Positive plate and lithium ion battery

Abstract

The invention discloses a positive plate and a lithium ion battery, relates to the technical field of lithium ion batteries, and aims to solve the problem that metal ions are deposited on a negative electrode due to dissolution of metal on a positive electrode material in the lithium ion battery. The positive plate comprises a positive electrode material layer and a cation exchange membrane. The cation exchange membrane is arranged on the surface of the positive electrode material layer; the cation exchange membrane comprises a parent group, a monovalent anion connected with the parent group, and a monovalent cation, the parent group comprises a molecular chain cross-linked network.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a positive electrode sheet and a lithium-ion battery. Background Art

[0002] There is metal dissolution in the positive electrode material of lithium-ion batteries. The dissolved metal ions are easily deposited at the negative electrode, which intensifies the negative electrode side reactions, consumes the active lithium in the electrolyte, and blocks the lithium ion channel, resulting in battery capacity decay. Summary of the invention

[0003] The purpose of the present application is to provide a positive electrode sheet and a lithium-ion battery, aiming to solve the problem of metal dissolution on the positive electrode material in the lithium-ion battery, causing metal ions to be deposited on the negative electrode.

[0004] In order to achieve the above objectives, this application adopts the following technical solutions:

[0005] In a first aspect, the present application provides a positive electrode sheet. The positive electrode sheet comprises: a positive electrode material layer and a cation exchange membrane. The cation exchange membrane is arranged on the surface of the positive electrode material layer.

[0006] The cation exchange membrane includes: monovalent anions and monovalent cations connected by parent groups, and the parent groups include a molecular chain cross-linked network.

[0007] In the positive electrode sheet provided in the embodiment of the present application, first, the molecular chain of the parent group in the cation exchange membrane has a cross-linked three-dimensional network structure, which limits the movement of the molecular chain, making it difficult for the parent group to dissolve in the solvent, and can ensure that the cation exchange membrane can remain stable during the charge and discharge process. The monovalent anion is connected to the parent group to form a fixed charge in the cation exchange.

[0008] Secondly, monovalent cations can move freely in the cation exchange membrane and form a dynamic equilibrium with monovalent anions. The monovalent cations and monovalent anions attract each other, so that the cation exchange membrane only allows monovalent cations to pass through, while other high-valent metal cations cannot pass through the cation exchange membrane. In other words, the cation exchange membrane allows lithium ions to migrate between the positive and negative electrodes, and prevents other high-valent metal ions (such as Fe 2+ The metal ions dissolved from the positive electrode sheet cannot be deposited on the surface of the negative electrode sheet, thereby reducing the metal deposition on the negative electrode, reducing the negative electrode side reaction, and reducing the consumption of active lithium in the electrolyte, thereby improving the capacity retention rate of the lithium-ion battery.

[0009] At the same time, it can also prevent high-valent metal ions from dissolving into the electrolyte, reduce the high-valent metal ions from passing through the SEI membrane (a solid electrolyte interface membrane formed on the surface of the negative electrode), and deposit on the negative electrode sheet, avoiding the negative impact of high-valent metal ions destroying the SEI membrane and protecting the performance and life of the lithium-ion battery.

[0010] In some embodiments, the monovalent cation comprises: a dissociable monovalent cation.

[0011] In some embodiments, the dissociable monovalent cations include at least one of lithium ions and sodium ions.

[0012] In some embodiments, the monovalent anion comprises: sulfonate.

[0013] In some embodiments, the parent group comprises: a resin.

[0014] In some embodiments, the resin includes at least one of polyethylene resin, polystyrene resin, polypropylene resin, polyvinyl chloride resin, phenolic resin, epoxy resin, polytetrafluoroethylene resin, and silicone resin.

[0015] In some embodiments, the parent group is linked to the monovalent anion by a chemical bond.

[0016] In some embodiments, the conductivity of the cation exchange membrane is in the range of 0.01 S / cm to 0.1 S / cm.

[0017] In some embodiments, the material of the positive electrode material layer includes: lithium iron phosphate.

[0018] In a second aspect, the present application provides a lithium-ion battery. The lithium-ion battery comprises: a negative electrode sheet and a positive electrode sheet as described in any one of the above embodiments.

[0019] The positive electrode sheet and the negative electrode sheet are arranged opposite to each other, and the cation exchange membrane of the positive electrode sheet is located on the side of the positive electrode material layer of the positive electrode sheet facing the negative electrode sheet.

[0020] It can be understood that the beneficial effects that can be achieved by the lithium-ion battery provided in the above embodiments of the present application can refer to the beneficial effects of the positive electrode sheet mentioned above, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1A schematic diagram of a lithium-ion battery provided for some embodiments;

[0023] Figure 2 A schematic diagram of a lithium-ion battery provided for some embodiments;

[0024] Figure 3 A schematic diagram of a positive electrode sheet provided in some embodiments;

[0025] Figure 4 This is a diagram of the capacity retention rate of Experimental Examples 3 and 4.

[0026] Figure numerals: 1-positive electrode sheet, 2-negative electrode sheet, 3-diaphragm, 4-cation exchange membrane, 5-positive electrode material layer. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0028] In the description of this application, it should be understood that the terms "upper", "lower", etc. indicate positions or positional relationships based on the positions or relative positional relationships shown in the accompanying drawings, which are only for the convenience of describing this application and simplifying the description, and therefore cannot be understood as limiting this application. Unless otherwise specified, the above-mentioned directional descriptions can be flexibly set in the actual application process under the condition that the relative positional relationships shown in the accompanying drawings are met.

[0029] In the description of the present application, unless otherwise specified, “plurality” means two or more.

[0030] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense, for example, it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meaning of the above terms in this application can be understood according to specific circumstances.

[0031] In the present application, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, article or device including the element.

[0032] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0033] In the description of this specification, specific features, structures, materials or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0034] Lithium-ion battery (Lithium-ion Battery) is a secondary battery (rechargeable battery) with high energy density, good cycle life and low self-discharge rate. It is widely used in consumer electronics (such as mobile phones, tablets, laptops, etc.), electric vehicles (such as electric vehicles, hybrid vehicles and electric bicycles, etc.), renewable energy storage (such as energy storage for solar and wind power generation systems) and portable tools (such as power tools and gardening tools, etc.).

[0035] Lithium-ion batteries achieve charging and discharging through the movement of lithium ions between the positive and negative electrodes. When charging, lithium ions are deintercalated from the positive electrode and embedded into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; the opposite is true when discharging.

[0036] The embodiment of the present application provides a lithium ion battery. Figure 1 and Figure 2 As shown, the lithium-ion battery includes: a negative electrode sheet 2 and a positive electrode sheet 1.

[0037] In some examples, the lithium-ion battery further includes: an electrolyte and a separator 3 .

[0038] The electrolyte is usually a liquid or solid ion conductive material (such as an electrolyte) that allows lithium ions to migrate between the negative electrode sheet 2 and the positive electrode sheet 1 while preventing direct conduction of electrons, thereby avoiding internal short circuits in the battery.

[0039] The separator 3 is located between the positive electrode sheet 1 and the negative electrode sheet 2 to prevent the positive electrode sheet 1 and the negative electrode sheet 2 from directly contacting each other and causing a short circuit, while allowing lithium ions in the electrolyte to pass through.

[0040] It can be understood that the negative electrode sheet 2 is located on the negative electrode of the lithium-ion battery; and the positive electrode sheet 2 is located on the positive electrode of the lithium-ion battery.

[0041] The main function of the negative electrode sheet 2 is to store lithium ions and release these lithium ions into the electrolyte during discharge.

[0042] Illustratively, the negative electrode sheet 2 includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is coated on the surface of the negative electrode current collector.

[0043] For example, the material of the negative electrode current collector may be copper.

[0044] For example, the active material on the negative electrode sheet 2 may be a carbon material (such as graphite) or a silicon-based composite material.

[0045] The positive electrode sheet 1 receives lithium ions migrated from the negative electrode sheet 2 during charging, and releases lithium ions back into the electrolyte during discharging, generating current through an external circuit. The positive electrode sheet 1 includes a positive electrode material, which stores and releases lithium ions during charging and discharging.

[0046] Exemplarily, the positive electrode sheet 1 includes: a positive electrode current collector, a positive electrode material, a binder, a conductive agent, etc., which are not limited here.

[0047] In some exemplary embodiments, the positive electrode current collector may be in the form of a metal foil or a mesh.

[0048] For example, the material of the positive electrode current collector may be aluminum.

[0049] In some embodiments, the positive electrode material includes: lithium iron phosphate.

[0050] Understandably, the use of lithium iron phosphate as the positive electrode material can enable lithium-ion batteries to maintain good performance in high temperature environments and long-term use, and can withstand high temperatures of 350°C to 500°C; theoretically, the cycle life of lithium-ion batteries can reach more than 2,000 times, and even more than 3,000 times with 95% capacity; due to the strong chemical bond binding force of phosphate groups, stable structure, and not easy to release oxygen, compared with lithium cobalt oxide and lithium manganese oxide batteries, lithium iron phosphate batteries will not explode under strong collisions. Therefore, the use of lithium iron phosphate as the positive electrode material can make lithium-ion batteries safer. The use of lithium iron phosphate as the positive electrode material can enable lithium-ion batteries to maintain good working performance at different temperatures, and its operating temperature range is wide, for example, the temperature range is -20°C to 75°C.

[0051] However, there is a phenomenon of metal dissolution in the positive electrode material of lithium-ion batteries. At the same time, the high temperature environment and small particle size of lithium metal oxides will further aggravate this phenomenon. The dissolved metals mainly include Fe 2+ / Fe 3+ , Mn 4+ 、Co 3+ 、Ti 4+ Sn 2+ and V 2+ / V 3+The dissolved metal ions are easily deposited at the negative electrode, causing the side reactions of the graphite negative electrode to intensify, consuming the active lithium in the electrolyte, and blocking the lithium ion channel, resulting in the capacity decay of the lithium-ion battery.

[0052] In addition, the reaction of water in the electrolyte with the positive electrode material (such as LiPF6) or the decomposition of the positive electrode material (such as LiPF6) itself will produce HF, H + Attacking the cathode material will result in metal dissolution.

[0053] In some examples, methods for inhibiting the dissolution of metal ions, such as adding an iron chelating agent, are used to inhibit the dissolution of metal ions. 2+ / Fe 3+ The chelating agent reacts with the electrolyte to convert it into a solid and prevent it from being deposited on the surface of the negative electrode 2. However, the amount of chelating agent added to the electrolyte is small, and the Fe dissolved in the electrolyte cannot be effectively removed. 2+ / Fe 3+ , resulting in many Fe 2+ / Fe 3+ Still able to deposit on the negative electrode surface.

[0054] Based on this, Figure 1 and Figure 3 As shown, the positive electrode sheet 1 comprises: a positive electrode material layer 5 and a cation exchange membrane 4. The cation exchange membrane 4 is arranged on the surface of the positive electrode material layer 5.

[0055] The cation exchange membrane 4 includes: monovalent anions and monovalent cations connected by parent groups. The parent groups include a molecular chain cross-linking network.

[0056] As described above, the positive electrode material can reversibly embed and extract lithium ions, thereby realizing the charging and discharging of lithium-ion batteries. However, the metal ions on the positive electrode material are dissolved, causing the metal ions to be deposited on the negative electrode.

[0057] The cation exchange membrane 4 is a functional polymer membrane that selectively allows cations to pass through while blocking the passage of anions and other molecules, while blocking the direct flow of electrons to avoid short circuits.

[0058] The molecular chains of the parent groups in the cation exchange membrane 4 have a cross-linked three-dimensional network structure, which restricts the movement of the molecular chains and makes it difficult for the parent groups to dissolve in the solvent. It is like a huge, interconnected network that is difficult for solvent molecules to break apart.

[0059] In addition, there may be some strong chemical bonds in the parent group, such as covalent bonds. These chemical bonds can ensure strong interactions between the molecular chains, and the molecular chains are not easily destroyed by solvent molecules, making them difficult to dissolve. In addition, strong intermolecular forces such as hydrogen bonds will be formed between some parent groups, which also helps to maintain the overall structural stability of the polymer matrix and prevent dissolution.

[0060] Therefore, the parent group is the structural basis of the cation exchange membrane 4, determines the mechanical properties and chemical stability of the cation exchange membrane 4, and ensures that the cation exchange membrane 4 can remain stable during the charge and discharge process.

[0061] The monovalent anions are connected to the parent groups, forming fixed charges in the cation exchange membrane 4. The monovalent cations can move freely in the cation exchange membrane 4, forming a dynamic equilibrium with the monovalent anions, and the monovalent cations and the monovalent anions attract each other, so that the cation exchange membrane 4 only allows monovalent cations to pass through, and other high-valent metal cations cannot pass through the cation exchange membrane 4. Figure 1 As shown, that is, the cation exchange membrane 4 allows lithium ions to migrate between the positive electrode sheet 1 and the negative electrode sheet 2, preventing other high-valent metal ions (such as Fe 2+ The metal ions dissolved from the positive electrode sheet 1 cannot be deposited on the surface of the negative electrode sheet 2, thereby reducing the metal deposition on the negative electrode, reducing the negative electrode side reaction, and reducing the consumption of active lithium in the electrolyte, thereby improving the capacity retention rate of the lithium-ion battery.

[0062] At the same time, it can also prevent high-valent metal ions from dissolving into the electrolyte, reduce the high-valent metal ions from passing through the SEI film (a layer of solid electrolyte interface film formed on the surface of the negative electrode), and deposit on the negative electrode sheet 2, avoiding the negative impact of high-valent metal ions destroying the SEI film and protecting the performance and life of the lithium-ion battery.

[0063] In some embodiments, the monovalent cation comprises: a dissociable monovalent cation.

[0064] It can be understood that the monovalent cation is an ion with a positive charge, which can move freely in the electrolyte of the battery and participate in the electrochemical reaction of the battery. The dissociable monovalent cations can be effectively dissociated in the cation exchange membrane 4 and participate in the ions of the conductivity, making it easier for the dissociable monovalent cations to migrate between the positive and negative electrodes, and more efficiently embed and de-embed during the charge and discharge process, ensuring the storage and release performance of the lithium-ion battery.

[0065] In some embodiments, the dissociable monovalent cations include at least one of lithium ions and sodium ions.

[0066] Understandably, both lithium ions and sodium ions are ions with a positive charge, and can effectively move between the positive and negative electrodes of lithium-ion batteries during the charging and discharging process, ensuring good power output and charging efficiency of lithium-ion batteries. In addition, lithium ions have high energy density and are suitable for high-performance devices; while sodium ions have low cost and abundant sodium resources, making them suitable for large-scale energy storage.

[0067] In some embodiments, the monovalent anion comprises: sulfonate.

[0068] It can be understood that after the sulfonate radical is connected to the parent group, the cation exchange membrane 4 carries a negative charge. Due to the principle that like charges repel each other, the cation exchange membrane 4 can repel anions and only allow cations with a positive charge (such as lithium ions and sodium ions) to pass through. At the same time, due to the hydrophilicity and ionization ability of the sulfonate radical, it helps to enhance the selective permeability of the cation exchange membrane 4, making it easier for monovalent cations to pass through the cation exchange membrane 4.

[0069] Moreover, the sulfonate group has good acid and alkali resistance and chemical stability, which enables the cation exchange membrane 4 to maintain long-term stability and effectiveness in the electrolyte, thereby maintaining the overall performance of the lithium-ion battery.

[0070] In some embodiments, the parent group comprises: a resin.

[0071] It can be understood that the resin, as a parent group, provides the necessary mechanical strength and structural stability for the cation exchange membrane 4, making the membrane not easy to break or deform, and maintaining the integrity and function of the membrane. In addition, the resin usually contains ion exchange sites (such as sulfonic acid groups) inside, and these sites exchange charges with cations (such as lithium ions or sodium ions) to form effective ion migration channels, reduce lithium ion migration resistance, and ensure the performance of lithium ion batteries.

[0072] In some embodiments, the resin includes at least one of polyethylene resin, polystyrene resin, polypropylene resin, polyvinyl chloride resin, phenolic resin, epoxy resin, polytetrafluoroethylene resin, and silicone resin.

[0073] Polyethylene resin (PE) has good water resistance, chemical stability, mechanical strength, and good flexibility, and can enhance the rigidity and stability of the cation exchange membrane 4 .

[0074] Polypropylene resin (PP) has high strength and rigidity, as well as good chemical resistance and heat resistance, and can improve the mechanical properties of the cation exchange membrane 4 .

[0075] Polyvinyl chloride resin (PVC) has good chemical resistance, rigidity and excellent acid and alkali resistance, and can improve the selectivity and mechanical strength of the cation exchange membrane 4 .

[0076] Phenolic resin has excellent heat resistance, chemical resistance and mechanical strength, high hardness and small shrinkage, and can be used as a reinforcing material to improve the overall structure and durability of the cation exchange membrane 4, while also helping to increase the electrical insulation of the membrane.

[0077] Epoxy resin has excellent bonding strength, chemical resistance and mechanical strength, improves the structural stability and durability of the cation exchange membrane 4, and may also improve the ion conductivity.

[0078] Polytetrafluoroethylene resin (PTFE) has excellent chemical stability, high temperature resistance and low friction characteristics, and may provide a good ion conduction path while improving the anti-fouling ability of the cation exchange membrane 4 .

[0079] The organic silicon resin has excellent weather resistance, high temperature resistance and excellent electrical insulation performance, and improves the service life of the cation exchange membrane 4 .

[0080] Polystyrene resin (PS) has good tolerance and can be used as a substrate for the cation exchange membrane 4 to provide good structural strength and integrity.

[0081] The above-mentioned resins each have different physical and chemical properties. In the cation exchange membrane 4, the advantages of the above-mentioned resins can be utilized in different ways. Selecting a suitable resin or a combination thereof can help improve the mechanical strength, chemical stability and ionic conductivity of the cation exchange membrane 4, thereby improving the overall performance and application effect of the cation exchange membrane 4.

[0082] In some embodiments, the parent group is linked to the monovalent anion by a chemical bond.

[0083] It can be understood that the monovalent anions are connected by chemical bonds, which enhances the overall structural stability of the cation exchange membrane 4, thereby improving the cycle stability and life of the lithium-ion battery.

[0084] Illustratively, the sulfonate group undergoes an electrophilic substitution reaction with the benzene ring on the polystyrene chain. During the reaction, the hydrogen atoms on the benzene ring are replaced by sulfonic acid groups, so that the sulfonate group is connected to the polymer skeleton of the polystyrene resin by a covalent bond, allowing the sulfonate group to exist relatively stably in the polystyrene resin structure.

[0085] In some embodiments, the conductivity of the cation exchange membrane 4 is in the range of 0.01 S / cm to 0.1 S / cm.

[0086] For example, the conductivity of the cation exchange membrane 4 may be 0.01 S / cm, 0.02 S / cm, 0.04 S / cm, 0.016 S / cm, 0.06 S / cm, 0.08 S / cm or 0.1 S / cm, etc., which is not limited here.

[0087] It can be understood that the conductivity of the cation exchange membrane 4 can reflect the difficulty of lithium ions migrating in the cation exchange membrane 4. The higher the conductivity, the easier it is for lithium ions to conduct in the cation exchange membrane 4, which is beneficial to improving the ion exchange efficiency and electrochemical performance of the cation exchange membrane 4. The above-mentioned setting can make the dissociation degree of monovalent cations larger, the monovalent cations are more ionized, and can effectively promote the conduction of monovalent cations, thereby improving the ion exchange efficiency and electrochemical performance of the cation exchange membrane 4.

[0088] In some embodiments, the positive electrode sheet 1 and the negative electrode sheet 2 are arranged opposite to each other, and the cation exchange membrane 4 of the positive electrode sheet 1 is located on the side of the positive electrode material layer 5 of the positive electrode sheet 1 facing the negative electrode sheet 2 .

[0089] It can be understood that setting the cation exchange membrane 4 of the positive electrode sheet 1 on the side of the positive electrode material layer 5 of the positive electrode sheet 1 facing the negative electrode sheet 2 can effectively reduce the movement of the metal phase dissolved from the positive electrode material to the negative electrode sheet 2, so that the metal ions cannot be deposited on the negative electrode surface, thereby reducing the deposition of metal at the negative electrode, reducing the negative electrode side reactions, and reducing the consumption of active lithium in the electrolyte, thereby improving the capacity retention rate of the lithium-ion battery.

[0090] The following is a further detailed description using specific experimental examples as examples.

[0091] Experimental Example 1

[0092] Experimental Example 1 provides a positive electrode sheet 1. The positive electrode sheet 1 includes a positive electrode material layer 5 and a cation exchange membrane 4. The positive electrode material is lithium iron phosphate. The cation exchange membrane 4 is arranged on the surface of the positive electrode material layer 5. The parent group of the cation exchange membrane 4 is polyvinyl fluoride, the monovalent anion is sulfonate, and the monovalent cation is lithium ion.

[0093] Experimental Example 2

[0094] Experimental Example 2 provides a positive electrode sheet 1. The positive electrode sheet 1 includes a positive electrode material, and the positive electrode material is lithium iron phosphate.

[0095] Experimental Example 3

[0096] Experimental Example 3 provides a lithium-ion battery. The lithium-ion battery is formed into a small soft-pack lithium-ion battery by laminating 8 layers of negative electrode sheets 2, 7 layers of positive electrode sheets 1 and a separator 3. Among them, the positive electrode sheet 1 includes a positive electrode material layer 5 and a cation exchange membrane 4. The positive electrode material is lithium iron phosphate. The cation exchange membrane 4 is arranged on the surface of the positive electrode material layer 5. The parent group of the cation exchange membrane 4 is polyvinyl fluoride, the monovalent anion is sulfonate, and the monovalent cation is lithium ion.

[0097] Experimental Example 4

[0098] Experimental Example 4 provides a lithium-ion battery. The lithium-ion battery is formed into a small soft-pack lithium-ion battery by laminating 8 layers of negative electrode sheets 2, 7 layers of positive electrode sheets 1 and a separator 3. The positive electrode sheet 1 includes a positive electrode material layer 5, and the positive electrode material is lithium iron phosphate.

[0099] Performance Testing

[0100] Test 1: The positive electrode sheets 1 of Experimental Example 1 and Experimental Example 2 were placed in electrolyte and ultrapure water, respectively, and the iron ion content in the electrolyte and ultrapure water was tested by ICP, as follows:

[0101] Add 1000ppm of water to 500g of electrolyte and let it stand at room temperature for one day. The acidity is tested to be 1648ppm. Take 100g of electrolyte and put it in a beaker. Take 5g of positive electrode sheet 1 of Experimental Example 1 and Experimental Example 2 respectively, soak them in the beaker for 1 day, then take out the positive electrode sheet 1, and then place it in a beaker filled with 100g of ultrapure water and soak it for 0.5h respectively. Test the iron ion content in the electrolyte and the ultrapure water supernatant. Repeat the above operation 5 times. The results are shown in Table 1.

[0102] Table 1 Iron ions (Fe) of positive electrode sheet 1 in electrolyte and ultrapure water of Experimental Example 1 and Experimental Example 2 3+ )content

[0103]

[0104]

[0105] It should be noted that the ultrapure water is used to soak out the iron ions dissolved from the positive electrode sheet 1 to characterize the total amount of iron dissolved. Secondly, it is to illustrate that the positive electrode sheets 1 of Experimental Examples 1 and 2 both have iron dissolved in the electrolyte containing water, and the content is almost the same, that is, the sum of the iron ion content in the first column and the iron ion content in the third column in Table 1 ≈ the sum of the iron ion content in the second column and the iron ion content in the fourth column.

[0106] As shown in Table 1, the iron ion content of the positive electrode sheet 1 of Experimental Example 1 in the electrolyte is significantly less than that of the positive electrode sheet 1 of Experimental Example 2. This is because the positive electrode sheet 1 of Experimental Example 1 is provided with a cation exchange membrane 4, which makes the high-valent metal ion Fe 3+ It cannot pass through the cation exchange membrane 4 into the electrolyte.

[0107] Test 2: The lithium-ion batteries of Experimental Examples 3 and 4 were placed in a 60°C environment and cycled 300 times at a current of 1C to test their capacity retention. The results are as follows: Figure 4 shown.

[0108] Depend on Figure 4It can be seen that the capacity retention rate of the lithium-ion battery in Experimental Example 3 is 81.52%; the capacity retention rate of the lithium-ion battery in Experimental Example 4 is 75.14%. The capacity decay of the lithium-ion battery in Experimental Example 4 is relatively large. This is because the iron ions on the positive electrode sheet 1 of the lithium-ion battery in Experimental Example 4 are mostly dissolved, and the migration to the negative electrode sheet 2 consumes active lithium, which makes the capacity decay of the lithium-ion battery in Experimental Example 4 relatively large. Therefore, the capacity retention rate of Experimental Example 4 is relatively low. The positive electrode sheet 1 of the lithium-ion battery in Experimental Example 3 is provided with a cation exchange membrane 4, so that the iron ions on the positive electrode sheet 1 are mostly dissolved and cannot migrate to the negative electrode sheet 2, so that the capacity decay of the lithium-ion battery in Experimental Example 3 is relatively small, thereby improving the capacity retention rate of the lithium-ion battery.

[0109] Test 3: After Test 2 was completed, the lithium-ion batteries of Experimental Examples 3 and 4 were disassembled, the negative electrode sheet 2 was taken out, and the iron ion content was tested by ICP after rinsing. The results are shown in Table 2.

[0110] Table 2 Iron ions (Fe) of negative electrode sheet 2 of Experimental Examples 3 and 4 3+ )content

[0111]

[0112]

[0113] It can be seen from Table 2 that the iron ion content of the negative electrode sheet 2 of the lithium ion battery of Experimental Example 3 is less than that of the negative electrode sheet 2 of the lithium ion battery of Experimental Example 4, indicating that the lithium ion battery of Experimental Example 3 has less iron ions migrating from the positive electrode sheet 1 to the negative electrode sheet 2. This is because the cation exchange membrane 4 set on the positive electrode sheet 1 of the lithium ion battery of Experimental Example 3 makes it impossible for high-valent metal ions to pass through the cation exchange membrane 4 and migrate to the negative electrode sheet 2.

[0114] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A positive electrode sheet, characterized in that: include: A positive electrode material layer; A cation exchange membrane, disposed on the surface of the positive electrode material layer; Wherein, the cation exchange membrane comprises: a parent group, monovalent anions connected to the parent group, and monovalent cations; the parent group comprises a molecular chain cross-linked network.

2. The positive electrode sheet according to claim 1, characterized in that: The monovalent cations include: dissociable monovalent cations.

3. The positive electrode sheet according to claim 2, characterized in that: The dissociable monovalent cations include at least one of lithium ions and sodium ions.

4. The positive electrode sheet according to claim 1, characterized in that: The monovalent anions include sulfonate.

5. The positive electrode sheet according to claim 1, characterized in that: The parent group includes: resin.

6. The positive electrode sheet according to claim 5, characterized in that: The resin includes at least one of polyethylene resin, polystyrene resin, polypropylene resin, polyvinyl chloride resin, phenolic resin, epoxy resin, polytetrafluoroethylene resin and silicone resin.

7. The positive electrode sheet according to claim 1, characterized in that: The parent group is connected to the monovalent anion via a chemical bond.

8. The positive electrode sheet according to claim 1, characterized in that: The conductivity of the cation exchange membrane ranges from 0.01 S / cm to 0.1 S / cm.

9. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: The material of the positive electrode material layer includes: lithium iron phosphate.

10. A lithium ion battery, characterized in that: include: A negative electrode sheet and a positive electrode sheet as claimed in any one of claims 1 to 9; The positive electrode sheet and the negative electrode sheet are arranged opposite to each other, and the cation exchange membrane of the positive electrode sheet is located on the side of the positive electrode material layer of the positive electrode sheet facing the negative electrode sheet.

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