Electrolyte and preparation method thereof, battery and preparation method, equipment and device thereof

Abstract

The embodiment of the invention provides an electrolyte, a preparation method thereof, a battery, a preparation method of the battery, equipment and a device, which are used for solving the problem of poor cycle performance of a solid-state battery. The electrolyte comprises a first solid electrolyte layer, a transition layer and a second solid electrolyte layer, the transition layer is located between the first solid electrolyte layer and the second solid electrolyte layer, and the transition layer is formed by interpenetration of the first solid electrolyte layer and the second solid electrolyte layer. The first solid electrolyte layer comprises cross-linked vinylene carbonate and a first lithium salt; and the second solid electrolyte layer comprises a polycarbonate compound, an inorganic solid electrolyte and a second lithium salt. On one hand, the first solid electrolyte layer is not easily consumed due to side reaction with the positive electrode. And on the other hand, the first solid electrolyte layer and the second solid electrolyte layer can form an integrated composite solid electrolyte through the transition layer, so that the ion transmission rate of the composite solid electrolyte can be improved. And the cycle performance of the solid-state battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and in particular, to an electrolyte and its preparation method, a battery and its preparation method, equipment and devices. Background Art

[0002] With the rapid development of the field of electric vehicles, solid-state batteries have become a hot topic in the research field of lithium batteries. A solid-state battery is a battery that uses solid electrodes and a solid electrolyte. The solid electrolyte can improve the energy density of the battery and has high safety because it is not volatile and does not have a flammable organic matrix.

[0003] However, the interfacial stability between the solid electrolyte and the positive electrode in the solid electrode is poor. Under the charged state, the polymer in the solid electrolyte is prone to redox reactions with strong oxidizing high-valent transition metal ions (such as Ni 4+ , Co 3+ etc.) in the positive electrode, resulting in the consumption of the polymer. In addition, the polymer long chains in the solid electrolyte will also degrade under the catalytic action of the materials contained in the positive electrode (such as transition metal oxides), leading to further consumption of the polymer in the solid electrolyte. With the consumption of the polymer in the solid electrolyte, the contact degree between the solid electrolyte and the positive electrode gradually decreases, resulting in the collapse of the internal structure of the battery, triggering micro-short circuits or even short circuits. Furthermore, it leads to a rapid decay of the battery capacity. Summary of the Invention

[0004] Embodiments of the present application provide an electrolyte and its preparation method, a battery and its preparation method, equipment and devices. The embodiments of the present application can alleviate the consumption of the electrolyte, reduce the interfacial impedance of the electrolyte, and improve the ionic conductivity of the electrolyte. Furthermore, the composite solid electrolyte in the embodiments of the present application can enable a secondary battery to have both high energy density and good cycle performance when applied to a secondary battery subsequently, and can improve the efficiency of extracting lithium from seawater when applied to a lithium extraction device subsequently.

[0005] To achieve the above object, the embodiments of the present application adopt the following technical solutions:

[0006] In a first aspect, a composite solid electrolyte is provided, including a first solid electrolyte layer, a transition layer, and a second solid electrolyte layer. The transition layer is located between the first solid electrolyte layer and the second solid electrolyte layer, and the transition layer is formed by the mutual penetration of the first solid electrolyte layer and the second solid electrolyte layer. The first solid electrolyte layer includes cross-linked poly(vinyl carbonate) and a first lithium salt. The second solid electrolyte layer includes a polycarbonate compound, an inorganic solid electrolyte, and a second lithium salt.

[0007] On the one hand, the cross-linked poly(vinyl carbonate) in the first solid electrolyte layer has strong antioxidant and chemical stability, and is not easily consumed by side reactions with the positive electrode, which can effectively improve the interfacial stability between the first solid electrolyte layer and the positive electrode. The polycarbonate compound in the second solid electrolyte layer has strong anti-reduction property and is not easily consumed by side reactions with the negative electrode, which can effectively improve the interfacial stability between the second solid electrolyte layer and the negative electrode.

[0008] On the other hand, both the polycarbonate compound and the cross-linked poly(vinyl carbonate) contain carbonate groups and belong to the same type of matrix. The same type of matrix has good compatibility, which is conducive to the mutual penetration of the first solid electrolyte layer and the second solid electrolyte layer, making the interface between the first solid electrolyte layer and the second solid electrolyte layer disappear and merge into one, forming a transition layer with a stable structure. Thus, the first solid electrolyte and the second solid electrolyte layer can also form an integrated composite solid electrolyte through the transition layer. There is no obvious interface between the layers of the composite solid electrolyte, and the interfacial contact is good, so the interfacial impedance of the composite solid electrolyte can be significantly reduced, and the ion transport rate of the composite solid electrolyte can be improved. Furthermore, the composite solid electrolyte of the embodiments of the present application can also endow the secondary battery with high energy density and good cycle performance when applied to the secondary battery subsequently.

[0009] In addition, the composite solid electrolyte of the embodiments of the present application has good lithium ion transport ability and good Li + selective permeability, which is also conducive to improving the efficiency of lithium extraction from seawater when applied to a lithium extraction device subsequently.

[0010] In a possible implementation manner, the above-mentioned transition layer includes cross-linked poly(vinyl carbonate), a first lithium salt, a polycarbonate compound, an inorganic solid electrolyte, and a second lithium salt. When the transition layer has the above composition, it can have good compatibility with both the first solid electrolyte layer and the second solid electrolyte layer, thereby improving the structural stability of the composite solid electrolyte. Thus, during the charge and discharge cycle process, the composite solid electrolyte can maintain an integrated structure, so that it can maintain low impedance and good ion transport rate, and further improve the cycle performance of the secondary battery.

[0011] In a possible implementation, a separator is provided in the first solid electrolyte layer. The separator has a plurality of through-holes, and crosslinked poly(vinyl carbonate) and a first lithium salt are filled in the through-holes. The separator can provide a certain degree of support, which can improve the structural stability of the first solid electrolyte layer, and further improve the structural stability of the composite solid electrolyte. In addition, when the crosslinked poly(vinyl carbonate) and the first lithium salt are filled in the through-holes, a continuous ion transport channel can be formed inside the first solid electrolyte layer. The continuous ion transport channel can shorten the ion transport path inside the first solid electrolyte layer. Thus, the ion transport rate of the first solid electrolyte layer can be improved.

[0012] In a possible implementation, the ionic conductivity of the composite solid electrolyte is 1×10 -4 S·cm -1 to 2×10 -4 S·cm -1 . When the ionic conductivity of the composite solid electrolyte is within this range, the ion transport rate in the electrochemical reaction can be effectively improved, thereby improving the cycling performance of the secondary battery. In addition, when the ionic conductivity of the composite solid electrolyte is within the above range, the efficiency of lithium extraction from seawater can be improved when it is subsequently applied to a lithium extraction device.

[0013] In a possible implementation, the polycarbonate compound in the second solid electrolyte layer includes at least one of poly(propylene carbonate), poly(ethylene carbonate), and poly(trimethyl carbonate). The above types of polycarbonate compounds have good compatibility with crosslinked poly(vinyl carbonate) and are not easily chemically reacted with crosslinked poly(vinyl carbonate), which can further improve the ion transport rate of the composite solid electrolyte and improve the electrochemical stability inside the composite solid electrolyte. In addition, on the one hand, the above types of polycarbonate compounds are not easily electrochemically reacted with the negative electrode, which can improve the interfacial stability between the composite solid electrolyte and the negative electrode. On the other hand, the polycarbonate compound selected from the above types can undergo a microdecomposition reaction by itself to obtain a liquid decomposition product. The liquid decomposition product can participate in the formation of the solid electrolyte interphase (SEI) in the negative electrode, thereby improving the stability of the negative electrode SEI.

[0014] In a possible implementation, the separator includes a cellulose membrane. On the one hand, the cellulose membrane has relatively large pores and a suitable porosity, capable of accommodating a relatively large amount of cross-linked poly(vinyl carbonate) and the first lithium salt. Thus, it is beneficial to form a continuous ion transport channel inside the separator, shorten the ion transport path inside the first solid electrolyte layer, and improve the ion transport rate of the first solid electrolyte layer. On the other hand, the cellulose membrane has high thermal stability and chemical stability, which is beneficial to improving the structural stability of the first solid electrolyte layer. In addition, the cellulose membrane also has advantages such as environmental friendliness, renewability, and good biocompatibility, and has good environmental protection performance.

[0015] In a possible implementation, the inorganic solid electrolyte in the second solid electrolyte layer includes at least one of lithium germanium aluminum phosphate, lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium titanium oxide. Lithium germanium aluminum phosphate, lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium titanium oxide are fast ion conductors and have relatively high mechanical strength. Lithium germanium aluminum phosphate, lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium titanium oxide are dispersed in the second solid electrolyte layer. On the one hand, it is possible to form a fast ion transport channel and further improve the ion transport rate of the composite solid electrolyte. On the other hand, during the charging of the secondary battery, lithium dendrites may form on the negative electrode. If the lithium dendrites continue to grow, they may pierce through the composite solid electrolyte layer and contact the positive electrode, resulting in an internal short circuit of the secondary battery, causing thermal runaway or even combustion and explosion of the secondary battery. Lithium germanium aluminum phosphate, lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium titanium oxide can improve the mechanical strength of the second solid electrolyte layer, inhibit the growth of lithium dendrites on the negative electrode, and reduce the risk of lithium dendrites piercing through the composite solid electrolyte and contacting the positive electrode. In addition, lithium germanium aluminum phosphate, lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium titanium oxide have relatively high reaction inertness with polycarbonate compounds and are not easily involved in side reactions with polycarbonate compounds, which is beneficial to improving the stability of the second solid electrolyte layer.

[0016] In a possible implementation, the first lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalato)borate. The presence of lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalato)borate can improve the antioxidant property of the first solid electrolyte layer. Thereby, it is possible to reduce the side reactions between the components in the first solid electrolyte layer and the positive electrode, and further improve the interfacial stability between the composite solid electrolyte and the positive electrode.

[0017] In a possible implementation, the second lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate. The second lithium salt can participate in the formation of the negative electrode SEI, and different types of second lithium salts will form different types of SEIs. When lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate participate in the formation of the negative electrode SEI, they can increase the content of lithium fluoride (LiF) in the SEI. In this way, the SEI with a higher LiF content can have low impedance and good stability, which is beneficial to reducing the internal resistance of the secondary battery and improving the stability of the negative electrode environment. Thereby further improving the cycling performance of the secondary battery.

[0018] In a second aspect, an embodiment of the present application provides a method for preparing a composite solid electrolyte for preparing the above composite solid electrolyte, including:

[0019] Preparing a crosslinked poly(vinyl carbonate) precursor;

[0020] Preparing a second solid electrolyte layer, the second solid electrolyte layer including a polycarbonate compound, an inorganic solid electrolyte, and a second lithium salt;

[0021] Bringing the crosslinked poly(vinyl carbonate) precursor into contact with the second solid electrolyte layer to obtain a composite solid electrolyte precursor;

[0022] Heating the composite solid electrolyte precursor to form a first solid electrolyte layer and a transition layer to obtain a composite solid electrolyte; wherein, the transition layer is located between the first solid electrolyte layer and the second solid electrolyte layer, and the transition layer is formed by the mutual penetration of the first solid electrolyte layer and the second solid electrolyte layer; the first solid electrolyte layer includes crosslinked poly(vinyl carbonate) and a first lithium salt.

[0023] In the above preparation method, the crosslinked poly(vinyl carbonate) precursor can include vinyl carbonate and a crosslinking agent, and the crosslinked poly(vinyl carbonate) precursor and the second solid electrolyte layer can mutually penetrate to form a precursor transition layer.

[0024] On the one hand, both the transition layer and the first solid electrolyte layer are obtained by in-situ polymerization of vinyl carbonate and a crosslinking agent in the crosslinked poly(vinyl carbonate) precursor, and the transition layer and the first solid electrolyte layer can form an integrated layer structure without an obvious interface.

[0025] On the other hand, the precursor transition layer is formed by the interpenetration of the cross-linked poly(vinyl carbonate) precursor and the second solid electrolyte layer. The precursor transition layer and the second solid electrolyte layer are continuously distributed. Thus, the formed transition layer is also continuously distributed with the second solid electrolyte layer, forming an integrated layer structure without an obvious interface. Therefore, the first solid electrolyte layer and the second solid electrolyte layer can form an integrated composite solid electrolyte through the transition layer. In the composite solid electrolyte, there is no obvious interface between the first solid electrolyte layer, the transition layer, and the second solid electrolyte layer, thereby significantly reducing the interfacial impedance of the composite solid electrolyte. In addition, in the composite solid electrolyte, the contact between the layer structures is uniform, and almost no voids are generated, which can effectively improve the ion transport rate between the layer structures, and further improve the ion transport rate of the composite solid electrolyte.

[0026] In a possible implementation manner, the preparation of the cross-linked poly(vinyl carbonate) precursor specifically includes:

[0027] Mix the first lithium salt, vinyl carbonate, cross-linking agent, and initiator evenly to obtain a precursor slurry;

[0028] Load the precursor slurry onto the separator to obtain a cross-linked poly(vinyl carbonate) precursor, wherein the separator has a plurality of through holes, and the precursor slurry is filled in the through holes.

[0029] The separator can be used to accommodate the precursor slurry and inhibit the flow of the precursor slurry. Thus, after the cross-linked poly(vinyl carbonate) precursor contacts the second solid electrolyte layer, the precursor slurry can penetrate to the surface layer of the second solid electrolyte layer without flowing to other positions, which is beneficial to the smooth progress of the in-situ polymerization reaction.

[0030] In a possible implementation manner, the mass ratio of vinyl carbonate to the cross-linking agent is 4:1 to 6:1; the mass ratio of vinyl carbonate to the first lithium salt is 9:1 to 10:1. Controlling the mass ratio of vinyl carbonate to the cross-linking agent within the above suitable range can, on the one hand, form poly(vinyl carbonate) with a suitable degree of cross-linking, so that the first solid electrolyte layer has both high mechanical strength and good flexibility. On the other hand, it can make the poly(vinyl carbonate) contain more vinyl carbonate-derived structural units, and the vinyl carbonate-derived structural units can improve the ion transport rate of the cross-linked poly(vinyl carbonate), thereby improving the ionic conductivity of the composite solid electrolyte.

[0031] In a possible implementation manner, the volume ratio of the precursor slurry to the area of the separator is 8 μL·cm -2 to 12 μL·cm -2By controlling the ratio of the volume of the precursor slurry to the area of the separator within the above-mentioned appropriate range, an appropriate amount of the precursor slurry can be loaded on the separator, thereby forming a first solid electrolyte layer and a transition layer with appropriate thicknesses. The first solid electrolyte layer having an appropriate thickness can enable the first solid electrolyte layer to have a lower bulk impedance, thereby reducing the impedance of the composite solid electrolyte. The transition layer having an appropriate thickness can enhance the stability of the internal structure of the composite solid electrolyte, which is beneficial for the composite solid electrolyte to maintain a lower impedance and a higher ionic conductivity.

[0032] In a possible implementation, the mass ratio of the polycarbonate compound to the inorganic solid electrolyte is from 1:2 to 3:7; the mass ratio of the polycarbonate compound to the second lithium salt is from 4:1 to 6:1.

[0033] On the one hand, controlling the mass ratio of the polycarbonate compound to the inorganic solid electrolyte within the above-mentioned range is beneficial for the uniform dispersion of the inorganic solid electrolyte in the polycarbonate compound matrix. Thus, not only can the inorganic solid electrolyte be connected through the polycarbonate compound matrix to form a continuous ion transport channel, but also the crystallinity of the polycarbonate compound matrix can be reduced, thereby enhancing the ion transport rate of the polycarbonate compound matrix. In addition, an appropriate content of the polycarbonate compound in the second solid electrolyte layer is also beneficial for enhancing the flexibility of the second solid electrolyte layer.

[0034] On the other hand, controlling the mass ratio of the polycarbonate compound to the second lithium salt within the above-mentioned range can enable the second solid electrolyte layer to have good flexibility while containing a relatively large amount of the second lithium salt, thereby enhancing the ion transport rate of the second solid electrolyte layer and further enhancing the ionic conductivity of the composite solid electrolyte.

[0035] In a possible implementation, the preparation of the second solid electrolyte layer specifically includes:

[0036] Dissolving the polycarbonate compound, the inorganic solid electrolyte, and the second lithium salt in an organic solvent to obtain a second solid electrolyte layer slurry;

[0037] Placing the second solid electrolyte layer slurry in a mold and removing the organic solvent to obtain the second solid electrolyte layer.

[0038] By preparing the second solid electrolyte layer through the above steps, the size of the second solid electrolyte layer can be flexibly adjusted, and the preparation efficiency of the composite solid electrolyte can be enhanced.

[0039] In a possible implementation, the thickness of the above-mentioned second solid electrolyte layer slurry is from 200 μm to 300 μm. Controlling the thickness of the second solid electrolyte layer slurry within this range is beneficial for forming a second solid electrolyte layer with an appropriate thickness.

[0040] In a possible implementation, the thickness of the prepared second solid electrolyte layer is 80 μm to 120 μm. Controlling the thickness of the second solid electrolyte layer within a suitable range can endow the second solid electrolyte layer with appropriate permeability. Furthermore, when the crosslinked poly(vinyl carbonate) precursor contacts the second solid electrolyte layer subsequently, the crosslinked poly(vinyl carbonate) precursor and the second solid electrolyte layer can penetrate each other to form a precursor transition layer with a suitable thickness. Thus, the second solid electrolyte layer and the transition layer in the composite solid electrolyte can have appropriate thicknesses. The second solid electrolyte layer in the composite solid electrolyte having an appropriate thickness can inhibit the formation of lithium dendrites. The transition layer having an appropriate thickness can enhance the stability of the internal structure of the composite solid electrolyte, which is conducive to the composite solid electrolyte maintaining a low impedance and a high ionic conductivity.

[0041] In a third aspect, an embodiment of the present application provides a secondary battery, including a positive electrode, a negative electrode, and any one of the above composite solid electrolytes. The composite solid electrolyte is filled between the positive electrode and the negative electrode. The first solid electrolyte layer of the composite solid electrolyte contacts the positive electrode, and the second solid electrolyte layer of the composite solid electrolyte contacts the negative electrode.

[0042] In a possible implementation, the positive electrode includes a nickel-cobalt-manganese ternary positive electrode material, and the negative electrode includes metallic lithium or a lithium alloy. Both the above positive electrode and negative electrode have a high specific capacity. Combined with any one of the above composite solid electrolytes, they can have a high capacity utilization, thereby improving the specific energy of the secondary battery. Furthermore, the energy density of the secondary battery is improved.

[0043] In a fourth aspect, an embodiment of the present application provides a method for manufacturing a secondary battery for manufacturing the above secondary battery, including:

[0044] Preparing a crosslinked poly(vinyl carbonate) precursor;

[0045] Preparing a second solid electrolyte layer, where the second solid electrolyte layer includes a polycarbonate compound, an inorganic solid electrolyte, and a second lithium salt;

[0046] Stacking the positive electrode, the crosslinked poly(vinyl carbonate) precursor, the second solid electrolyte layer, and the negative electrode in sequence to obtain an electrode assembly;

[0047] Heating the electrode assembly to form a first solid electrolyte layer and a transition layer, thereby obtaining a secondary battery; wherein the transition layer is located between the first solid electrolyte layer and the second solid electrolyte layer, and the transition layer is formed by the mutual penetration of the first solid electrolyte layer and the second solid electrolyte layer; the first solid electrolyte layer includes crosslinked poly(vinyl carbonate) and a first lithium salt.

[0048] In the above preparation method, the cross-linked poly(vinyl carbonate) precursor may include vinyl carbonate and a cross-linking agent. After the positive electrode, the cross-linked poly(vinyl carbonate) precursor, the second solid electrolyte layer, and the negative electrode are stacked in sequence, the vinyl carbonate and the cross-linking agent in the cross-linked poly(vinyl carbonate) precursor can not only penetrate to the surface layer of the second solid electrolyte layer, but also penetrate into the gap between the cross-linked poly(vinyl carbonate) precursor and the positive electrode to make full contact with the positive electrode. During the heating process, an in-situ polymerization reaction occurs between the vinyl carbonate and the cross-linking agent. Similar to the formation process of the transition layer and the first solid electrolyte layer, the positive electrode and the first solid electrolyte layer can also form a layer structure with close contact and almost no voids through an in-situ polymerization reaction. Thereby, the interfacial contact between the composite solid electrolyte and the positive electrode can be improved, the interfacial impedance between the composite solid electrolyte and the positive electrode can be reduced, and the interfacial ion transport rate between the composite solid electrolyte and the positive electrode can be increased.

[0049] In a fifth aspect, an embodiment of the present application provides a battery system, which includes a battery module, and the battery module includes a plurality of the secondary batteries of any one of the above.

[0050] In a sixth aspect, an embodiment of the present application provides an electronic device, which includes a housing, and electronic components and a battery accommodated in the housing. The battery powers the electronic components, and the battery includes the secondary battery of any one of the above.

[0051] In a seventh aspect, an embodiment of the present application provides a lithium extraction device, which includes a positive electrode, a negative electrode, and the composite solid electrolyte of any one of the above. The composite solid electrolyte is used to separate the positive electrode and the negative electrode, and the composite solid electrolyte does not contact the positive electrode and the negative electrode. Description of the Drawings

[0052] Figure 1 It is a schematic structural diagram of a solid electrolyte provided by an embodiment of the present application;

[0053] Figure 2 It is a schematic structural diagram of a secondary battery provided by an embodiment of the present application;

[0054] Figure 3 It is a schematic structural diagram of a composite solid electrolyte provided by an embodiment of the present application;

[0055] Figure 4 It is a schematic structural diagram of another composite solid electrolyte provided by an embodiment of the present application;

[0056] Figure 5 It is a schematic structural diagram of a seawater lithium extraction device provided by an embodiment of the present application;

[0057] Figure 6SEM image of the surface of the first solid electrolyte layer in the secondary battery prepared in Example 1 of the present application;

[0058] Figure 7 SEM image of the surface of the second solid electrolyte layer in the secondary battery prepared in Example 1 of the present application;

[0059] Figure 8 XRD pattern of the composite solid electrolyte in the secondary battery prepared in Example 1 of the present application;

[0060] Figure 9 Schematic diagram for comparing the discharge capacity - cycle number graphs of the secondary batteries prepared in Example 1 and Comparative Examples 1 - 2 of the present application;

[0061] Figure 10 Schematic diagram for comparing the Coulomb efficiency - cycle number graphs of the secondary batteries prepared in Example 1 and Comparative Examples 1 - 2 of the present application;

[0062] Figure 11 Schematic diagram for comparing the Coulomb efficiency - cycle number graphs of the secondary batteries prepared in Example 2 and Comparative Example 3 of the present application;

[0063] Figure 12 Schematic diagram for comparing the electrochemical impedance spectroscopy (EIS) test results of the stainless steel (SS) / lithium (Li) batteries prepared in Example 1 and Comparative Example 4 of the present application;

[0064] Figure 13 Schematic diagram of the structure of a battery system provided by an embodiment of the present application. Detailed implementation manners

[0065] Next, the technical solutions in the embodiments of the present application will be described with reference to the accompanying drawings in the embodiments of the present application. Among them, in the description of the present application, unless otherwise specified, " / " indicates that the objects associated before and after are in an "or" relationship. For example, A / B can represent A or B; "and / or" in the present application is only a description of the association relationship of the associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Here, A and B can be singular or plural.

[0066] Moreover, in the description of the present application, unless otherwise specified, "a plurality of" means two or more than two. "At least one of the following" or its similar expressions refer to any combination of these items, including any combination of single item or plural items. For example, at least one of a, b, or c can represent: a, b, c, a - b, a - c, b - c, or a - b - c, where a, b, and c can be single or plural.

[0067] Meanwhile, in the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of the present application should not be construed as more preferred or more advantageous than other embodiments or design solutions. Rather, the use of words such as "exemplary" or "for example" is intended to present relevant concepts in a specific manner for easy understanding.

[0068] In the embodiments of the present application, the 3C battery can represent a capacity-type lithium secondary battery made of material systems such as lithium nickel cobalt manganese oxide and lithium manganese oxide, represented by 3C products. The so-called "3C products" are the collective term for three types of electronic products: computer, communication, and consumer electronics, also known as "information appliances".

[0069] In the embodiments of the present application, the power battery can represent a secondary battery that provides a power source for tools, for example, a secondary battery that provides a power source for electric vehicles, electric trains, electric bicycles, and golf carts.

[0070] As mentioned in the background art, with the consumption of the polymer in the solid electrolyte, it will cause the collapse of the internal structure of the battery, triggering micro-shorts or even short circuits, thereby resulting in a rapid decline in the battery capacity. Thus, it is still difficult for solid-state batteries to balance high energy density and good cycle performance.

[0071] To solve the above problems, some related technologies disclose a solid electrolyte. As an example, Figure 1 shows a secondary battery applying the solid electrolyte. As Figure 1As shown, the solid electrolyte 10 is located between the lithium negative electrode 20 and the positive electrode 30, and the positive electrode 30 includes a nickel-cobalt-manganese (NCM) ternary cathode material. Among them, the solid electrolyte 10 includes a polyethylene oxide-succinonitrile (PEO-SN) electrolyte layer 11 disposed facing the lithium negative electrode 20 and a polyacrylonitrile-lithium titanium aluminum phosphate (PAN-LATP) electrolyte layer 12 disposed facing the positive electrode 30. However, this solid electrolyte is prepared by a solution casting method, that is, the PAN-LATP electrolyte layer and the PEO-SN electrolyte layer are separately prepared by the solution casting method, and then the two are combined together by the viscosity of the polymers on the surfaces of the PAN-LATP electrolyte layer and the PEO-SN electrolyte layer, thereby constructing the solid electrolyte. It can be understood that there is an obvious interface between the PAN-LATP electrolyte layer and the PEO-SN electrolyte layer, which will significantly increase the interfacial impedance. In addition, the PAN-LATP electrolyte layer and the PEO-SN electrolyte layer are combined by the viscosity of the polymers on the surfaces of the electrolyte layers, and there is only a physical contact on the surface between the two, which may cause voids, uneven contact, etc., resulting in a decrease in the ion transport rate at the interface.

[0072] To solve the above technical problems, the embodiments of the present application provide a composite solid electrolyte applied to secondary batteries, a preparation method thereof, a battery and a preparation method thereof, an electronic device, and a lithium extraction device. The composite solid electrolyte includes a first solid electrolyte layer, a transition layer, and a second solid electrolyte layer. The transition layer is located between the first solid electrolyte and the second solid electrolyte layer, and the transition layer is formed by the mutual penetration of the first solid electrolyte layer and the second solid electrolyte layer. Among them, the first solid electrolyte layer includes crosslinked poly(vinyl carbonate) and a first lithium salt. The second solid electrolyte layer includes a polycarbonate compound (Polycarbonate, PC), an inorganic solid electrolyte, and a second lithium salt.

[0073] On the one hand, the crosslinked poly(vinyl carbonate) in the first solid electrolyte layer has strong antioxidant and chemical stability, is not easily consumed by side reactions with the positive electrode, and can effectively improve the interfacial stability between the first solid electrolyte layer and the positive electrode. The polycarbonate compound in the second solid electrolyte layer has strong anti-reduction property, is not easily consumed by side reactions with the negative electrode, and can effectively improve the interfacial stability between the second solid electrolyte layer and the negative electrode.

[0074] On the other hand, both the polycarbonate compound and the cross-linked polyvinyl carbonate contain carbonate groups and belong to the same type of matrix. Matrices of the same type have good compatibility, which is conducive to the mutual penetration of the first solid electrolyte layer and the second solid electrolyte layer, causing the interface between the first solid electrolyte layer and the second solid electrolyte layer to disappear and merge into one, forming a transition layer with a stable structure. Thus, the first solid electrolyte and the second solid electrolyte layer can also form an integrated composite solid electrolyte through the transition layer. There is no obvious interface between the layers of the composite solid electrolyte, and the interface contact is good, so the interfacial impedance of the composite solid electrolyte can be significantly reduced, and the ion transport rate of the composite solid electrolyte can be improved. Furthermore, the composite solid electrolyte of the embodiment of the present application can also endow the secondary battery with high energy density and good cycling performance when applied to a secondary battery subsequently.

[0075] In addition, the composite solid electrolyte of the embodiment of the present application has good lithium ion transport ability and good Li + selective permeability, which is also conducive to improving the efficiency of lithium extraction from seawater when applied to a lithium extraction device subsequently.

[0076] Figure 2 It is a schematic structural diagram of the secondary battery provided by the embodiment of the present application. As Figure 2 shown, the secondary battery includes a positive electrode 100, a negative electrode 200, a composite solid electrolyte 300, a positive electrode tab 400, a negative electrode tab 500, and a housing 600. Among them, the composite solid electrolyte 300 is disposed between the positive electrode 100 and the negative electrode 200 and is in contact with the positive electrode 100 and the negative electrode 200. The positive electrode 100, the composite solid electrolyte 300, and the negative electrode 200 are arranged in sequence, and the layers arranged in sequence are wound or folded to form an electrode assembly and assembled into the housing 600. A sealing area 610 is provided at the top of the housing 600, and the sealing area 610 is used for the encapsulation of the secondary battery. The positive electrode tab 400 is connected to the positive electrode 100, and the negative electrode tab 500 is connected to the negative electrode 200. The positive electrode tab 400 and the negative electrode tab 500 are used to conduct current out of the electrode assembly for charging and discharging. During charging, active lithium ions are removed from the positive electrode active material (not shown in the figure) of the positive electrode 100, pass through the composite solid electrolyte 300, and then are embedded in the negative electrode active material (not shown in the figure) of the negative electrode 200, or deposited on the surface of the negative electrode 200 to form lithium metal. During discharging, active lithium ions are removed from the negative electrode active material, or lithium metal is stripped to form active lithium ions, and then inserted into the positive electrode active material after passing through the composite solid electrolyte 300. The composite solid electrolyte 300 can isolate the positive electrode 100 and the negative electrode 200 while transferring active lithium ions, avoiding the direct contact between the positive electrode 100 and the negative electrode 200 and reducing the risk of short circuit.

[0077] The secondary battery according to the embodiment of the present application may include, but is not limited to, at least one of a lithium-ion battery and a lithium metal battery, and the embodiment of the present application does not specifically limit this.

[0078] In the secondary battery provided by the embodiment of the present application, the positive electrode may include a positive electrode current collector and a positive electrode material layer coated on the surface of the positive electrode current collector. In addition to the positive electrode active material, the positive electrode material layer may further include a certain amount of binder, conductive agent and other components. Among them, the positive electrode current collector may be a metal foil, such as aluminum foil, gold foil, platinum foil, etc. The positive electrode active material can reversibly intercalate / deintercalate active lithium ions. The positive electrode active material includes, but is not limited to, at least one of lithium cobaltate, ternary materials (nickel-cobalt-manganese system), lithium manganate, lithium nickelate and lithium iron phosphate.

[0079] Among them, the ternary material may be, for example, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 (NCM111), LiNi 0.5 Mn 0.2 Co 0.3 O2 (NCM523), LiNi 0.6 Mn 0.2 Co 0.2 O2 (NCM622), LiNi 0.8 Mn 0.1 Co 0.1 O2 (NCM811), LiNi 0.9 Mn 0.05 Co 0.05 O2 (NCM9055), etc. The binder may be, for example, polyvinylidene fluoride (poly 1,1-difluoroethylene, PVDF), and the conductive agent may be, for example, conductive carbon black (Super P), graphite, amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc. The positive electrode current collector, positive electrode active material, binder and conductive agent used for preparing the positive electrode are only exemplary descriptions, and the embodiment of the present application does not limit this. Taking the positive electrode active material as an example, theoretically, it can be a compound that can reversibly intercalate and deintercalate active lithium ions.

[0080] In some embodiments of the present application, the secondary battery may be a lithium metal battery. The positive electrode of the lithium metal battery may be the above-mentioned positive electrode. The negative electrode of the lithium metal battery may be a lithium negative electrode, and the lithium negative electrode may include lithium metal or a lithium alloy. Among them, the lithium alloy may be, for example, at least one of a lithium-silicon alloy, a lithium-aluminum alloy, a lithium-tin alloy, and a lithium-indium alloy. During charging, the active lithium ions released from the positive electrode active material may be deposited on the surface of the lithium negative electrode to form lithium metal after passing through the composite solid electrolyte. During discharging, the lithium metal may be stripped to form active lithium ions, and the active lithium ions may be inserted into the positive electrode active material after passing through the composite solid electrolyte. The lithium negative electrode has a high specific capacity. Taking the lithium negative electrode including lithium metal as an example, its specific capacity can reach 3860 mAh·g -1 , thereby allowing the secondary battery to have a high energy density.

[0081] In a possible implementation, the secondary battery may be a lithium metal battery. In the positive electrode of the secondary battery, the positive electrode active material may be a ternary material. The lithium negative electrode may include lithium metal or a lithium alloy. The ternary material has a high specific capacity and can match the capacity of the lithium negative electrode, improving the specific energy of the secondary battery and thus the energy density of the secondary battery. Furthermore, the secondary battery has both a high energy density and good cycle performance and can be applied to 3C batteries or power batteries, improving the electrical performance and reliable durability of 3C batteries or power batteries.

[0082] The secondary battery provided by the embodiments of the present application may also be a lithium-ion battery. The positive electrode of the lithium-ion battery may be the above-mentioned positive electrode. The negative electrode of the lithium-ion battery may include a negative electrode current collector and a negative electrode material layer coated on the surface of the negative electrode current collector. In addition to the negative electrode active material, the negative electrode material layer may also include a certain amount of binder, conductive agent, and other components. Among them, the negative electrode current collector may be a metal foil, such as copper foil, gold foil, platinum foil, etc. The negative electrode active material is at least one of a carbon material, an alloying material, and a silicon material capable of inserting and extracting active lithium ions. The carbon-based materials include, but are not limited to, one or more of graphite, hard carbon, soft carbon, and graphene. The alloying materials include, but are not limited to, one or more of tin, tin-carbon, tin-oxygen, and tin metal compounds. The silicon materials include, but are not limited to, one or more of silicon, silicon-carbon, and silicon-oxygen. The binder may be, for example, sodium carboxymethyl cellulose (CMC-Na) and / or styrene-butadiene rubber (SBR), etc. The conductive agent may be, for example, acetylene black, graphite, amorphous carbon, etc. The above-mentioned negative electrode current collector, negative electrode active material, binder, and conductive agent used for preparing the negative electrode are only illustrative, and the embodiments of the present application are not limited thereto. Taking the negative electrode active material as an example, theoretically, it may be a substance capable of reversibly inserting and extracting active lithium ions.

[0083] Figure 3 It is a schematic structural diagram of the composite solid electrolyte provided by the embodiments of the present application. As Figure 3As shown, the composite solid electrolyte 300 may include a first solid electrolyte layer 310, a transition layer 320, and a second solid electrolyte layer 330. The transition layer 320 is located between the first solid electrolyte layer 310 and the second solid electrolyte layer 330, and the transition layer 320 is formed by the mutual penetration of the first solid electrolyte layer 310 and the second solid electrolyte layer 330.

[0084] It can be understood that the above-mentioned "mutual penetration of the first solid electrolyte layer 310 and the second solid electrolyte layer 330" may indicate a material exchange between the first solid electrolyte layer 310 and the second solid electrolyte layer 330. Different from the surface contact between the two electrolyte layers in the related art, after the material exchange, the interface between the first solid electrolyte layer 310 and the second solid electrolyte layer 330 disappears and merges into one body to form the transition layer 320. Thus, the first solid electrolyte layer 310 and the second solid electrolyte layer 330 can form an integrated composite solid electrolyte 300 through the transition layer 320. There is no obvious interface between the first solid electrolyte layer 310, the transition layer 320, and the second solid electrolyte layer 330 in the composite solid electrolyte 300, thereby significantly reducing the interfacial impedance inside the composite solid electrolyte 300. In addition, the layer structures in the composite solid electrolyte 300 can be in uniform contact with almost no voids generated, which can effectively improve the ion transport rate between the layer structures, and further improve the ion transport rate of the composite solid electrolyte 300.

[0085] In some embodiments of the present application, the first solid electrolyte layer 310 is used to contact the positive electrode of the secondary battery, and the first solid electrolyte layer 310 includes cross-linked poly(vinyl carbonate) and a first lithium salt. Cross-linked poly(vinyl carbonate) has strong antioxidant properties and is not easily oxidized by the strongly oxidizing high-valent transition metal ions in the positive electrode, and has good electrochemical stability. In addition, cross-linked poly(vinyl carbonate) has a three-dimensional network structure. Compared with linear polymer polymers, cross-linked poly(vinyl carbonate) has higher chemical stability and is not easily catalyzed by the materials contained in the positive electrode to degrade. Therefore, the probability of side reactions and consumption between cross-linked poly(vinyl carbonate) and the positive electrode is significantly reduced, thereby effectively improving the interfacial stability between the first solid electrolyte layer 310 and the positive electrode. This can improve the stability of the internal structure of the battery during the charge and discharge cycle, and further delay the capacity decay of the secondary battery.

[0086] In some embodiments of the present application, the second solid electrolyte layer 330 is used to contact the negative electrode of the secondary battery, and the second solid electrolyte layer 330 includes a polycarbonate compound, an inorganic solid electrolyte, and a second lithium salt. The polycarbonate compound can be represented as a linear polymer polymer containing a carbonate group in the molecular chain. Both the polycarbonate compound and cross-linked poly(vinyl carbonate) contain carbonate groups and belong to the same type of matrix.

[0087] On the one hand, polycarbonate compounds and cross-linked poly(vinyl carbonate) contain similar functional groups and are not prone to chemical reactions, which can enhance the electrochemical stability inside the composite solid electrolyte 300. On the other hand, the same type of matrix has good compatibility, which is conducive to the mutual penetration of the first solid electrolyte layer 310 and the second solid electrolyte layer 330 to form a structurally stable transition layer 320, thereby enhancing the ion transport rate of the composite solid electrolyte. In addition, polycarbonate compounds also have strong anti-reduction properties and are not easily involved in redox reactions with the negative electrode, which can effectively improve the interfacial stability between the second solid electrolyte layer 330 and the negative electrode.

[0088] Therefore, the composite solid electrolyte 300 provided by the embodiments of the present application not only has good interfacial stability and a wide electrochemical window with both the positive electrode and the negative electrode, but also has low impedance and a high ion transport rate. When the composite solid electrolyte 300 is applied to a secondary battery, the secondary battery can have both a high energy density and good cycling performance. In addition, the composite solid electrolyte 300 of the embodiments of the present application has good lithium ion transport ability and good Li + selective permeability. When the composite solid electrolyte 300 is applied to a lithium extraction device, it is also conducive to improving the efficiency of lithium extraction from seawater.

[0089] In some embodiments of the present application, the transition layer 320 is formed by the mutual penetration of the first solid electrolyte layer 310 and the second solid electrolyte layer 330. Therefore, the transition layer 320 may include cross-linked poly(vinyl carbonate) in the first solid electrolyte layer 310 and polycarbonate compounds in the second solid electrolyte layer 330.

[0090] In some embodiments, the transition layer 320 may be a layer structure that is formed by the mutual penetration of the first solid electrolyte layer 310 and the second solid electrolyte layer 330 and is substantially uniform in terms of material composition. The transition layer 320 may also include a first lithium salt, an inorganic solid electrolyte, and a second lithium salt. When the transition layer 320 has the above composition, it can have good compatibility with the first solid electrolyte layer 310 and the second solid electrolyte layer 330, thereby enhancing the structural stability of the composite solid electrolyte 300. Thus, during the charge and discharge cycle process, the composite solid electrolyte can maintain an integrated structure, thereby maintaining low impedance and good ion transport rate, and further enhancing the cycling performance of the secondary battery.

[0091] In the embodiments of the present application, the polycarbonate compounds may include one or more of aliphatic polycarbonates, aliphatic-aromatic polycarbonates, and aromatic carbonates. Those skilled in the art can select appropriate polycarbonate compounds according to actual needs, and the embodiments of the present application do not limit this.

[0092] In a possible implementation, the polycarbonate compound may include at least one of poly(propylene carbonate) (PPC), poly(ethylene carbonate), and poly(trimethyl carbonate). The polycarbonate compound selected from the above types has good compatibility with crosslinked poly(vinylidene carbonate) and is not easily chemically reacted with crosslinked poly(vinylidene carbonate), which can further improve the ion transport rate of the composite solid electrolyte and improve the electrochemical stability inside the composite solid electrolyte. In addition, on the one hand, the polycarbonate compound selected from the above types is not easily electrochemically reacted with the negative electrode, which can improve the interfacial stability between the composite solid electrolyte and the negative electrode. On the other hand, the polycarbonate compound selected from the above types can undergo a microdecomposition reaction by itself to obtain a liquid decomposition product, and the liquid decomposition product can participate in the formation of the solid electrolyte interphase (SEI) in the negative electrode, thereby improving the stability of the negative electrode SEI.

[0093] In the embodiments of the present application, the first lithium salt and the second lithium salt may include the same substance or different substances. Exemplarily, the first lithium salt and the second lithium salt may each independently include one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis((trifluoromethyl)sulfonyl)azanide (LiTFSI), lithium trifluoromethanesulfonate, lithium tetrafluoroborate, lithium difluorobis(oxalato)phosphate, lithium bis(oxalato)borate (LiBOB), and lithium difluoro(oxalato)borate (LiDFOB).

[0094] In a possible implementation, the first lithium salt may include at least one of lithium bis((trifluoromethyl)sulfonyl)azanide (LiTFSI) and lithium difluoro(oxalato)borate (LiDFOB). LiTFSI and LiDFOB have high voltage stability, which can improve the antioxidant property of the first solid electrolyte layer. Thereby, the side reaction between the components in the first solid electrolyte layer and the positive electrode can be reduced, and the interfacial stability between the composite solid electrolyte and the positive electrode can be further improved.

[0095] In a possible implementation, the second lithium salt may include at least one of lithium bis((trifluoromethyl)sulfonyl)azanide (LiTFSI) and lithium bis(oxalato)borate (LiBOB). The second lithium salt can participate in the formation of the negative electrode SEI, and different types of the second lithium salt will form different types of SEI. When LiTFSI and LiBOB participate in the formation of the negative electrode SEI, the content of lithium fluoride (LiF) in the SEI can be increased. In this way, the SEI with a higher LiF content can have low impedance and good stability, which is beneficial to reducing the internal resistance of the secondary battery and improving the stability of the negative electrode environment. Thereby, the cycle performance of the secondary battery can be further improved.

[0096] In an embodiment of the present application, the inorganic solid electrolyte may be selected from inorganic solid electrolytes known in the art. Exemplarily, the inorganic solid electrolyte may include at least one of lithium germanium aluminum phosphate (LAGP), lithium titanium aluminum phosphate (LATP), lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), and lithium lanthanum zirconium titanium oxide (LLZTO).

[0097] Thus, LAGP, LATP, LLZO, and LLZTO are fast ion conductors and have high mechanical strength. When LAGP, LATP, LLZO, and LLZTO are dispersed in the second solid electrolyte layer, on the one hand, a fast ion transport channel can be formed to further improve the ion transport rate of the composite solid electrolyte. On the other hand, during the charging of the secondary battery, lithium ions may be unevenly deposited on the surface of the negative electrode, causing protrusions to form on the surface of the negative electrode. The electron and charge density at the protrusions are relatively large, resulting in more lithium ions preferentially depositing at the protrusions to form lithium dendrites. If the lithium dendrites continue to grow, they may pierce through the composite solid electrolyte layer and come into contact with the positive electrode, leading to an internal short circuit of the secondary battery, causing thermal runaway or even combustion and explosion of the secondary battery. LAGP, LATP, LLZO, and LLZTO can improve the mechanical strength of the second solid electrolyte layer, inhibit the growth of lithium dendrites at the negative electrode, and reduce the risk of lithium dendrites piercing through the composite solid electrolyte and contacting the positive electrode. In addition, LAGP, LATP, LLZO, and LLZTO have high reaction inertness with polycarbonate compounds and are not easily involved in side reactions with polycarbonate compounds, which is beneficial to improving the stability of the second solid electrolyte layer.

[0098] In addition, the inorganic solid electrolyte can be uniformly dispersed in the polycarbonate compound of the second solid electrolyte layer. On the one hand, the inorganic solid electrolyte is wrapped by the polycarbonate compound matrix, which can reduce the risk of side reactions of the inorganic solid electrolyte and improve the electrochemical stability of the second solid electrolyte layer. On the other hand, the inorganic solid electrolyte can effectively reduce the crystallinity of the polycarbonate compound, thereby further improving the ion transport rate of the second solid electrolyte layer.

[0099] In a possible implementation manner, a separator may be provided in the first solid electrolyte layer. Figure 4 The structural schematic diagram of the composite solid electrolyte provided by an embodiment of the present application is shown as Figure 4 shown. The separator 311 may be located between the surface of the first solid electrolyte layer 310 and the transition layer 320. The separator 311 may include a separator known in the art for secondary batteries. The separator 311 can provide certain support, improve the structural stability of the first solid electrolyte layer 310, and further improve the structural stability of the composite solid electrolyte.

[0100] The separator 311 may have a plurality of through-holes (not shown in the figure). The cross-linked poly(vinyl carbonate) and the first lithium salt may be filled in the through-holes to form a continuous ion transport channel inside the first solid electrolyte layer 310, and the continuous ion transport channel can shorten the ion transport path inside the first solid electrolyte layer 310. Thereby, the ion transport rate of the first solid electrolyte layer 310 can be improved.

[0101] In a possible implementation, the separator may include a cellulose membrane. On the one hand, the cellulose membrane has relatively large pores and a suitable porosity, and can accommodate more cross-linked poly(vinyl carbonate) and the first lithium salt. Thus, it is beneficial to form a continuous ion transport channel inside the separator, shorten the ion transport path inside the first solid electrolyte layer, and improve the ion transport rate of the first solid electrolyte layer. On the other hand, the cellulose membrane has high thermal stability and chemical stability, which is beneficial to improving the structural stability of the first solid electrolyte layer. In addition, the cellulose membrane also has the advantages of environmental friendliness, renewability, good biocompatibility, etc., and has good environmental protection performance.

[0102] It can be seen from the above implementation that the composite solid electrolyte of the embodiment of the present application can have high ionic conductivity. As an exemplary illustration, the ionic conductivity of the composite solid electrolyte can be 1×10 -4 S·cm -1 to 2×10 -4 S·cm -1 , specifically it can be 1×10 -4 S·cm -1 , 2×10 -4 S·cm -1 and any value between 1×10 -4 S·cm -1 and 2×10 -4 S·cm -1 , for example, it can be 1×10 -4 S·cm -1 , 1.2×10 -4 S·cm -1 , 1.5×10 -4 S·cm -1 , 1.8×10 -4 S·cm -1 , 2×10 -4 S·cm -1etc., which will not be listed one by one here. The ionic conductivity of the composite solid electrolyte has the meaning well known in the art. As an example, the ionic conductivity of the composite solid electrolyte can be measured by the alternating current impedance method, and the test temperature can be, for example, 55 °C. The ionic conductivity of the composite solid electrolyte can also be measured by other methods known in the art, and the embodiments of the present application do not limit this. When the ionic conductivity of the composite solid electrolyte is within the above range, the ionic transport rate in the electrochemical reaction can be effectively improved, thereby improving the cycling performance of the secondary battery. In addition, when the ionic conductivity of the composite solid electrolyte is within the above range, the efficiency of lithium extraction from seawater can be improved when it is subsequently applied to a lithium extraction device.

[0103] The embodiments of the present application also provide a preparation method of a composite solid electrolyte, including the following steps S10 to S40.

[0104] S10, prepare a crosslinked poly(vinyl carbonate) precursor.

[0105] The above crosslinked poly(vinyl carbonate) precursor may include raw materials for forming the first solid electrolyte layer. Exemplarily, the crosslinked poly(vinyl carbonate) precursor may include vinylene carbonate (VC), a first lithium salt, and an auxiliary agent required for forming the crosslinked poly(vinyl carbonate), wherein the auxiliary agent may include a crosslinking agent.

[0106] In some embodiments of the present application, in some embodiments, the auxiliary agent may further include at least one of an initiator and a catalyst. The first lithium salt may be selected from the first lithium salts used in any implementation manner of the composite solid electrolyte. The first lithium salt has been described in detail above and will not be repeated here.

[0107] S20, prepare a second solid electrolyte layer, and the second solid electrolyte layer includes a polycarbonate compound, an inorganic solid electrolyte, and a second lithium salt.

[0108] In some embodiments of the present application, the polycarbonate compound, the inorganic solid electrolyte, and the second lithium salt in the second solid electrolyte layer may be selected from the polycarbonate compounds, inorganic solid electrolytes, and second lithium salts used in any implementation manner of the composite solid electrolyte. The polycarbonate compounds, inorganic solid electrolytes, and second lithium salts have been described in detail above and will not be repeated here.

[0109] S30, contact the crosslinked poly(vinyl carbonate) precursor with the second solid electrolyte layer to obtain a composite solid electrolyte precursor.

[0110] In some embodiments of the present application, the crosslinked poly(vinyl carbonate) precursor has good interfacial compatibility with the second solid electrolyte layer. After the crosslinked poly(vinyl carbonate) precursor contacts the second solid electrolyte layer, the crosslinked poly(vinyl carbonate) precursor can dissolve the substances on the surface layer of the second solid electrolyte and penetrate each other with the second solid electrolyte layer to form a precursor transition layer, obtaining a composite solid electrolyte precursor without an obvious interlayer interface.

[0111] S40. Heat the composite solid electrolyte precursor to form the first solid electrolyte layer and the transition layer, obtaining the composite solid electrolyte.

[0112] Heat the composite solid electrolyte precursor prepared in steps S10 to S40 to form the first solid electrolyte layer and the transition layer, obtaining the composite solid electrolyte. Among them, the transition layer is located between the first solid electrolyte layer and the second solid electrolyte layer, and the transition layer is formed by the mutual penetration of the first solid electrolyte layer and the second solid electrolyte layer. The first solid electrolyte layer includes crosslinked poly(vinyl carbonate) and a first lithium salt.

[0113] In some embodiments of the present application, under heating conditions, the crosslinked poly(vinyl carbonate) precursor in the composite solid electrolyte precursor can undergo an in-situ polymerization reaction to obtain a mixture of crosslinked poly(vinyl carbonate) and a first lithium salt.

[0114] It should be noted that the temperature and duration of the in-situ polymerization reaction are not specifically limited, and those skilled in the art can adjust them according to the types of reactants, the degree of reaction progress, etc.

[0115] As an example, the reaction temperature can be from 60°C to 80°C, specifically can be 60°C, 80°C, and any value between 60°C and 80°C. For example, it can be 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, etc. The reaction duration can be from 8h to 12h, specifically can be 8h, 12h, and any value between 8h and 12h. For example, it can be 8h, 9h, 10h, 11h, 12h, etc. They are not listed one by one here.

[0116] It can be understood that the crosslinked poly(vinyl carbonate) precursor infiltrated in the precursor transition layer can undergo an in-situ polymerization reaction to obtain a transition layer including crosslinked poly(vinyl carbonate) and polycarbonate compounds.

[0117] On the one hand, both the transition layer and the first solid electrolyte layer are obtained by in-situ polymerization of vinylene carbonate in the cross-linked poly(vinylene carbonate) precursor with a cross-linking agent. The transition layer and the first solid electrolyte layer can form an integrated layer structure without an obvious interface. On the other hand, the precursor transition layer is formed by the mutual penetration of the cross-linked poly(vinylene carbonate) precursor and the second solid electrolyte layer. The precursor transition layer and the second solid electrolyte layer are continuously distributed. Thus, the formed transition layer is also continuously distributed with the second solid electrolyte layer, forming an integrated layer structure without an obvious interface. Therefore, the first solid electrolyte layer and the second solid electrolyte layer can form an integrated composite solid electrolyte through the transition layer. In the composite solid electrolyte, there is no obvious interface between the first solid electrolyte layer, the transition layer, and the second solid electrolyte layer, thereby significantly reducing the interfacial impedance of the composite solid electrolyte. In addition, in the composite solid electrolyte, the contact between the layer structures is uniform, and almost no voids are generated, which can effectively improve the ion transport rate between the layer structures, and further improve the ion transport rate of the composite solid electrolyte.

[0118] In a possible implementation manner, the above step S10 may specifically include the following steps S11 to S12.

[0119] S11, Mix the first lithium salt, vinylene carbonate, cross-linking agent, and initiator uniformly to obtain a precursor slurry.

[0120] In step S11, the cross-linking agent may include a cross-linking agent containing a carbon-carbon double bond. The cross-linking agent containing a carbon-carbon double bond may include, for example, at least one of ethoxylated trimethylolpropane triacrylate (ETPTA), pentaerythritol tetraacrylate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate. The cross-linking agent containing a carbon-carbon double bond can react with the carbon-carbon double bond in vinylene carbonate to form a cross-linked poly(vinylene carbonate) with a three-dimensional network structure. The initiator may include a radical initiator. Exemplarily, the initiator may be an azo initiator, for example, it may include at least one of azobisisobutyronitrile (AIBN) and azobis(isobutyric acid) dimethyl ester (AIBME). The initiator can decompose by heat to form primary radicals, thereby initiating the cross-linking reaction between vinylene carbonate and the cross-linking agent.

[0121] S12, Load the precursor slurry onto the separator to obtain a cross-linked poly(vinylene carbonate) precursor, wherein the separator has a plurality of through holes, and the precursor slurry is filled in the through holes.

[0122] In some embodiments of the present application, the separator can be used to accommodate the precursor slurry and inhibit the flow of the precursor slurry. Thus, after the crosslinked poly(vinylidene carbonate) precursor contacts the second solid electrolyte layer, the precursor slurry can penetrate to the surface layer of the second solid electrolyte layer without flowing to other positions, which is beneficial to the smooth progress of the in-situ polymerization reaction.

[0123] In an embodiment of the present application, the separator can include a separator for secondary batteries known in the art.

[0124] In a possible implementation, the separator can include a cellulose membrane. On the one hand, the cellulose membrane not only has large pores and a suitable porosity, but also has good affinity and wettability for the precursor slurry, which is beneficial to the precursor slurry being fully and uniformly infiltrated into the separator. In this way, after the subsequent in-situ polymerization reaction, the inside of the cellulose membrane can be uniformly filled with a mixture of crosslinked poly(vinylidene carbonate) and the first lithium salt, thereby forming a continuous ion transport channel. The continuous ion transport channel can shorten the ion transport path inside the first solid electrolyte layer, thereby improving the ion transport rate of the first solid electrolyte layer. On the other hand, the cellulose membrane has high thermal stability and chemical stability and is not easily reacted with the precursor slurry, which is beneficial to maintaining the structural stability of the first solid electrolyte layer. In addition, the cellulose membrane also has the advantages of environmental friendliness, renewability, good biocompatibility, etc., and has good environmental protection performance.

[0125] In a possible implementation, the mass ratio of vinylene carbonate to the crosslinking agent can be from 4:1 to 6:1. Specifically, the mass ratio of vinylene carbonate to the crosslinking agent can be 4:1, 6:1, and any value between 4:1 and 6:1, such as 4:1, 4.3:1, 4.5:1, 4.8:1, 5:1, 5.3:1, 5.5:1, 5.8:1, 6:1, etc. They are not listed one by one here.

[0126] Controlling the mass ratio of vinylene carbonate to the crosslinking agent within the above suitable range, on the one hand, poly(vinylidene carbonate) with a suitable crosslinking degree can be formed, so that the first solid electrolyte layer has both high mechanical strength and good flexibility. On the other hand, the poly(vinylidene carbonate) can contain more vinylene carbonate-derived structural units, and the vinylene carbonate-derived structural units can improve the ion transport rate of the crosslinked poly(vinylidene carbonate), thereby improving the ionic conductivity of the composite solid electrolyte.

[0127] In a possible implementation, the mass ratio of vinylene carbonate to the first lithium salt can be from 9:1 to 10:1. Specifically, the mass ratio of vinylene carbonate to the crosslinking agent can be 9:1, 10:1, and any value between 9:1 and 10:1. For example, it can be 9:1, 9.2:1, 9.4:1, 9.6:1, 9.8:1, 10:1, etc. They are not listed one by one here.

[0128] Controlling the mass ratio of vinylene carbonate to the first lithium salt within the above suitable range can, on the one hand, make the precursor slurry have good fluidity and permeability, which is conducive to the precursor slurry smoothly filling the through-holes of the separator and forming a continuous ion transport channel after in-situ polymerization reaction. The continuous ion transport channel can shorten the ion transport path inside the first solid electrolyte layer and improve the ion transport rate of the first solid electrolyte layer. On the other hand, it can make the first solid electrolyte layer contain more first lithium salts, thereby improving the ion transport rate of the first solid electrolyte layer. Furthermore, the ionic conductivity of the composite solid electrolyte is improved.

[0129] In a possible implementation, the mass ratio of vinylene carbonate to the initiator can be from 100:1 to 200:1. Specifically, the mass ratio of vinylene carbonate to the initiator can be 100:1, 200:1, and any value between 100:1 and 200:1. For example, it can be 100:1, 120:1, 150:1, 180:1, 200:1, etc. They are not listed one by one here. Controlling the mass ratio of vinylene carbonate to the initiator within the above suitable range is beneficial to improving the rate of the in-situ polymerization reaction.

[0130] In a possible implementation, the ratio of the volume of the precursor slurry to the area of the separator can be 8 μL·cm -2 to 12 μL·cm -2 . Specifically, the ratio of the volume of the precursor slurry to the area of the separator can be 8 μL·cm -2 , 12 μL·cm -2 and any value between 8 μL·cm -2 and 12 μL·cm -2 . For example, it can be 8 μL·cm -2 , 8.5 μL·cm -2 , 9 μL·cm -2 , 9.5 μL·cm -2 , 10 μL·cm -2 , 10.5 μL·cm -2 , 11 μL·cm -2 , 11.5 μL·cm -2 , 12 μL·cm -2 etc. They are not listed one by one here.

[0131] Controlling the ratio of the volume of the precursor slurry to the area of the separator within the above-mentioned appropriate range can load an appropriate amount of the precursor slurry on the separator, thereby forming a first solid electrolyte layer and a transition layer with appropriate thicknesses. The first solid electrolyte layer having an appropriate thickness can enable the first solid electrolyte layer to have a lower bulk impedance, thereby reducing the impedance of the composite solid electrolyte. The transition layer having an appropriate thickness can enhance the stability of the internal structure of the composite solid electrolyte, which is beneficial for the composite solid electrolyte to maintain a lower impedance and a higher ionic conductivity.

[0132] In some embodiments of the present application, during the process of preparing the second solid electrolyte layer in the above step S20, the contents of the polycarbonate compound, the inorganic solid electrolyte, and the second lithium salt can be adjusted according to actual needs.

[0133] In a possible implementation manner, the mass ratio of the polycarbonate compound to the inorganic solid electrolyte can be from 1:2 to 3:7. Specifically, the mass ratio of the polycarbonate compound to the inorganic solid electrolyte can be 1:2, 3:7, and any value between 1:2 and 3:7, such as 1:2, 7:15, 6:13, 5:11, 3:7, etc. They are not listed one by one here.

[0134] Controlling the mass ratio of the polycarbonate compound to the inorganic solid electrolyte within the above-mentioned appropriate range is beneficial for the uniform dispersion of the inorganic solid electrolyte in the polycarbonate compound matrix. Thus, not only can the inorganic solid electrolyte be connected through the polycarbonate compound matrix to form a continuous ion transport channel, but also the crystallinity of the polycarbonate compound matrix can be reduced, thereby enhancing the ion transport rate of the polycarbonate compound matrix. In addition, an appropriate content of the polycarbonate compound in the second solid electrolyte layer is also beneficial for enhancing the flexibility of the second solid electrolyte layer. Thus, not only can the processability of the second solid electrolyte layer be improved, but also the second solid electrolyte layer can be in close contact with the negative electrode, reducing the interfacial impedance between the second solid electrolyte and the negative electrode.

[0135] In a possible implementation manner, the mass ratio of the polycarbonate compound to the second lithium salt can be from 4:1 to 6:1. Specifically, the mass ratio of the polycarbonate compound to the inorganic solid electrolyte can be 4:1, 6:1, and any value between 4:1 and 6:1, such as 4:1, 4.5:1, 5:1, 5.5:1, 6:1, etc. They are not listed one by one here.

[0136] Controlling the mass ratio of the polycarbonate compound to the second lithium salt within a suitable range can enable the second solid electrolyte layer to contain a relatively large amount of the second lithium salt while having good flexibility, thereby enhancing the ion transport rate of the second solid electrolyte layer and further improving the ionic conductivity of the composite solid electrolyte.

[0137] In one possible implementation, step S20 above may specifically include the following steps S21 to S22.

[0138] S21, Dissolve the polycarbonate compound, the inorganic solid electrolyte, and the second lithium salt in an organic solvent to obtain a slurry for the second solid electrolyte layer.

[0139] Exemplarily, the organic solvent may include an organic solvent with certain volatility, such as, for example, but not limited to, at least one of N-methylpyrrolidone (NMP) and N,N-dimethylformamide (DMF).

[0140] S22, Place the slurry for the second solid electrolyte layer in a mold and remove the organic solvent to obtain the second solid electrolyte layer.

[0141] By preparing the second solid electrolyte layer through the above steps, the size of the second solid electrolyte layer can be flexibly adjusted, and the preparation efficiency of the composite solid electrolyte can be improved.

[0142] The embodiments of the present application do not limit the material of the mold, as long as it does not undergo side reactions with the components of the slurry for the second solid electrolyte layer. Exemplarily, the above mold may be a polytetrafluoroethylene mold. Polytetrafluoroethylene has excellent chemical stability and is not prone to side reactions with the components of the slurry for the second solid electrolyte layer. Moreover, polytetrafluoroethylene also has good non-stick properties and is not easily attached to the second solid electrolyte layer, which is beneficial to maintaining the flatness of the surface of the second solid electrolyte layer.

[0143] In the process of placing the slurry for the second solid electrolyte layer in a mold and removing the organic solvent, it may specifically include: placing the slurry for the second solid electrolyte layer in a mold and heating the mold to volatilize the organic solvent to remove the organic solvent.

[0144] In one possible implementation, the thickness of the slurry for the second solid electrolyte layer may be 200 μm to 300 μm. Specifically, the thickness of the slurry for the second solid electrolyte layer may be 200 μm, 300 μm, and any value between 200 μm and 300 μm, such as, for example, 200 μm, 220 μm, 250 μm, 280 μm, 300 μm, etc. They are not listed one by one here.

[0145] Controlling the thickness of the second solid electrolyte layer slurry within a suitable range is conducive to forming a second solid electrolyte layer with an appropriate thickness.

[0146] As an illustrative example, the above-mentioned second solid electrolyte layer slurry can form a second solid electrolyte layer with a thickness of 80 μm to 120 μm. Specifically, the thickness of the second solid electrolyte layer can be 80 μm, 120 μm, and any value between 80 μm and 120 μm. For example, it can be 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, etc. They are not listed one by one here.

[0147] Controlling the thickness of the second solid electrolyte layer within a suitable range can endow the second solid electrolyte layer with appropriate permeability. Furthermore, when the crosslinked poly(vinyl carbonate) precursor contacts the second solid electrolyte layer subsequently, the crosslinked poly(vinyl carbonate) precursor and the second solid electrolyte layer can penetrate each other to form a precursor transition layer with an appropriate thickness. Thus, the second solid electrolyte layer and the transition layer in the composite solid electrolyte can have appropriate thicknesses. The second solid electrolyte layer in the composite solid electrolyte having an appropriate thickness can inhibit the formation of lithium dendrites. The transition layer having an appropriate thickness can enhance the stability of the internal structure of the composite solid electrolyte, which is conducive to the composite solid electrolyte maintaining a low impedance and a high ionic conductivity.

[0148] As an illustrative example, the thickness of the composite solid electrolyte prepared according to the above implementation method can be 100 μm to 150 μm. Specifically, the thickness of the composite solid electrolyte can be 100 μm, 150 μm, and any value between 100 μm and 150 μm. For example, it can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, etc. They are not listed one by one here.

[0149] For example, the thickness of the second solid electrolyte layer can be 80 μm, and the thickness of the composite solid electrolyte can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, etc. For another example, the thickness of the second solid electrolyte layer can be 90 μm, and the thickness of the composite solid electrolyte can be 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, etc. For another example, the thickness of the second solid electrolyte layer can be 100 μm, and the thickness of the composite solid electrolyte can be 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, etc. For another example, the thickness of the second solid electrolyte layer can be 110 μm, and the thickness of the composite solid electrolyte can be 120 μm, 130 μm, 140 μm, 150 μm, etc. For another example, the thickness of the second solid electrolyte layer can be 120 μm, and the thickness of the composite solid electrolyte can be 130 μm, 140 μm, 150 μm, etc. They are not all listed here.

[0150] The composite solid electrolyte combining the above embodiments can be used to prepare secondary batteries. Exemplarily, the secondary battery can be prepared through the following steps S110 to S120.

[0151] S110, place the positive electrode, the composite solid electrolyte, and the negative electrode in sequence to obtain an electrode assembly.

[0152] Among them, the first solid electrolyte layer of the composite solid electrolyte is in contact with the positive electrode, and the second solid electrolyte layer is in contact with the negative electrode. This composite solid electrolyte is obtained according to the preparation method of the above composite solid electrolyte, and the specific preparation process is not elaborated here.

[0153] S120, perform hot pressing on the electrode assembly to obtain a secondary battery.

[0154] It can be understood that during the hot pressing process, the crosslinked poly(vinyl carbonate) on the surface of the first solid electrolyte layer and the polycarbonate compound on the surface of the second solid electrolyte layer both have a certain viscosity and can be bonded to the positive electrode and the negative electrode respectively.

[0155] It should be noted that the temperature and pressure of the hot pressing are not specifically limited. As an example, the hot pressing temperature can be from 60°C to 80°C, specifically 60°C, 80°C, and any value between 60°C and 80°C, such as 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, etc. The pressure of the hot pressing can be from 1 MPa to 4 MPa, specifically 1 MPa, 4 MPa, and any value between 1 MPa and 4 MPa, such as 1 MPa, 2 MPa, 3 MPa, 4 MPa, etc. They are not all listed here.

[0156] In a possible implementation, the secondary battery can also be prepared through the following steps S210 to S240.

[0157] S210, prepare a crosslinked poly(vinyl carbonate) precursor.

[0158] S220, prepare a second solid electrolyte layer, which includes a polycarbonate compound, an inorganic solid electrolyte, and a second lithium salt.

[0159] S230, stack the positive electrode, the crosslinked poly(vinyl carbonate) precursor, the second solid electrolyte layer, and the negative electrode in sequence to obtain an electrode assembly.

[0160] S240, heat the electrode assembly to form a first solid electrolyte layer and a transition layer, thereby obtaining the secondary battery.

[0161] In the secondary battery prepared according to steps S210 to S240, the crosslinked poly(vinyl carbonate) precursor and the second solid electrolyte layer can penetrate each other to form a precursor transition layer, which is then heated to form a transition layer. The transition layer is located between the first solid electrolyte layer and the second solid electrolyte layer, and the transition layer is formed by the mutual penetration of the first solid electrolyte layer and the second solid electrolyte layer. The first solid electrolyte layer includes crosslinked poly(vinyl carbonate) and a first lithium salt.

[0162] It can be understood that in the above implementation, the implementation manners of steps S210 and S220 are similar to those of steps S10 and S20, and will not be repeated here. In steps S230 and S240, after stacking the positive electrode, the crosslinked poly(vinyl carbonate) precursor, the second solid electrolyte layer, and the negative electrode in sequence, the precursor slurry in the crosslinked poly(vinyl carbonate) precursor can not only penetrate to the surface layer of the second solid electrolyte layer, but also penetrate into the gap between the crosslinked poly(vinyl carbonate) precursor and the positive electrode, and make full contact with the positive electrode.

[0163] During the heating process, vinylene carbonate and the crosslinking agent undergo an in-situ polymerization reaction. Similar to the formation process of the transition layer and the first solid electrolyte layer, the positive electrode and the first solid electrolyte layer can also form a layer structure with close contact and almost no voids through the in-situ polymerization reaction. Thereby, the interfacial contact between the composite solid electrolyte and the positive electrode can be improved, the interfacial impedance between the composite solid electrolyte and the positive electrode can be reduced, and the interfacial ion transport rate between the composite solid electrolyte and the positive electrode can be increased.

[0164] Step S240 can be adjusted according to actual needs. Exemplarily, the electrode assembly can be placed in a housing and then heated and sealed. It is also possible to heat the electrode assembly first, and then place the electrode assembly in the housing and seal it.

[0165] The composite solid electrolyte prepared by the above implementation method can also be used to prepare a lithium extraction device from seawater.

[0166] An embodiment of the present application also provides a lithium extraction device. As Figure 5 shown, this lithium extraction device can be used for lithium extraction from seawater. The lithium extraction device may include a positive electrode 510, a negative electrode 520, and a composite solid electrolyte 530. The composite solid electrolyte 530 is used to separate the positive electrode 510 and the negative electrode 520, and the composite solid electrolyte 530 does not contact the positive electrode 510 and the negative electrode 520. In the composite solid electrolyte 530, a first solid electrolyte layer (not shown in the figure) may face the negative electrode 520, and a second solid electrolyte layer (not shown in the figure) may face the positive electrode 510.

[0167] As an example, the positive electrode 510 of the lithium extraction device may include copper, and the negative electrode 520 of the lithium extraction device may include ruthenium.

[0168] When extracting lithium from seawater, a constant external current can be applied between the positive and negative electrodes. This constant external current can be applied through an external power source. The positive pole of the external power source can be connected to the negative electrode 520 of the lithium extraction device, and the negative pole of the external power source can be connected to the positive electrode 510 of the lithium extraction device. Seawater is continuously introduced into the area between the composite solid electrolyte 530 and the negative electrode 520. The negative electrode 520 can participate in the electrode reaction under the action of the external current, causing Li + to transfer to the positive electrode side of the lithium extraction device. The composite solid electrolyte 530 has selective permeability and can selectively permeate Li + in seawater and prevent other ions from permeating. After Li + passes through the composite solid electrolyte 530, it is enriched at the positive electrode 510 and is reduced to Li metal at the positive electrode 510, thereby realizing lithium extraction from seawater. The composite solid electrolyte of the embodiment of the present application has good lithium ion transmission ability and good Li + selective permeability, which is beneficial to improving the efficiency of lithium extraction from seawater.

[0169] The above composite solid electrolyte and the secondary battery containing the composite solid electrolyte are introduced below through specific embodiments. A secondary battery is prepared with the composite solid electrolyte prepared in the embodiments, and the performance of various secondary batteries is tested.

[0170] Example 1

[0171] In Example 1, a secondary battery was prepared according to the following steps.

[0172] Step 11: Prepare a crosslinked poly(vinyl carbonate) precursor. Specifically, dissolve 0.1688 g of LiTFSI in 1.6 g of VC and 0.35 g of ETPTA, stir for 3 h, add 0.0016 g of AIBN, and continue stirring for 30 min to obtain a precursor slurry. Drop the precursor slurry onto a cellulose separator with a diameter of 16 mm to obtain a crosslinked poly(vinyl carbonate) precursor.

[0173] Step 12: Prepare a second solid electrolyte layer. Specifically, add 0.15 g of LiTFSI, 0.75 g of PPC, and 1.5 g of LAGP to 3.2 mL of NMP, stir for 36 h to obtain a second solid electrolyte layer slurry; add the second solid electrolyte layer slurry to a polytetrafluoroethylene mold, and control the thickness of the second solid electrolyte layer slurry to be 300 μm; heat in vacuum at 80 °C for 24 h to remove NMP to obtain a second solid electrolyte layer with a thickness of 100 μm; take out the second solid electrolyte layer from the polytetrafluoroethylene mold, and punch it with a slicer to obtain a second solid electrolyte layer with a diameter of 16 mm.

[0174] Step 13: Stack the positive electrode, crosslinked poly(vinyl carbonate) precursor, second solid electrolyte layer, and negative lithium foil in sequence, place them in the case of a CR2025 button battery, and assemble a CR2025 button battery.

[0175] Exemplarily, in specific operation, the positive electrode is prepared by the following steps: Place 0.44 g of LiNi 0.6 Mn 0.2 Co 0.2 O2 (NCM622), 0.055 g of conductive carbon black (Super P), and 0.055 g of polyvinylidene fluoride (PVDF) in 1 mL of NMP, stir for 15 min and then coat it on a carbon-coated aluminum foil current collector, and dry at 80 °C for 12 h to obtain the positive electrode.

[0176] Step 14: Heat the CR2025 button battery at 70 °C for 12 h to obtain a secondary battery. Among them, the crosslinked poly(vinyl carbonate) precursor forms a first solid electrolyte layer and a transition layer under heating conditions. The transition layer is located between the first solid electrolyte layer and the second solid electrolyte layer, and the first solid electrolyte layer and the second solid electrolyte layer form an integrated composite solid electrolyte through the transition layer.

[0177] Example 2

[0178] In Example 2, a stainless steel (SS) / lithium (Li) battery is prepared according to the following steps.

[0179] Step 21: Prepare a crosslinked poly(vinyl carbonate) precursor. Specifically, dissolve 0.1688 g of LiTFSI in 1.6 g of VC and 0.35 g of ETPTA, stir for 3 h, add 0.0016 g of AIBN, and continue stirring for 30 min to obtain a precursor slurry. Drop the precursor slurry onto a cellulose separator with a diameter of 16 mm to obtain a crosslinked poly(vinyl carbonate) precursor.

[0180] Step 22: Prepare the second solid electrolyte layer. Specifically, add 0.15 g of LiTFSI, 0.75 g of PPC, and 1.5 g of LAGP to 3.2 mL of NMP, stir for 36 h to obtain a second solid electrolyte layer slurry; add the second solid electrolyte layer slurry to a polytetrafluoroethylene mold, and control the thickness of the second solid electrolyte layer slurry to be 300 μm; heat in vacuum at 80 °C for 24 h to remove NMP, and obtain a second solid electrolyte layer with a thickness of 100 μm; take out the second solid electrolyte layer from the polytetrafluoroethylene mold, and punch it with a slicing machine to obtain a second solid electrolyte layer with a diameter of 16 mm.

[0181] Step 23: Stack the positive electrode, the crosslinked poly(vinyl carbonate) precursor, the second solid electrolyte layer, and the negative lithium foil in sequence, place them in the case of a CR2025 button battery, and assemble a CR2025 button battery.

[0182] Exemplarily, in specific operation, the positive electrode is prepared by the following steps: ultrasonically clean the SS with a diameter of 16 mm in deionized water and absolute ethanol in sequence, and polish the cleaned SS smooth with 800-mesh sandpaper to obtain an SS positive electrode.

[0183] Step 24: Heat the CR2025 button battery at 70 °C for 12 h to obtain an SS / Li battery. Among them, the crosslinked poly(vinyl carbonate) precursor forms a first solid electrolyte layer and a transition layer under heating conditions. The transition layer is located between the first solid electrolyte layer and the second solid electrolyte layer, and the first solid electrolyte layer and the second solid electrolyte layer form an integrated composite solid electrolyte through the transition layer.

[0184] Comparative Example 1

[0185] In Comparative Example 1, a secondary battery is prepared according to the following steps.

[0186] Step 31: Prepare a crosslinked poly(vinyl carbonate) precursor. Specifically, dissolve 0.1688 g of LiTFSI in 1.6 g of VC and 0.35 g of ETPTA, stir for 3 h, add 0.0016 g of AIBN, and continue stirring for 30 min to obtain a precursor slurry. Drop the precursor slurry onto a cellulose separator with a diameter of 16 mm to obtain a crosslinked poly(vinyl carbonate) precursor.

[0187] Step 32: Stack the positive electrode, the crosslinked poly(vinyl carbonate) precursor, and the negative lithium foil in sequence, place them in the casing of a CR2025 button cell, and assemble them into a CR2025 button cell.

[0188] Exemplarily, in specific operation, the positive electrode is prepared through the following steps: Place 0.44 g of NCM622, 0.055 g of SuperP, and 0.055 g of PVDF in 1 mL of NMP, stir for 15 min, then coat it on a carbon-coated aluminum foil current collector, and dry it at 80 °C for 12 h to obtain the positive electrode.

[0189] Step 33: Heat the CR2025 button cell at 70 °C for 12 h to obtain a secondary battery. Among them, the crosslinked poly(vinyl carbonate) precursor forms a first solid electrolyte layer under heating conditions.

[0190] Comparative Example 2

[0191] In Comparative Example 2, a secondary battery is prepared according to the following steps.

[0192] Step 41: Prepare a second solid electrolyte layer. Specifically, add 0.15 g of LiTFSI, 0.75 g of PPC, and 1.5 g of LAGP to 3.2 mL of NMP, stir for 36 h to obtain a second solid electrolyte layer slurry; add the second solid electrolyte layer slurry to a polytetrafluoroethylene mold, and control the thickness of the second solid electrolyte layer slurry to be 300 μm; vacuum heat it at 80 °C for 24 h to remove NMP, and obtain a second solid electrolyte layer with a thickness of 100 μm; take out the second solid electrolyte layer from the polytetrafluoroethylene mold, and punch it with a slicing machine to obtain a second solid electrolyte layer with a diameter of 16 mm.

[0193] Step 42: Stack the positive electrode, the second solid electrolyte layer, and the negative lithium foil in sequence, place them in the casing of a CR2025 button cell, and assemble to obtain a secondary battery.

[0194] Exemplarily, in specific operation, the positive electrode is prepared through the following steps: Place 0.44 g of NCM622, 0.055 g of SuperP, and 0.055 g of PVDF in 1 mL of NMP, stir for 15 min, then coat it on a carbon-coated aluminum foil current collector, and dry it at 80 °C for 12 h to obtain the positive electrode.

[0195] Comparative Example 3

[0196] In Comparative Example 3, an SS / Li battery is prepared according to the following steps.

[0197] Step 51: Prepare a crosslinked poly(vinyl carbonate) precursor. Specifically, dissolve 0.1688 g of LiTFSI in 1.6 g of VC and 0.35 g of ETPTA, stir for 3 h, add 0.0016 g of AIBN, and continue stirring for 30 min to obtain a precursor slurry. Drop the precursor slurry onto a cellulose separator with a diameter of 16 mm to obtain a crosslinked poly(vinyl carbonate) precursor.

[0198] Step 52: Stack the positive electrode, the crosslinked poly(vinyl carbonate) precursor, and the negative lithium foil in sequence, place them in the housing of a CR2025 coin cell, and assemble a CR2025 coin cell.

[0199] Exemplarily, in specific operation, the positive electrode is prepared through the following steps: ultrasonically clean SS in deionized water and absolute ethanol in sequence, and polish the cleaned SS smoothly with 800-mesh sandpaper to obtain an SS positive electrode.

[0200] Step 53: Heat the CR2025 coin cell at 70 °C for 12 h to obtain an SS / Li battery. Among them, the crosslinked poly(vinyl carbonate) precursor forms a first solid electrolyte layer under heating conditions.

[0201] Comparative Example 4

[0202] In Comparative Example 4, a secondary battery is prepared according to the following steps.

[0203] Step 61: Prepare a crosslinked poly(vinyl carbonate) precursor. Specifically, dissolve 0.1688 g of LiTFSI in 1.6 g of VC and 0.35 g of ETPTA, stir for 3 h, add 0.0016 g of AIBN, and continue stirring for 30 min to obtain a precursor slurry. Drop the precursor slurry onto a cellulose separator with a diameter of 16 mm to obtain a crosslinked poly(vinyl carbonate) precursor.

[0204] Step 62: Prepare a second solid electrolyte layer. Specifically, add 0.15 g of LiTFSI, 0.75 g of PPC, and 1.5 g of LAGP to 3.2 mL of NMP, stir for 36 h to obtain a second solid electrolyte layer slurry; add the second solid electrolyte layer slurry to a polytetrafluoroethylene mold, and control the thickness of the second solid electrolyte layer slurry to be 300 μm; heat in vacuum at 80 °C for 24 h to remove NMP to obtain a second solid electrolyte layer with a thickness of 100 μm; take out the second solid electrolyte layer from the polytetrafluoroethylene mold, and punch it with a slicing machine to obtain a second solid electrolyte layer with a diameter of 16 mm.

[0205] Step 63: Place the crosslinked poly(vinyl carbonate) precursor on the surface of the positive electrode, and heat at 70 °C for 12 h to obtain a composite structure of the positive electrode and the first solid electrolyte layer.

[0206] Exemplarily, during specific operations, the positive electrode is prepared through the following steps: 0.44 g of NCM622, 0.055 g of SuperP, and 0.055 g of PVDF are placed in 1 mL of NMP, stirred for 15 min, and then coated on a carbon-coated aluminum foil current collector, and dried at 80 °C for 12 h to obtain the positive electrode.

[0207] Step 64: The positive electrode / first solid electrolyte layer composite structure, the second solid electrolyte layer, and the negative lithium foil are stacked in sequence and placed in the housing of a CR2025 button battery to assemble a secondary battery. Among them, the first solid electrolyte layer is in contact with the second solid electrolyte layer to obtain a composite solid electrolyte.

[0208] Performance tests are respectively carried out on the secondary batteries prepared in the above Examples 1-2 and Comparative Examples 1-4.

[0209] Specifically, the secondary battery of Example 1 is disassembled to obtain a composite solid electrolyte. Scanning electron microscope (SEM) images of the surface of the first solid electrolyte layer and the surface of the second solid electrolyte layer in the composite solid electrolyte are respectively taken, and X-ray diffraction (XRD) tests are carried out on the second solid electrolyte layer.

[0210] Figure 6 is the SEM image of the surface of the first solid electrolyte layer. From Figure 6 It can be observed that crosslinked poly(vinylidene carbonate) undergoes in-situ polymerization in the pores of the separator to form continuous lithium-ion transport channels. It can be understood that the continuous lithium-ion transport channels can shorten the ion transport path inside the first solid electrolyte layer, improve the ion transport rate of the first solid electrolyte layer, and thus improve the ion transport rate of the composite solid electrolyte.

[0211] Figure 7 is the SEM image of the surface of the second solid electrolyte layer. From Figure 7 It can be observed that inorganic solid electrolyte LAGP particles are uniformly dispersed in the PPC matrix. It can be understood that the uniform dispersion of LAGP particles in the PPC matrix can not only reduce the risk of side reactions of the inorganic solid electrolyte and improve the electrochemical stability of the second solid electrolyte layer, but also effectively reduce the crystallinity of PPC, thereby further improving the ion transport rate of the second solid electrolyte layer. Figure 8 is the XRD pattern of the composite solid electrolyte. Further combined with Figure 8 It can be found that the composite solid electrolyte exhibits an obvious LiGe2(PO4)3 crystal phase, and at the same time, the characteristic broad peak representing the polymer in PPC disappears, verifying the decrease in the crystallinity of PPC.

[0212] In addition, charge-discharge cycle tests were carried out on Example 1 and Comparative Examples 1-2. Specifically, the secondary batteries prepared in Example 1 and Comparative Examples 1-2 were subjected to charge-discharge cycle tests at a charge-discharge rate of 0.1C / 0.1C, and the voltage range was 3.0V to 4.2V. The charge capacity and discharge capacity of each cycle were recorded. Based on the charge capacity and discharge capacity of each cycle, the cycle capacity retention rate and Coulomb efficiency of each cycle can be calculated respectively. Among them, the cycle capacity retention rate of the nth cycle = (discharge capacity of the nth cycle / discharge capacity of the first cycle) × 100%; the Coulomb efficiency of the nth cycle = (discharge capacity of the nth cycle / charge capacity of the nth cycle) × 100%.

[0213] Figure 9 is the discharge capacity - cycle number graph of Example 1 and Comparative Examples 1-2. From Figure 9 it can be observed that the secondary battery of Comparative Example 1 short-circuited after 20 cycles and could not continue to be charged and discharged. The cycle capacity retention rate of the secondary battery of Comparative Example 2 decreased to 70.7% after 60 cycles. While the cycle capacity retention rate of the secondary battery of Example 1 increased to 83.8% after 60 cycles, which was much higher than that of Comparative Example 2.

[0214] Figure 10 is the Coulomb efficiency - cycle number graph of Example 1 and Comparative Examples 1-2. From Figure 10 it can be observed that the Coulomb efficiency of Comparative Example 1 decreased rapidly with the increase of the cycle number, and the Coulomb efficiency at 20 cycles was only 58.3%, indicating that serious side reactions occurred inside the secondary battery. The average Coulomb efficiency of Comparative Example 2 was 99.2%. In contrast, the average Coulomb efficiency of Example 1 was 99.3%, indicating a further improvement in cycle stability.

[0215] Combined with Figure 9 and Figure 10 it can be verified that the composite solid electrolyte of the embodiments of the present application can significantly improve the cycle performance of secondary batteries.

[0216] In addition, linear sweep voltammetry (LSV) tests were carried out on the SS / Li batteries of Example 2 and Comparative Example 3. Specifically, the test voltage range was 0 - 5.5V, and the scanning rate was 1mV / s, and the LSV test graph as shown in Figure 11 was obtained. From Figure 11It can be observed that in the LSV test curve of Comparative Example 3, an oxidation current appears in the first solid electrolyte layer near 1.1 V, indicating that the first solid electrolyte layer reacts with Li of the negative electrode. An oxidation peak also appears in the LSV test curve of Comparative Example 3 near 4.5 V, indicating that the first solid electrolyte layer reacts with the positive electrode. It can be found that the electrochemical window of the first solid electrolyte layer in Comparative Example 3 is relatively narrow, only 1.1 V - 4.5 V. Compared with Comparative Example 3, the electrochemical window of the composite solid electrolyte in Example 2 can be widened to 0 - 5 V, indicating that the composite solid electrolyte has good interfacial stability with both the positive electrode and the negative electrode.

[0217] In addition, the secondary batteries of Example 1 and Comparative Example 4 were tested by electrochemical impedance spectroscopy (EIS), and the EIS test graph as shown in Figure 12 was obtained. From Figure 12 it can be observed that the impedance of Comparative Example 4 is 12473 Ω, and the impedance of Example 1 is only 515 Ω. By analyzing the test results of Comparative Example 4 and Example 1, it can be found that in the composite solid electrolyte obtained by the direct physical contact of the first solid electrolyte layer and the second solid electrolyte layer, the interfacial contact between the first solid electrolyte layer and the second solid electrolyte layer is very poor, and the interfacial impedance is extremely high. Therefore, the overall impedance of the composite solid electrolyte is also very high; while in the composite solid electrolyte prepared by in-situ polymerization, the first solid electrolyte layer and the second solid electrolyte layer are an integrated structure, which significantly reduces the interfacial impedance inside the composite solid electrolyte, thereby reducing the impedance of the composite solid electrolyte.

[0218] Based on the secondary battery provided by the embodiments of the present application, the embodiments of the present application also provide a battery system. The battery system includes a battery module, and the battery module may include a plurality of secondary batteries provided by the embodiments of the present application.

[0219] The battery module can be obtained by connecting a plurality of secondary batteries in series, parallel or in a series-parallel combination. The secondary battery can be used as the energy storage and output unit in the battery system. The series-parallel combination refers to a structural method of wire connection with both series and parallel connections. In some embodiments, the battery module may include a housing, and the housing can play a role in supporting, fixing and protecting the secondary battery.

[0220] Figure 13 is a schematic structural diagram of the battery system provided by the embodiments of the present application. As shown in Figure 13 In some embodiments of the present application, the battery system may further include a battery management system. The battery management system can be used for intelligent management and maintenance of each secondary battery unit, monitor the state of the secondary battery, and prevent the secondary battery from overcharging and over-discharging to extend the service life of the secondary battery.

[0221] Based on the secondary battery provided by the embodiments of the present application, the embodiments of the present application further provide an electronic device, including a charge-discharge circuit and a power-consuming component, and further including the secondary battery provided by the present application. The secondary battery is connected to the charge-discharge circuit and is charged through the charge-discharge circuit or supplies power to the power-consuming component.

[0222] In some embodiments of the present application, the above-mentioned electronic device may include, but is not limited to, devices such as mobile phones, tablet computers, laptop computers, ultra-mobile personal computers (UMPCs), netbooks, personal digital assistants (PDAs), wearable devices, vehicle-mounted devices, smart home devices, artificial intelligence (AI) devices, etc.

[0223] In a possible implementation manner, the electronic device may be an electric vehicle, and the secondary battery may be assembled with other components into a battery system for supplying power to the electric vehicle.

[0224] The above-described embodiments of the present application do not constitute a limitation on the protection scope of the present invention.

[0225] In some solutions, multiple embodiments of the present application may be combined and the combined solution may be implemented. Optionally, some operations in the processes of the method embodiments are optionally combined, and / or the order of some operations is optionally changed. And, the execution order between the steps of each process is only exemplary and does not constitute a limitation on the execution order between the steps. The steps may also be in other execution orders. It is not intended to indicate that the execution order is the only order in which these operations can be performed.

[0226] Those of ordinary skill in the art will think of various ways to reorder the operations described in the embodiments of the present application. In addition, it should be noted that the process details involved in a certain embodiment of the present application are also applicable to other embodiments in a similar manner, or different embodiments may be combined and used.

[0227] In addition, some steps in the method embodiments may be equivalently replaced with other possible steps. Or, some steps in the method embodiments may be optional and may be deleted in some usage scenarios. Or, other possible steps may be added in the method embodiments.

[0228] Moreover, each method embodiment can be implemented independently or in combination. The above content is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any change or replacement within the technical scope disclosed in the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A composite solid electrolyte, characterized in that, Comprising: A first solid electrolyte layer, a transition layer, and a second solid electrolyte layer, the transition layer being located between the first solid electrolyte layer and the second solid electrolyte layer, and the transition layer being formed by the mutual penetration of the first solid electrolyte layer and the second solid electrolyte layer; The first solid electrolyte layer comprises crosslinked poly(vinyl carbonate) and a first lithium salt; The second solid electrolyte layer comprises a polycarbonate compound, an inorganic solid electrolyte, and a second lithium salt.

2. The composite solid electrolyte according to claim 1, characterized in that, The transition layer comprises the crosslinked poly(vinyl carbonate), the first lithium salt, the polycarbonate compound, the inorganic solid electrolyte, and the second lithium salt.

3. The composite solid electrolyte according to claim 1 or 2, characterized in that, A separator is provided in the first solid electrolyte layer, the separator having a plurality of through holes, and the crosslinked poly(vinyl carbonate) and the first lithium salt are filled in the through holes.

4. The composite solid electrolyte according to any one of claims 1 - 3, characterized in that, The ionic conductivity of the composite solid electrolyte is 1×10 -4 S·cm -1 to 2×10 -4 S·cm -1 .

5. The composite solid electrolyte according to any one of claims 1 - 4, characterized in that, The polycarbonate compound comprises at least one of poly(propylene carbonate), poly(ethylene carbonate), and poly(trimethyl carbonate).

6. The composite solid electrolyte according to claim 3, characterized in that, The separator comprises a cellulose membrane.

7. The composite solid electrolyte according to any one of claims 1 - 6, characterized in that, The inorganic solid electrolyte comprises at least one of lithium germanium aluminum phosphate, lithium titanium aluminum phosphate, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium titanium oxide.

8. The composite solid electrolyte according to any one of claims 1 - 7, characterized in that, The first lithium salt comprises at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalato)borate.

9. The composite solid electrolyte according to any one of claims 1 - 8, characterized in that, The second lithium salt comprises at least one of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(oxalato)borate.

10. A method for preparing a composite solid electrolyte, characterized in that, Comprising: Preparing a crosslinked poly(vinyl carbonate) precursor; Preparing a second solid electrolyte layer, the second solid electrolyte layer comprising a polycarbonate compound, an inorganic solid electrolyte, and a second lithium salt; Bringing the crosslinked poly(vinyl carbonate) precursor into contact with the second solid electrolyte layer to obtain a composite solid electrolyte precursor; Heating the composite solid electrolyte precursor to form a first solid electrolyte layer and a transition layer, thereby obtaining a composite solid electrolyte; wherein, the transition layer is located between the first solid electrolyte layer and the second solid electrolyte layer, and the transition layer is formed by the mutual penetration of the first solid electrolyte layer and the second solid electrolyte layer; the first solid electrolyte layer comprises crosslinked poly(vinyl carbonate) and a first lithium salt.

11. The preparation method according to claim 10, characterized in that, The preparing of the crosslinked poly(vinyl carbonate) precursor comprises: Mixing the first lithium salt, vinyl carbonate, a crosslinking agent, and an initiator uniformly to obtain a precursor slurry; Loading the precursor slurry onto a separator to obtain the crosslinked poly(vinyl carbonate) precursor, wherein the separator has a plurality of through holes, and the precursor slurry is filled in the through holes.

12. The preparation method according to claim 11, characterized in that, The mass ratio of the vinyl carbonate to the crosslinking agent is 4:1 to 6:1; the mass ratio of the vinyl carbonate to the first lithium salt is 9:1 to 10:

1.

13. The preparation method according to claim 11 or 12, characterized in that, The ratio of the volume of the precursor slurry to the area of the separator is 8 μL·cm -2 to 12 μL·cm -2 .

14. The preparation method according to any one of claims 10 - 13, characterized in that, The mass ratio of the polycarbonate compound to the inorganic solid electrolyte is 1:2 to 3:7; the mass ratio of the polycarbonate compound to the second lithium salt is 4:1 to 6:

1.

15. The preparation method according to any one of claims 10 - 14, characterized in that, The preparing of the second solid electrolyte layer comprises: Dissolving the polycarbonate compound, the inorganic solid electrolyte, and the second lithium salt in an organic solvent to obtain a second solid electrolyte layer slurry; Place the second solid electrolyte layer slurry in a mold and remove the organic solvent to obtain the second solid electrolyte layer.

16. The preparation method according to claim 15, characterized in that, The thickness of the second solid electrolyte layer slurry is 200 μm to 300 μm.

17. The preparation method according to any one of claims 10 - 16, characterized in that, The thickness of the second solid electrolyte layer is 80 μm to 120 μm.

18. A secondary battery, characterized in that, Comprising a positive electrode, a negative electrode, and the composite solid electrolyte according to any one of claims 1-9, the composite solid electrolyte is filled between the positive electrode and the negative electrode, the first solid electrolyte layer is in contact with the positive electrode, and the second solid electrolyte layer is in contact with the negative electrode.

19. The secondary battery according to claim 18, characterized in that, The positive electrode comprises a nickel-cobalt-manganese ternary positive electrode material, and the negative electrode comprises metallic lithium or a lithium alloy.

20. A preparation method of a secondary battery, characterized in that, Comprising: Prepare a crosslinked poly(vinyl carbonate) precursor; Prepare a second solid electrolyte layer, the second solid electrolyte layer comprising a polycarbonate compound, an inorganic solid electrolyte, and a second lithium salt; Stack the positive electrode, the crosslinked poly(vinyl carbonate) precursor, the second solid electrolyte layer, and the negative electrode in sequence to obtain an electrode assembly; Heat the electrode assembly to form a first solid electrolyte layer and a transition layer to obtain a secondary battery; wherein the transition layer is located between the first solid electrolyte layer and the second solid electrolyte layer, and the transition layer is formed by mutual penetration of the first solid electrolyte layer and the second solid electrolyte layer; the first solid electrolyte layer comprises crosslinked poly(vinyl carbonate) and a first lithium salt.

21. A battery system, characterized in that, Comprising a battery module, the battery module comprising a plurality of secondary batteries according to claim 18 or 19.

22. An electronic device, characterized in that, The electronic device comprises a housing, and electronic components and a battery accommodated in the housing, the battery powers the electronic components, and the battery comprises the secondary battery according to claim 18 or 19.

23. A lithium extraction device, characterized in that, Comprising a positive electrode, a negative electrode, and the composite solid electrolyte according to any one of claims 1-9, the composite solid electrolyte is used to separate the positive electrode and the negative electrode, and the composite solid electrolyte is not in contact with the positive electrode and the negative electrode; The first solid electrolyte layer faces the negative electrode, and the second solid electrolyte layer faces the positive electrode.

Images