRD phase structure analysis in a in a reveals that the deposited Mn02cathode is a tetragonal a-Mn02phase with tunnel structure, JPCDS No. 44-141. The XRD peaks of the Mn02@Eu cathode show a shift towards lower angles, revealing a lattice expansion phenomenon. This phenomenon is caused by the local distance change after the introduction of Eu atoms inside the Mn02cathode. Figure 4 b in a shows that the Mn02cathode has no fluorescence peak in the wavelength range of 570-650 nm, while the Mn02@Eu cathode shows three different fluorescence peaks. The peak at 579.5 nm of the Mn02@Eu cathode corresponds to the Eu 3+ ions 5 D0- 7 F0electronic transition. The relatively broad peak with two split peaks between 590-600 nm is attributed to 5 D0- 7 F1magnetic dipole transition (MDT), which is an intrinsic parity-allowed transition, independent of the local site symmetry. While the peak centered at about 617 nm comes from 5 D0- 7 F2electric dipole transition (EDT), which is a sensitive transition affected by the local site symmetry of Eu 3+ ions. The higher intensity of the EDT fluorescence peak compared to the MDT peak indicates that a small amount of Eu 3+ ions occupy the center-symmetric sites inside the Mn02host lattice, which is consistent with the high-symmetry center-occupied of Eu atoms in the Mn02structure from the theoretical simulation.

[0076] As Figure 4 c in a Figure 4 d shows that the Mn K-edge curve of the deposited Mn02is close to that of the Mn203standard sample, indicating that the average valence state of Mn is close to trivalence. However, the Mn K-edge curve of the Mn02@Eu sample is closer to that of the Mn02standard sample, indicating that the average valence state of Mn in the deposited Mn02@Eu is closer to tetravalence. Linear fitting of the K-edge XAFS absorption spectrum of Mn reveals a significantly higher average Mn valence state in the deposited Mn02@Eu (4.98) compared to that in Mn02(3.33), indicating that Eu ions facilitate the promotion of Mn oxidation.

[0077] Electrochemical tests were performed on the assembled Mn02@Eu half-cell and Mn02half-cell, respectively. Figure 5The performance of MnO2@Eu cathode of Example 1 and MnO2 of Comparative Example 1 assembled into half-cells is shown in the figure, wherein a is a voltage-time curve of MnO2@Eu half-cell and MnO2 half-cell under constant current charging at 12 mA, b is a charge-discharge curve of MnO2@Eu half-cell and MnO2 half-cell at 1 C and 8 C rates, respectively, and c is a comparison of rate performance of MnO2@Eu half-cell and MnO2 half-cell. As shown in a of Figure 5 , the voltage of MnO2 electrode of Comparative Example 1 first slowly increases to 1.08 V during constant current charging, and then tends to be stable as the charging time is prolonged. This process is accompanied by disproportionation of Mn 3+ ions, resulting in incomplete deposition of MnO2 cathode. However, the voltage of MnO2@Eu cathode remains stable at about 1.1 V as the charging time is prolonged. The stable and high voltage of MnO2@Eu cathode than that of Mn 3+ ions, indicating that the regulation strategy of Eu ions can promote Mn 2+ ions to be directly deposited into MnO2, thereby effectively shielding the generation of Mn 3+ ions. Under constant current charging at 12 mA to an area capacity of 12 mAh / cm 2 , the voltage curve of MnO2 electrode of Comparative Example 1 shows a climbing trend, which reveals that the deposition process of MnO2 electrode undergoes a multi-process transition of Mn 2+ → Mn 3+ → Mn 4+ However, the voltage curve of MnO2@Eu cathode rapidly reaches about 1.1 V at the initial stage of charging, and then remains stable, which indicates that the deposition process of MnO2 electrode only undergoes a two-electron transfer process of Mn 2+ → Mn 4+ , thereby avoiding the single-electron transfer processes of Mn 2+ → Mn 3+ and Mn 3+ → Mn 4+ , thereby avoiding the Jahn-Teller effect.

[0078] As shown in b of Figure 5 , 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, MnO2@Eu half-cell shows a significantly higher discharge capacity of 11.43 mAh / cm 2 compared to about 10.62 mAh / cm 2Even at a high rate of 8 C, the MnO2@Eu half-cell 1 still maintains a high discharge plateau of 0.84 V and a coulombic efficiency of 82.2%, which is better than the lower coulombic efficiency of 71.4% and the lower discharge plateau of 0.73 V of the MnO2 half-cell 1'.

[0079] like Figure 5 As shown in Figure c, the coulombic efficiency and energy density of the MnO2@Eu half-cell 1 gradually decrease with increasing discharge rate. When the discharge rate is restored to 1C, the MnO2@Eu half-cell 1 can recover to approximately 95.49% of the initial coulombic efficiency and approximately 93.54 Wh / m³. 2 The energy density of the MnO2 half-cell is higher than that of the MnO2@Eu half-cell 1'. 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] Example 2:

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

[0082] A 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 Comparative Example 2 is largely the same as that of Example 2, except that rare earth metal ions were not added in Comparative Example 2 to form 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, where a is the charge-discharge curve of MnO2-Zn battery 2' at different rates, b is the charge-discharge curve of electrolytic MnO2@Eu-Zn battery 2 at different rates, c is a comparison graph of the discharge capacity and discharge 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, the discharge capacity and voltage plateau gradually decrease with increasing discharge current. Compared to the MnO2-Zn battery 2', the electrolytic MnO2@Eu-Zn battery 2 shows a 1.01 mAh / cm³ increase at 1 C rate. 2 The discharge capacity and strong discharge voltage of 0.01 V were improved, resulting in a discharge capacity of 1.1 mAh / cm³ at an 8 C rate. 2 And increase the discharge voltage to 0.32 V. For example... Figure 6 As shown in d, the MnO2-Zn battery 2' only maintained about 158 ​​Wh / m³ after 400 cycles. 2 The first type of battery, MnO2@Eu-Zn, has a limited capacity and stops working after 500 cycles, while the second type, an electrolytic MnO2@Eu-Zn battery, can perform long cycles and can still be used after 1000 cycles.

[0089] Example 3:

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

[0091] To further explore the practical applications of electrolytic MnO2@Eu-Zn and its potential in large-scale energy storage, electrodes and separators (approximately 70 cm²) will be used. 2 Alternating placement of elements resulted in the assembly of a 1.2 Ah high-capacity MnO2@Eu-Zn battery.

[0092] Comparative Example 3:

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

[0094] The assembly process of Comparative Example 3 is largely the same as that of Example 3. The difference is that no rare earth metal ions were added in Comparative Example 3, and an ampere-hour-level MnO2-Zn large battery 3' was assembled.

[0095] Figure 7 Performance graphs 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. Among them, a is a test graph of the ampere-hour-level electrolytic MnO2@Eu-Zn large battery 3 lighting an LED, b is a charge-discharge curve graph of the ampere-hour-level electrolytic MnO2@Eu-Zn large battery 3, and c is a cycle performance graph 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 Figure a, the charged MnO2@Eu-Zn large battery 3 can light a lamp in the form of "Mn-Zn" composed of 66 diodes connected in full parallel. 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 MnO2@Eu-Zn large battery 3 exhibited a discharge capacity of approximately 975 mAh and a discharge plateau of approximately 1.9 V at 1 C, approximately 850 mAh and a discharge plateau of approximately 1.78 V at 4 C, and approximately 620 mAh and a discharge plateau of approximately 1.60 V at 8 C. Figure 7 As shown in Figure c, this high-capacity MnO2@Eu-Zn large-scale battery 3 exhibits excellent cycle performance. It maintains a high energy density of approximately 92 Wh / kg at 1 C, almost twice the energy density of the largest capacity lead-acid battery (~50 Wh / kg), and even maintains an energy density as high as 80 Wh / kg at 8 C. The superior performance of this electrolytic MnO2@Eu-Zn large-scale battery 3 contributes to the development of high-energy, high-power-density aqueous batteries and facilitates the practical application of next-generation safe, low-cost grid-scale energy storage systems.

[0097] Example 4:

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

[0099] The assembly process of Example 4 is largely the same as that of Example 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' of Comparative Example 2, respectively.

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

[0102] like Figure 8 As shown in Figure a, compared to MnO2-Zn battery 2', the electrolytic MnO2@RE-Zn battery 4, when charged to 12 mAh / cm³, exhibits better performance. 2 The charging current response under the areal capacity is improved by approximately 10 mAcm. -2The charging time has been shortened by approximately 15 minutes. For example... Figure 8 As shown in b, the discharge curves of electrolytic MnO2@RE-Zn batteries 4, regulated by different rare earth metal ions (Ce, Ho, Gd), show a flat discharge plateau at around 1.95 V and a discharge efficiency of approximately 11.2 mAh / cm³. 2 The high discharge capacity of the MnO2-Zn battery 2' is evident in its discharge curve, which shows a discharge plateau at only 1.93 V and a discharge capacity of 12 mAh / cm³. 2 It only exhibits 10.15 mAh / cm² at its charging capacity. 2 Low discharge capacity. For example... Figure 8 As shown in c, the electrolytic MnO2@RE-Zn battery 4 optimized with rare earth metal ions (Ce, Ho, Gd) achieves a coulombic efficiency and energy density exceeding 90% and 175 Wh / m³ at a 1C discharge rate. 2 The rare-earth metal ion-optimized electrolytic MnO2@RE-Zn battery 4 assembled in Example 4 exhibits stable high energy density, high coulombic efficiency, and long cycle stability, highlighting the effectiveness of the rare-earth metal ion regulation strategy.

[0103] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are 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 within the protection scope of the present invention.

Claims

1. An electrolytic MnO 2-Zn battery, comprising: an electrolyte, comprising an acidic solution of zinc salt, manganese salt and rare earth metal salt, the pH of the acidic solution being 1.5-2.5; positive electrode, for redox reaction with said electrolyte 2+ Mn / MnO2 negative electrode for a redox reaction with said electrolyte 2+ Zn In this context, the rare earth metal ions of the rare earth metal salt act as active materials at the positive electrode, reacting with Mn. 2+ MnO2 and MnO2 jointly participate in the reaction, with the rare earth metal ions acting as supporting centers for the MnO2 structure, shielding Mn through df orbital hybridization coupling. 2+ During the oxidation to MnO2 process, Mn 3+ The intermediate is generated to enable a one-step conversion via two-electron transfer; the rare earth metal ion comprising at least one of europium, holmium and gadolinium. 2.The electrolytic MnO 2-Zn battery according to claim 1, wherein, the electrolyte further comprises a pH adjusting solution, the pH adjusting solution adjusting the pH of the electrolyte to 1.5-2.

5. 3.The electrolytic MnO 2-Zn battery according to claim 1 or 2, wherein, the rare earth metal salt comprises at least one of europium acetate, holmium acetate and gadolinium acetate.

4. The electrolytic Mn02-Zn cell according to claim 2, wherein, the concentration of the pH adjusting solution being 0.1-1 mol / L; the pH adjusting solution comprising at least one of sulfuric acid solution, hydrochloric acid solution and nitric acid solution. 5.The electrolytic MnO 2-Zn battery according to claim 1 or 2, wherein, the concentration of the manganese salt being 0.1-5 mol / L; the concentration of the zinc salt being 0.1-5 mol / L; the concentration of the rare earth metal salt being 0.01-1 mol / L. 6.The electrolytic MnO 2-Zn battery according to claim 1 or 2, wherein, the rare earth metal ion in the rare earth metal salt is +3 valence. 7.The electrolytic MnO 2-Zn battery according to claim 1 or 2, wherein, the zinc salt comprises at least one of zinc sulfate, zinc chloride, zinc nitrate, zinc bromide and zinc acetate; the manganese salt comprises at least one of manganese sulfate, manganese chloride, manganese nitrate, manganese bromide and manganese acetate. 8.An electrolyte for the electrolytic MnO 2-Zn battery according to any one of claims 1-7.

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