Anti-overcharge sodium ion battery positive plate

Abstract

The invention discloses an anti-overcharge sodium ion battery positive plate which comprises a positive active material, a conductive agent, a binder and an anti-overcharge additive, and the anti-overcharge additive is aromatic sodium carboxylate. The anti-overcharge sodium ion battery positive plate has the characteristics of good anti-overcharge effect, excellent electrochemical performance and high safety.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion batteries, and in particular to an anti-overcharge type sodium ion battery positive electrode sheet. Background Art

[0002] With the rise of the energy revolution, secondary batteries have attracted widespread attention as a new energy storage method. Sodium-ion batteries (SIBs) are considered to be an ideal alternative to lithium-ion batteries (LIBs) due to their abundant resources, low cost, good low-temperature performance, superior rate performance and high safety. However, the initial Coulombic efficiency of the positive electrode material of SIBs is low, resulting in the irreversible consumption of the limited Na+ in the positive electrode, which in turn affects the reversible capacity and energy density of the full battery.

[0003] In sodium-ion batteries, overcharge protection is an important consideration for the safety performance of SIBs. Overcharging can lead to increased internal pressure in the battery and may even cause thermal runaway and explosion. Therefore, the development of effective overcharge protectors is crucial to improve the safety of SIBs.

[0004] Overcharge protection additives usually prevent battery overcharge based on their own redox reactions. The main mechanism is the redox shuttle effect: some additives do not participate in the reaction under normal battery charge and discharge, but when the battery charging voltage exceeds the cut-off voltage and reaches the oxidation potential of the additive, the additive molecules lose electrons at the positive electrode to form free radical molecules. These free radical molecules diffuse to the negative electrode to undergo electron reduction, forming a current loop, consuming the applied current, and achieving the effect of stabilizing the external voltage. Formation of a protective film: Commonly used additives such as 3-chloroanisole (3CA) and dimethoxydiphenylsilane (DDS) form a polymer film on the electrode surface during overcharge, which increases the internal resistance of the battery and delays the voltage rise during overcharge, thereby suppressing voltage runaway and achieving internal protection of the battery from overcharge.

[0005] Anti-overcharge additives are introduced into the battery system to ensure that they can effectively prevent thermal runaway and explosion risks when the battery is overcharged. However, since overcharge protection agents often do not participate in electrochemical reactions at low voltages, although they increase the safety of the battery, they will reduce the battery energy density. Therefore, it is imperative to develop multifunctional anti-overcharge additives. Summary of the invention

[0006] The purpose of the present invention is to provide an anti-overcharge type sodium ion battery positive electrode sheet, which has the characteristics of good anti-overcharge effect, excellent electrochemical performance and high safety.

[0007] The present invention can be implemented by the following technical solutions: The invention discloses an anti-overcharge type sodium ion battery positive electrode sheet, comprising a positive electrode active material, a conductive agent, a binder and an anti-overcharge additive, wherein the anti-overcharge additive is an aromatic sodium carboxylate.

[0008] Furthermore, the sodium aromatic carboxylate is sodium naphthyl aromatic carboxylate and biphenyl aromatic carboxylate in a molar ratio of 10:1-100.

[0009] In the present invention, the chemical formula of the sodium aromatic carboxylate is sodium naphthyl aromatic carboxylate C 10+n H 8-n O 2n Na n (4≥n≥2) and sodium biphenyl aromatic carboxylate C 12+n H 10-n O 2n Na n (6≥n≥2), n is the number of substitutions of the sodium carboxylate in the aromatic structure. If the number is less than 2, the theoretical specific capacity is too low and the sodium supplementation effect is too poor. However, due to the large steric hindrance, it is difficult to obtain more than 6 sodium carboxylates in the aromatic structure.

[0010] In the aromatic sodium carboxylates of the present invention, the molar ratio of sodium naphthyl aromatic carboxylates and sodium biphenyl aromatic carboxylates is 10:1-100, including but not limited to 10:1, 10:10, 10:90, 10:100 and other ratios. Because from the perspective of spatial structure, biphenyl is a non-planar structure, and the number of substitutions of sodium carboxylate derivatives on the aromatic ring of biphenyl is higher, so a sodium biphenyl aromatic carboxylate with a higher specific capacity can be obtained. Naphthalene is a planar structure. When sodium carboxylate replaces hydrogen on the aromatic ring of naphthalene, it faces greater steric hindrance, and it is difficult to obtain sodium naphthyl aromatic carboxylates with more than four substitutions. Also due to the steric hindrance effect, the oxidative polymerization potential of naphthalene is lower. According to these two characteristics, the ratio of the two sodium aromatic carboxylates can be adjusted according to demand. Increasing the ratio of sodium biphenyl aromatic carboxylates can obtain a higher overcharge threshold voltage, and increasing the ratio of polysubstituted sodium biphenyl aromatic carboxylates can more effectively improve energy density and efficiency.

[0011] Further, the sodium naphthyl aromatic carboxylate is sodium 1,4,5,8-naphthalenetetracarboxylate and / or sodium 2,3,6,7-naphthalenetetracarboxylate. With the planar polycyclic aromatic hydrocarbon naphthalene as the substrate, multiple sodium carboxylate functional groups are introduced on the aromatic ring. Due to steric hindrance, the number of introduced functional groups is 2-4. The additive mainly undergoes two electrochemical reactions in the positive electrode. The first is decarboxylation and desodiumation at low pressure. The released active sodium ions can compensate for the irreversible loss of sodium ions in the battery. The second is electro-oxidative polymerization. As the overcharge proceeds, the naphthalene after decarboxylation and desodiumation undergoes electro-oxidative polymerization to form a conductive polymer layer with high resistance. The polymer layer can prevent further escape and embedding of sodium ions. At the same time, the growing polymer layer will gradually conduct the positive and negative electrodes, and the voltage is kept within the safe voltage range through self-discharge. The planar junction of naphthalene has a higher electron density and a more stable electron cloud distribution. The mobility and stability of this electron may make the molecules with planar structure more active during oxidative polymerization, and also make its oxidative polymerization potential lower.

[0012] Furthermore, the sodium biphenyl aromatic carboxylate is one or more of sodium 4,4'-biphenyldicarboxylate, sodium 3,3',4,4'-biphenyltetramethylate, sodium 2,3,3',4'-biphenyltetracarboxylate, and sodium biphenyl-3,3',4,4',5',5'-hexacarboxylate. Taking the non-planar polycyclic aromatic hydrocarbon biphenyl as the substrate, multiple sodium carboxylate functional groups are introduced on the aromatic ring. Biphenyl is a non-planar structure, and the number of introduced functional groups is 2 to 6. The additive mainly undergoes two electrochemical reactions in the positive electrode. The first is decarboxylation and desodiumation at low pressure. The released active sodium ions can compensate for the irreversible loss of sodium ions in the battery. The second is electro-oxidative polymerization. As the overcharge proceeds, the biphenyl after decarboxylation and desodiumation undergoes electro-oxidative polymerization to form a conductive polymer layer with high resistance. This polymer layer can prevent the further escape and embedding of sodium ions. At the same time, the growing polymer layer will gradually connect the positive and negative electrodes, and the voltage is kept within the safe voltage range through self-discharge. In contrast to naphthalene, the non-planar structure of biphenyl has a higher potential for oxidative polymerization.

[0013] Furthermore, the positive electrode active material is a polyanion positive electrode material, a Prussian blue positive electrode material or a layered oxide positive electrode material. The additive is compatible with a variety of positive electrode materials. During the first week of charging and the positive electrode de-sodiumization process, the additive undergoes decarboxylation and de-sodiumization. The product after decarboxylation and de-sodiumization does not participate in the electrochemical reaction during the normal charging and discharging process.

[0014] Furthermore, the polyanion positive electrode materials are sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7), sodium vanadium phosphate (Na3V2(PO4)3), sodium iron sulfate (Na2Fe(SO4)2), sodium manganese titanium phosphate, tunnel phase Na 0.44 MnO2, layered Na 0.67 MnO2, Na 0.67 Ni 0.33 Mn 0.67 One or more of O2.

[0015] Furthermore, the binder is one or more of tetrafluoroethylene, polytetrafluoroethylene, sodium carboxymethyl cellulose, polyacrylic acid, Furthermore, the conductive agent is one or more of super P, acetylene black, Ketjen black, and carbon nanotubes.

[0016] Furthermore, the positive electrode sheet is coated on a positive electrode current collector, and the positive electrode current collector is a copper foil or an aluminum foil.

[0017] Furthermore, in the positive electrode sheet, the weight ratio of the positive electrode active material, the conductive agent, the binder and the anti-overcharge additive is 70-90:10-20:10-20:0.01-20. Specifically, the higher the amount of the aromatic sodium carboxylate added, the higher the decomposition and replenishment capacity, but due to its relatively poor conductivity, adding too much will reduce the electrochemical performance of the battery.

[0018] The present invention discloses an anti-overcharge type sodium ion battery positive electrode sheet, which has the following beneficial effects: First, the anti-overcharge effect is good. The sodium ion battery positive electrode of the present invention is added with an anti-overcharge additive, aromatic sodium carboxylate. The additive has good air stability. Due to the adjustment of its molecular structure and the increase of electron cloud density, its carboxylic acid group is easier to dissociate, and has a lower oxidation decomposition voltage than ordinary sodium carboxylate; Second, the electrochemical performance is excellent. The sodium ion battery positive electrode sheet of the present invention is added with an aromatic sodium carboxylate additive, which has a high sodium supplement capacity. Due to its low decomposition voltage, its utilization efficiency is higher than 95%. The carboxyl group on the aromatic ring can be designed as required to obtain a sodium supplement with a high theoretical capacity, making the aromatic sodium carboxylate a more effective sodium supplement additive, which helps to improve the energy density and performance of the sodium ion battery. Even with a 5% addition, the first week charging capacity of the sodium ion battery is increased by more than 14.5 mAh / g; Third, high safety. After adding the anti-overcharge additive to the positive electrode sheet of the sodium ion battery of the present invention, the safety of the sodium ion battery is greatly improved. The overcharge threshold voltage can be expanded to 4.5V-4.8V by adjusting the ratio of the aromatic sodium carboxylate, that is, the decomposition products of the aromatic sodium carboxylate undergo electrochemical polymerization at high voltage (within the range of 4.5V-4.8V), forming a conductive film on the cathode surface, and the polymer deposits may develop to penetrate the isolation film to reach the anode surface, thereby causing an internal short circuit. At the same time, the conductive polymer increases the internal resistance of the battery to limit the overcharge current, so that the overcharged battery automatically discharges to a safer charging state. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention is further described in detail below in conjunction with embodiments.

[0020] The invention discloses an anti-overcharge type sodium ion battery positive electrode sheet, comprising a positive electrode active material, a conductive agent, a binder and an anti-overcharge additive, wherein the anti-overcharge additive is an aromatic sodium carboxylate.

[0021] Furthermore, the sodium aromatic carboxylate is sodium naphthyl aromatic carboxylate and biphenyl aromatic carboxylate in a molar ratio of 10:1-100.

[0022] Furthermore, the sodium naphthyl aromatic carboxylate is sodium 1,4,5,8-naphthalenetetracarboxylate and / or sodium 2,3,6,7-naphthalenetetracarboxylate.

[0023] Furthermore, the sodium biphenyl aromatic carboxylate is one or more of sodium 4,4'-biphenyldicarboxylate, sodium 3,3',4,4'-biphenyltetramethylate, sodium 2,3,3',4'-biphenyltetracarboxylate, and sodium biphenyl-3,3',4,4',5',5'-hexacarboxylate.

[0024] Furthermore, the positive electrode active material is a polyanion positive electrode material, a Prussian blue positive electrode material or a layered oxide positive electrode material.

[0025] Furthermore, the polyanion positive electrode materials are sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7), sodium vanadium phosphate (Na3V2(PO4)3), sodium iron sulfate (Na2Fe(SO4)2), sodium manganese titanium phosphate, tunnel phase Na 0.44 MnO2, layered Na 0.67 MnO2, Na 0.67 Ni 0.33 Mn 0.67 One or more of O2.

[0026] Furthermore, the binder is one or more of tetrafluoroethylene, polytetrafluoroethylene, sodium carboxymethyl cellulose, polyacrylic acid. Furthermore, the conductive agent is one or more of super P, acetylene black, Ketjen black, and carbon nanotubes.

[0027] Furthermore, the positive electrode sheet is coated on a positive electrode current collector, and the positive electrode current collector is a copper foil or an aluminum foil.

[0028] Furthermore, in the positive electrode sheet, the weight ratio of the positive electrode active material, the conductive agent, the binder and the overcharge prevention additive is 70-90:10-20:10-20:0.01-20.

[0029] In the present invention, the test voltage range of the overcharge prevention effect is 4.5-5.0 V, firstly, to detect the supplement effect of the decomposition of the composite aromatic sodium carboxylate on the active sodium ions in the system. As the voltage is further increased, the decomposition products of the composite aromatic sodium carboxylate undergo electrochemical polymerization under high voltage to form a conductive film on the cathode surface, and the polymer deposits may develop to penetrate the isolation membrane to reach the anode surface, thereby causing an internal short circuit, causing the overcharged battery to automatically discharge to a safer charging state, which is reflected in the charge and discharge curve as a long platform under high voltage, which lasts for a period of time and then the voltage drops sharply; The anti-overcharge additive of the present invention also has a sodium supplementation effect. Specifically, the normal sodium supplementation effect test voltage range is 2-4.5 V, which is to allow the aromatic sodium carboxylate to be completely decomposed. The low decomposition voltage of the aromatic sodium carboxylate is because the introduction shows that the aromatic sodium carboxylate has a lower oxidation decomposition voltage than ordinary sodium carboxylate because of the adjustment of its molecular structure and the increase of its electron cloud density. The carboxylic acid group is more easily dissociated. These characteristics make the aromatic sodium carboxylate a more effective sodium supplementation additive, which helps to improve the energy density and performance of sodium-ion batteries; The present invention adds a multifunctional anti-overcharge additive, sodium aromatic carboxylate, to the sodium ion positive electrode material, detects its sodium supplementation effect through electrochemical testing, effectively improves the specific capacity of the sodium ion battery, and uses the characteristics of high-voltage polymerization of its decomposition product to achieve the anti-overcharge effect, providing an effective technical solution for the commercial production of high-specific energy and high-safety sodium ion batteries. Sodium supplement is an additive used in sodium ion batteries to compensate for the irreversible loss of sodium ions in the positive electrode material during the battery charging and discharging process. The existing sodium supplement is easy to cause the decomposition of the electrolyte due to its high oxidation potential, thereby affecting the stability and energy density of the battery. In addition, overcharge protection is an important factor in ensuring the safety of sodium ion batteries to ensure that it can effectively prevent thermal runaway and explosion risks when the battery is overcharged. In the prior art, there is a lack of multifunctional additives that can simultaneously have the functions of sodium supplementation and overcharge protection. At the same time, due to the adjustment of its molecular structure and the increase of electron cloud density, its carboxylic acid group is more easily dissociated, thereby having a lower oxidation decomposition voltage than ordinary sodium carboxylate. These characteristics make the aromatic sodium carboxylate also have the effect of a sodium supplement additive, which helps to improve the energy density and electrochemical performance of sodium ion batteries. It can also polymerize at high voltage, and electrochemically polymerize at overcharge potential to form a conductive film on the cathode surface. The polymer deposits may develop to penetrate the isolation membrane to reach the anode surface, resulting in an internal short circuit, causing the overcharged battery to automatically discharge to a safer charging state. In the normal charging and discharging process, the sodium ions produced by the oxidation and decomposition of the aromatic carboxylic acid sodium are used to compensate for the irreversible loss of active sodium ions caused by the formation of the SEI film at the negative electrode, and the role of the additive as an overcharge protector is tested through overcharge experiments to obtain a sodium ion battery with high specific energy and high safety.

[0030] Example 1 This embodiment relates to a sodium ion battery positive electrode sheet and a sodium ion battery using the positive electrode sheet, and the preparation steps are as follows: The positive electrode material sodium ferric phosphate pyrophosphate (NFPP) and the conductive agent (SP) and the binder PVDF were mixed in a mass ratio of 80:10:10, and then 5% of 3,3',4,4'-biphenyltetracarboxylic acid sodium and 1,4,5,8-naphthalenetetracarboxylic acid sodium (10:100) were added to further mix and slurry. After mixing, the slurry was coated on aluminum foil and placed in a vacuum oven at 100°C for 8 hours for use. A sodium ion battery was assembled with 3,3',4,4'-biphenyltetracarboxylic acid sodium and 1,4,5,8-naphthalenetetracarboxylic acid sodium (5% addition) and the positive electrode material sodium ferric phosphate pyrophosphate as the composite positive electrode, and the electrochemical test was carried out. The recorded capacity was 118.5 mAh g when charged to 4.5 V. -1 , and continue charging until the oxidative polymerization platform appears, and record the average voltage V as 4.6 V.

[0031] Example 2 This embodiment relates to a sodium ion battery positive electrode sheet and a sodium ion battery using the positive electrode sheet, and the preparation steps are as follows: The positive electrode material sodium ferric phosphate pyrophosphate (NFPP) and the conductive agent (SP) and the binder PVDF were mixed in a mass ratio of 80:10:10, and then 10% of 3,3',4,4'-biphenyltetracarboxylic acid sodium and 1,4,5,8-naphthalenetetracarboxylic acid sodium (10:100) were added to further mix and slurry. After mixing, the slurry was coated on aluminum foil and placed in a vacuum oven at 100°C for 8 hours for use. A sodium ion battery was assembled with 3,3',4,4'-biphenyltetracarboxylic acid sodium and 1,4,5,8-naphthalenetetracarboxylic acid sodium (10% addition) and the positive electrode material sodium ferric phosphate pyrophosphate as the composite positive electrode, and the electrochemical test was carried out. The recorded capacity was 132.1mAh g when charged to 4.5 V. -1 , and continue charging until the oxidative polymerization platform appears, and the average voltage V is recorded as 4.63 V.

[0032] Example 3 This embodiment relates to a sodium ion battery positive electrode sheet and a sodium ion battery using the positive electrode sheet, and the preparation steps are as follows: The positive electrode material sodium ferric phosphate pyrophosphate (NFPP) and the conductive agent (SP) and the binder PVDF were mixed in a mass ratio of 80:10:10, and then 5% of 3,3',4,4'-biphenyltetracarboxylic acid sodium and 1,4,5,8-naphthalenetetracarboxylic acid sodium (10:1) were added to further mix and slurry. After mixing, the slurry was coated on aluminum foil and placed in a vacuum oven at 100°C for 8 hours for use. A sodium ion battery was assembled with 3,3',4,4'-biphenyltetracarboxylic acid sodium and 1,4,5,8-naphthalenetetracarboxylic acid sodium (5% addition) and the positive electrode material sodium ferric phosphate pyrophosphate as the composite positive electrode, and the electrochemical test was carried out. The recorded capacity was 119.1 mAh g when charged to 4.5 V. -1, and continue charging until the oxidative polymerization platform appears, and the recorded voltage V is 4.74 V.

[0033] Example 4 This embodiment relates to a sodium ion battery positive electrode sheet and a sodium ion battery using the positive electrode sheet, and the preparation steps are as follows: The positive electrode material sodium vanadium phosphate (NVP) and the conductive agent (KB) and the binder PVDF were mixed in a mass ratio of 80:10:10, and then 5% of 3,3',4,4'-biphenyltetracarboxylic acid sodium and 1,4,5,8-naphthalenetetracarboxylic acid sodium (10:100) were added. After mixing, the slurry was coated on aluminum foil and placed in a vacuum oven at 100°C for drying. A sodium ion battery was assembled with 3,3',4,4'-biphenyltetracarboxylic acid sodium and 1,4,5,8-naphthalenetetracarboxylic acid sodium (5% addition) and the positive electrode material sodium vanadium phosphate (NVP) as the composite positive electrode, and the electrochemical test was carried out. The recorded capacity was 131.4 mAh g when charged to 4.5 V. -1 , and continue charging until the oxidative polymerization platform appears, and the recorded voltage V is 4.61 V.

[0034] Example 5 This embodiment relates to a sodium ion battery positive electrode sheet and a sodium ion battery using the positive electrode sheet, and the preparation steps are as follows: The positive electrode material sodium vanadium phosphate (NVP) and the conductive agent (KB) and the binder PVDF were mixed in a mass ratio of 70:20:10, and then 7% of biphenyl-3,3',4,4',5',5'-hexacarboxylic acid sodium and 2,3,6,7-naphthalenetetracarboxylic acid sodium (10:1) were added to further mix and slurry. After mixing, the slurry was coated on aluminum foil and placed in a vacuum oven at 100°C for drying. A sodium ion battery was assembled with biphenyl-3,3',4,4',5',5'-hexacarboxylic acid sodium and 2,3,6,7-naphthalenetetracarboxylic acid sodium (7% addition) and the positive electrode material sodium vanadium phosphate (NVP) as the composite positive electrode, and the electrochemical test was carried out. The recorded capacity was 147.2mAh g when charged to 4.5 V. -1 , continue charging until the oxidative polymerization platform appears, and record the voltage V as 4.74V.

[0035] Example 6 This embodiment relates to a sodium ion battery positive electrode sheet and a sodium ion battery using the positive electrode sheet, and the preparation steps are as follows: The positive electrode material sodium vanadium phosphate (NVP) and the conductive agent (KB) and the binder PVDF were mixed in a mass ratio of 70:20:10, and then 10% of biphenyl-3,3',4,4',5',5'-sodium hexacarboxylate and sodium 2,3,6,7-naphthalenetetracarboxylate (10:10) were added to further mix and slurry. After mixing, the slurry was coated on aluminum foil and placed in a vacuum oven at 100°C for drying. A sodium ion battery was assembled with biphenyl-3,3',4,4',5',5'-sodium hexacarboxylate and sodium 2,3,6,7-naphthalenetetracarboxylate (10% addition) and the positive electrode material sodium vanadium phosphate (NVP) as the composite positive electrode, and the electrochemical test was carried out. The recorded capacity was 146.8mAh g when charged to 4.5 V. -1 , continue charging until the oxidative polymerization platform appears, and record the voltage V as 4.65V.

[0036] Example 7 This embodiment relates to a sodium ion battery positive electrode sheet and a sodium ion battery using the positive electrode sheet, and the preparation steps are as follows: The positive electrode material Na 0.44 MnO2 (NMO) and conductive agent (AB) and binder PVDF were mixed in a mass ratio of 80:10:10, and then 20% of biphenyl-3,3',4,4',5',5'-hexacarboxylic acid sodium and 2,3,6,7-naphthalenetetracarboxylic acid sodium (10:1) were added to further mix and slurry. After mixing, the slurry was coated on aluminum foil and placed in a vacuum oven at 100°C for drying. 0.44 MnO2 (NMO) was used as the composite cathode to assemble a sodium-ion battery. The electrochemical test showed that the recorded capacity was 125.1 mAh g when charged to 4.5 V. -1 , continue charging until the oxidative polymerization platform appears, and record the voltage V as 4.72V.

[0037] Comparative Example 1 This embodiment relates to a sodium ion battery positive electrode sheet and a sodium ion battery using the positive electrode sheet, and the preparation steps are as follows: The positive electrode material sodium iron phosphate pyrophosphate (NFPP) and the conductive agent (SP) and the binder PVDF were mixed in a mass ratio of 80:10:10, and then homogenized. After mixing, the slurry was coated on aluminum foil and placed in a vacuum oven at 100°C for drying. Sodium iron phosphate pyrophosphate (NFPP) was used as the positive electrode and metallic sodium was used as the negative electrode to assemble a sodium ion battery. The electrochemical test was performed and the capacity was recorded as C of 104.5 mAh g when charged to 4.5 V. -1 , and no platform appeared when the battery was charged to 4.8V. The test results are shown in Table 1.

[0038] Comparative Example 2 This embodiment relates to a sodium ion battery positive electrode sheet and a sodium ion battery using the positive electrode sheet, and the preparation steps are as follows: The positive electrode material sodium vanadium phosphate (NVP) and the conductive agent (KB) and the binder PVDF were mixed in a mass ratio of 70:20:10, and then homogenized. After mixing, the slurry was coated on aluminum foil and placed in a vacuum oven at 100°C for drying. Sodium iron phosphate pyrophosphate (NFPP) was used as the positive electrode and metallic sodium was used as the negative electrode. The sodium ion battery was assembled and electrochemically tested. The capacity was recorded as C of 115 mAh g when charged to 4.5 V. -1 , and no platform appeared when the battery was charged to 4.8V. The test results are shown in Table 1.

[0039] Comparative Example 3 This embodiment relates to a sodium ion battery positive electrode sheet and a sodium ion battery using the positive electrode sheet, and the preparation steps are as follows: The positive electrode material is tunnel-type Na 0.44 MnO2 (NMO), conductive agent (AB) and binder PVDF were mixed in a mass ratio of 80:10:10, and then homogenized. After mixing, the slurry was coated on aluminum foil and dried in a vacuum oven at 100°C for later use. 0.44 MnO2 (NMO) was used as the positive electrode and metallic sodium was used as the negative electrode. The sodium ion battery was assembled and electrochemically tested. The capacity C was recorded as 62 mAh g when charged to 4.5 V. -1 , and no platform appeared when the battery was charged to 4.8V. The test results are shown in Table 1.

[0040] Comparative Example 4 This embodiment relates to a sodium ion battery positive electrode sheet and a sodium ion battery using the positive electrode sheet, and the preparation steps are as follows: The positive electrode material Na 0.44 MnO2 (NMO) and conductive agent (AB) and binder PVDF were mixed in a mass ratio of 80:10:10, and then 30% of biphenyl-3,3',4,4',5',5'-hexacarboxylic acid sodium and 2,3,6,7-naphthalenetetracarboxylic acid sodium (10:1) were added to further mix and slurry. After mixing, the slurry was coated on aluminum foil and placed in a vacuum oven at 100°C for drying. 0.44 MnO2 (NMO) was used as the composite positive electrode to assemble a sodium-ion battery and perform electrochemical testing. The recorded capacity was 122 mAhg when charged to 4.5 V. -1 , and continued charging to 5.0V without the appearance of an oxidative polymerization platform.

[0041] The above embodiment was subjected to performance testing, and the test results are shown in Table 1: Table 1 Performance test results From Example 1, Example 2, and Comparative Example 1, it can be seen that as the proportion of additives increases, the supplementary capacity of sodium ferric pyrophosphate also increases. Compared with Comparative Example 1, as overcharging proceeds, at a voltage of 4.6V, a platform of oxidative polymerization of the decomposition products of the aromatic sodium carboxylate appears, preventing the voltage from further increasing, thereby avoiding safety accidents. Similarly, from Example 4 and Comparative Example 2, it can be seen that the addition of 10% of the aromatic sodium carboxylate can significantly increase the charge capacity of the sodium vanadium phosphate.

[0042] It can be seen from Example 1 and Example 3 that after increasing the proportion of sodium biphenyl aromatic carboxylate, its overcharge protection voltage threshold is increased by 4.74V, and the voltage of oxidative polymerization after decomposition of sodium biphenyl aromatic carboxylate is higher.

[0043] It can be seen from Examples 5 and 6 that sodium biphenyl aromatic carboxylate can contain more sodium carboxylate substitutions. Increasing the proportion of sodium biphenyl aromatic carboxylate can achieve a higher sodium supplementation effect with a smaller addition amount, which is more conducive to improving the energy density of the battery.

[0044] From Example 7 and Comparative Example 4, it can be seen that the amount added should not be too large, otherwise the battery conductivity will be reduced, the electrochemical polarization will be increased, the capacity cannot be fully utilized, and the voltage division effect will be enhanced due to the excessive internal resistance, and the overcharge prevention effect cannot be effectively demonstrated.

[0045] Therefore, by adding complex aromatic sodium carboxylates as additives to sodium-ion batteries, by regulating sodium biphenyl aromatic carboxylates and sodium naphthyl aromatic carboxylates, effective sodium supplementation effects and controllable overcharge voltage protection thresholds were demonstrated, reflecting the versatility of complex aromatic sodium carboxylate additives.

[0046] The above embodiments are only specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. An anti-overcharge type sodium ion battery positive electrode sheet, comprising a positive electrode active material, a conductive agent and a binder, characterized in that: An anti-overcharge additive is also added, and the anti-overcharge additive is an aromatic sodium carboxylate.

2. The anti-overcharge type sodium ion battery positive electrode sheet according to claim 1, characterized in that: The sodium aromatic carboxylate is a sodium naphthyl aromatic carboxylate and a sodium biphenyl aromatic carboxylate in a molar ratio of 10:1-100.

3. The anti-overcharge type sodium ion battery positive electrode sheet according to claim 2, characterized in that: The sodium naphthyl aromatic carboxylate is sodium 1,4,5,8-naphthalenetetracarboxylate and / or sodium 2,3,6,7-naphthalenetetracarboxylate.

4. The anti-overcharge type sodium ion battery positive electrode sheet according to claim 2, characterized in that: The sodium biphenyl aromatic carboxylate is one or more of 4,4'-biphenyl dicarboxylate sodium, 3,3',4,4'-biphenyl tetramethyl sodium, 2,3,3',4'-biphenyl tetracarboxylate sodium, and biphenyl-3,3',4,4',5',5'-hexacarboxylate sodium.

5. The anti-overcharge type sodium ion battery positive electrode sheet according to claim 3 or 4, characterized in that: The positive electrode active material is a polyanion positive electrode material, a Prussian blue positive electrode material or a layered oxide positive electrode material.

6. The anti-overcharge type sodium ion battery positive electrode sheet according to claim 5, characterized in that: The polyanion positive electrode material is sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7), sodium vanadium phosphate (Na3V2(PO4)3), sodium iron sulfate (Na2Fe(SO4)2), sodium manganese titanium phosphate, tunnel phase Na 0.44 MnO2, layered Na 0.67 MnO2, Na 0.67 Ni 0.33 Mn 0.67 One or more of O2.

7. The anti-overcharge type sodium ion battery positive electrode sheet according to claim 6, characterized in that: The binder is one or more of tetrafluoroethylene, polytetrafluorovinylidene, sodium carboxymethyl cellulose and polyacrylic acid.

8. The anti-overcharge type sodium ion battery positive electrode sheet according to claim 7, characterized in that: The conductive agent is one or more of super P, acetylene black, Ketjen black and carbon nanotubes.

9. The anti-overcharge type sodium ion battery positive electrode sheet according to claim 8, characterized in that: The positive electrode sheet is coated on a positive electrode current collector, and the positive electrode current collector is a copper foil or an aluminum foil.

10. The anti-overcharge type sodium ion battery positive electrode sheet according to claim 9, characterized in that: In the positive electrode sheet, the weight ratio of the positive electrode active material, the conductive agent, the binder and the overcharge prevention additive is 70-90:10-20:10-20:0.01-20.

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