An anti-overcharge type sodium ion battery positive electrode sheet

Abstract

The present invention discloses an anti-overcharge 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 a sodium aromatic carboxylate. The anti-overcharge sodium ion battery positive electrode sheet of the present invention has good overcharge prevention, excellent electrochemical performance, and high safety.

Description

Technical Field

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

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

[0003] In sodium-ion batteries (SIBs), overcharge protection is a key safety consideration. Overcharging can lead to increased internal pressure in the battery and may even trigger thermal runaway and explosion. Therefore, developing effective overcharge protectors is crucial to improving 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 and are reduced to electrons, 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 present invention aims 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 achieved through the following technical solutions:

[0008] 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.

[0009] Furthermore, the sodium aromatic carboxylate is sodium naphthyl aromatic carboxylate and sodium biphenyl aromatic carboxylate in a molar ratio of 10:1-100.

[0010] In the present invention, the chemical formula of 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), where n is the number of sodium carboxylates substituted in the aromatic structure. If the number is less than 2, the theoretical specific capacity is too low and the sodium replenishment effect is too poor. However, due to the large steric hindrance, it is difficult to obtain more than 6 sodium carboxylates substituted in the aromatic structure.

[0011] In the aromatic sodium carboxylate of the present invention, the molar ratio of sodium naphthyl aromatic carboxylate and sodium biphenyl aromatic carboxylate is 10:1-100, including but not limited to 10:1, 10:10, 10:90, 10:100 and the like. Because from the perspective of spatial structure, biphenyl is a non-planar structure, and the number of substitutions of sodium carboxylate derivatives on the biphenyl aromatic ring is higher, a sodium biphenyl aromatic carboxylate with a higher specific capacity can be obtained. Naphthalene is a planar structure. When sodium carboxylate replaces the hydrogen on the naphthalene aromatic ring, it faces greater steric hindrance, and it is difficult to obtain sodium naphthyl aromatic carboxylate with more than four substitutions. Also due to the steric hindrance effect, the oxidative polymerization potential of naphthalene is lower. Based on these two characteristics, the ratio of the two sodium aromatic carboxylates can be adjusted according to demand. Increasing the ratio of sodium biphenyl aromatic carboxylate can obtain a higher overcharge threshold voltage, and increasing the ratio of polysubstituted sodium biphenyl aromatic carboxylate can more effectively improve energy density and efficiency.

[0012] Furthermore, the sodium naphthyl aromatic carboxylate is sodium 1,4,5,8-naphthalenetetracarboxylate and / or sodium 2,3,6,7-naphthalenetetracarboxylate. Using the planar polycyclic aromatic hydrocarbon naphthalene as a substrate, multiple sodium carboxylate functional groups are introduced onto the aromatic ring. Due to steric hindrance, the number of introduced functional groups is 2 to 4. The additive undergoes two main electrochemical reactions in the positive electrode: first, decarboxylation and desodiumation at low voltage. The released active sodium ions can compensate for the irreversible loss of sodium ions in the battery. Second, electro-oxidative polymerization occurs. As overcharging proceeds, the decarboxylation and desodiumation-depleted naphthalene undergoes electro-oxidative polymerization to form a highly resistive conductive polymer layer. This polymer layer can prevent further release and insertion of sodium ions. Simultaneously, the growing polymer layer gradually conducts electricity between the positive and negative electrodes, maintaining the voltage within a safe voltage range through self-discharge. The planar structure of naphthalene has a high electron density and a relatively stable electron cloud distribution. This electron mobility and stability may make the planar structured molecule more active during oxidative polymerization, resulting in a lower oxidative polymerization potential.

[0013] Furthermore, the sodium biphenyl aromatic carboxylate is one or more of sodium 4,4'-biphenyldicarboxylate, sodium 3,3',4,4'-biphenyltetracarboxylate, sodium 2,3,3',4'-biphenyltetracarboxylate, and sodium biphenyl-3,3',4,4',5',5'-hexacarboxylate. Using the non-planar polycyclic aromatic hydrocarbon biphenyl as the base, 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 voltage. The released active sodium ions can compensate for the irreversible loss of sodium ions in the battery. The second is electro-oxidative polymerization. As overcharging 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 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 will be kept within the safe voltage range through self-discharge. In contrast to naphthalene, the potential of biphenyl oxidative polymerization is higher in the non-planar structure of biphenyl.

[0014] Furthermore, the positive electrode active material is a polyanionic 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 cycle of charging, the additive undergoes decarboxylation and desodiumization. The decarboxylation and desodiumization products do not participate in the electrochemical reaction during normal charging and discharging.

[0015] 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 Ni0.33 Mn 0.67 One or more of O2.

[0016] Furthermore, the binder is one or more of tetrafluoroethylene, polytetrafluoroethylene, sodium carboxymethyl cellulose, polyacrylic acid,

[0017] Furthermore, the conductive agent is one or more of super P, acetylene black, Ketjen black, and carbon nanotubes.

[0018] Furthermore, the positive electrode sheet is coated on the positive electrode current collector, and the positive electrode current collector is copper foil or aluminum foil.

[0019] Furthermore, in the positive electrode sheet, the weight ratio of the positive electrode active material, conductive agent, binder, and overcharge prevention additive is 70-90:10-20:10-20:0.01-20. Specifically, the higher the amount of sodium aromatic carboxylate added, the higher the capacity it can replenish through decomposition. However, due to its relatively poor conductivity, adding too much can reduce the electrochemical performance of the battery.

[0020] The present invention provides an anti-overcharge type sodium ion battery positive electrode sheet, which has the following beneficial effects:

[0021] First, the anti-overcharge effect is good. The sodium ion battery positive electrode of the present invention is added with an anti-overcharge additive, sodium aromatic carboxylate. This additive has good air stability. Due to the adjustment of its molecular structure and the increase of its electron cloud density, its carboxylic acid group is more easily dissociated, and has a lower oxidation decomposition voltage than ordinary sodium carboxylate.

[0022] Second, the sodium-ion battery positive electrode sheet of the present invention incorporates an aromatic sodium carboxylate additive, which has a high sodium replenishment capacity and a utilization efficiency exceeding 95% due to its low decomposition voltage. The carboxyl groups on the aromatic ring can be tailored to the desired design, resulting in a sodium replenisher with a high theoretical capacity. This makes the aromatic sodium carboxylate a more effective sodium replenisher, helping to improve the energy density and performance of sodium-ion batteries. Even a 5% addition can increase the first-cycle charge capacity of a sodium-ion battery by more than 14.5 mAh / g.

[0023] Third, safety is high. The addition of an anti-overcharge additive to the sodium-ion battery cathode of the present invention significantly improves the safety of the sodium-ion battery. By adjusting the ratio of the aromatic sodium carboxylate, the overcharge threshold voltage can be widened to 4.5V-4.8V. This means that the decomposition products of the aromatic sodium carboxylate undergo electrochemical polymerization at high voltage (within the 4.5V-4.8V range), forming a conductive film on the cathode surface. The polymer deposits can then penetrate the separator and reach the anode surface, causing an internal short circuit. Simultaneously, the conductive polymer increases the battery's internal resistance, limiting the overcharge current and allowing the overcharged battery to automatically discharge to a safer state. DETAILED DESCRIPTION

[0024] 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 with reference to embodiments.

[0025] 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.

[0026] Furthermore, the sodium aromatic carboxylate is sodium naphthyl aromatic carboxylate and sodium biphenyl aromatic carboxylate in a molar ratio of 10:1-100.

[0027] Furthermore, the sodium naphthyl aromatic carboxylate is sodium 1,4,5,8-naphthalenetetracarboxylate and / or sodium 2,3,6,7-naphthalenetetracarboxylate.

[0028] Furthermore, the sodium biphenyl aromatic carboxylate is one or more of sodium 4,4'-biphenyldicarboxylate, sodium 3,3',4,4'-biphenyltetracarboxylate, sodium 2,3,3',4'-biphenyltetracarboxylate, and sodium biphenyl-3,3',4,4',5',5'-hexacarboxylate.

[0029] 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.

[0030] 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.

[0031] Furthermore, the binder is one or more of tetrafluoroethylene, polytetrafluoroethylene, sodium carboxymethyl cellulose, polyacrylic acid

[0032] Furthermore, the conductive agent is one or more of super P, acetylene black, Ketjen black, and carbon nanotubes.

[0033] Furthermore, the positive electrode sheet is coated on the positive electrode current collector, and the positive electrode current collector is copper foil or aluminum foil.

[0034] 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.

[0035] In the present invention, the test voltage range for the overcharge prevention effect is 4.5-5.0 V. First, it is to detect the effect of the decomposition of the composite aromatic sodium carboxylate on the replenishment of 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, forming a conductive film on the cathode surface. The polymer deposits may develop and 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 charge state. This is reflected in the charge-discharge curve as a long platform at high voltage, which lasts for a period of time, followed by a sudden voltage drop.

[0036] The anti-overcharge additive of the present invention also has a sodium replenishment effect. Specifically, the normal sodium replenishment effect test voltage range is 2-4.5 V, which is to allow the aromatic sodium carboxylate to completely decompose. The low decomposition voltage of the aromatic sodium carboxylate is because the introduction of the aromatic sodium carboxylate shows that due to the adjustment of its molecular structure and the increase of its electron cloud density, its carboxylic acid group is more easily dissociated, thus having a lower oxidative decomposition voltage than ordinary sodium carboxylate. These characteristics make the aromatic sodium carboxylate a more effective sodium replenishment additive, which helps to improve the energy density and performance of sodium-ion batteries;

[0037] This invention adds a multifunctional overcharge prevention additive, sodium aromatic carboxylate, to sodium-ion positive electrode materials. Electrochemical testing demonstrates its sodium replenishment effect, effectively improving the specific capacity of sodium-ion batteries. The overcharge prevention effect is achieved by leveraging the high-voltage polymerization of its decomposition products, providing an effective technical solution for the commercial production of high-energy and high-safety sodium-ion batteries. A sodium replenisher 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's charge and discharge processes. Existing sodium replenishers, due to their high oxidation potential, can easily cause electrolyte decomposition, thereby affecting battery stability and energy density. Overcharge protection is also a crucial factor in ensuring the safety of sodium-ion batteries, effectively preventing thermal runaway and explosion risks in the event of overcharge. The prior art lacks multifunctional additives that simultaneously perform sodium replenishment and overcharge protection functions. Furthermore, due to the modified molecular structure and increased electron cloud density, the carboxylic acid group dissociates more easily, resulting in a lower oxidative decomposition voltage than conventional sodium carboxylates. These properties make the aromatic sodium carboxylate a sodium replenisher, helping to improve the energy density and electrochemical performance of sodium-ion batteries. It can also polymerize at high voltages, and electrochemical polymerization occurs at overcharge potentials, forming a conductive film on the cathode surface. The polymer deposits may develop and penetrate the separator to reach the anode surface, causing an internal short circuit and causing the overcharged battery to automatically discharge to a safer charge state. During normal charge and discharge, the sodium ions produced by the oxidative decomposition of the aromatic sodium carboxylate are used to compensate for the irreversible loss of active sodium ions caused by the formation of the SEI film at the negative electrode. Overcharge experiments are also used to test the role of this additive as an overcharge protector, thereby obtaining a sodium-ion battery with high specific energy and high safety. Example

[0038] 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:

[0039] The cathode material, sodium ferric phosphate pyrophosphate (NFPP), a conductive agent (SP), and a binder, PVDF, were mixed in a mass ratio of 80:10:10. 5% sodium 3,3',4,4'-biphenyltetracarboxylate and sodium 1,4,5,8-naphthalenetetracarboxylate (10:100) were then added to further mix and slurry. After mixing, the slurry was coated on aluminum foil and dried in a vacuum oven at 100°C for 8 hours. A sodium ion battery was assembled using sodium ferric phosphate pyrophosphate (5%) as a composite cathode. Electrochemical testing revealed a recorded capacity of 118.5 mAh g when charged to 4.5 V. -1 , continue charging until the oxidative polymerization platform appears, and record the average voltage V as 4.6 V. Example

[0040] 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:

[0041] The cathode material, sodium ferric phosphate pyrophosphate (NFPP), a conductive agent (SP), and a binder, PVDF, were mixed in a mass ratio of 80:10:10. 10% sodium 3,3',4,4'-biphenyltetracarboxylate and sodium 1,4,5,8-naphthalenetetracarboxylate (10:100) were then added and further mixed to form a slurry. After mixing, the slurry was coated on aluminum foil and dried in a vacuum oven at 100°C for 8 hours. A sodium ion battery was assembled using sodium ferric phosphate pyrophosphate (NFPP) as a composite cathode, and electrochemical testing was performed. A capacity of 132.1 mAh g was recorded when charged to 4.5 V. -1 , continue charging until the oxidative polymerization platform appears, and record the average voltage V as 4.63 V. Example

[0042] 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:

[0043] The cathode material, sodium ferric phosphate pyrophosphate (NFPP), a conductive agent (SP), and a binder, PVDF, were mixed in a mass ratio of 80:10:10. 5% sodium 3,3',4,4'-biphenyltetracarboxylate and sodium 1,4,5,8-naphthalenetetracarboxylate (10:1) were then added to further mix and slurry. After mixing, the slurry was coated on aluminum foil and dried in a vacuum oven at 100°C for 8 hours. A sodium ion battery was assembled using sodium ferric phosphate pyrophosphate (5%) as a composite cathode and electrochemical testing revealed a recorded capacity of 119.1 mAh g when charged to 4.5 V. -1 , continue charging until the oxidative polymerization platform appears, and record the voltage V as 4.74 V. Example

[0044] 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:

[0045] The cathode material sodium vanadium phosphate (NVP), a conductive agent (KB), and a binder PVDF were mixed in a mass ratio of 80:10:10. Then, 5% of sodium 3,3',4,4'-biphenyltetracarboxylate and sodium 1,4,5,8-naphthalenetetracarboxylate (10:100) were added. After mixing, the slurry was coated on aluminum foil and dried in a vacuum oven at 100°C. A sodium ion battery was assembled using sodium vanadium phosphate (NVP) as the composite cathode, using sodium 3,3',4,4'-biphenyltetracarboxylate and sodium 1,4,5,8-naphthalenetetracarboxylate (5% addition) as the cathode material. Electrochemical testing showed a recorded capacity of 131.4 mAh g when charged to 4.5 V. -1 , continue charging until the oxidative polymerization platform appears, and record the voltage V as 4.61 V. Example

[0046] 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:

[0047] The cathode material sodium vanadium phosphate (NVP), a conductive agent (KB), and a binder PVDF were mixed in a mass ratio of 70:20:10. 7% sodium biphenyl-3,3',4,4',5',5'-hexacarboxylate and sodium 2,3,6,7-naphthalenetetracarboxylate (10:1) were then added to further mix and slurry. After mixing, the slurry was coated on aluminum foil and dried in a vacuum oven at 100°C. A sodium ion battery was assembled using sodium biphenyl-3,3',4,4',5',5'-hexacarboxylate and sodium 2,3,6,7-naphthalenetetracarboxylate (7% addition) as the composite cathode material sodium vanadium phosphate (NVP). Electrochemical testing was performed, and a recorded capacity of 147.2 mAh g was obtained when charged to 4.5 V. -1 , continue charging until the oxidative polymerization platform appears, and record the voltage V as 4.74V. Example

[0048] 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:

[0049] The cathode material sodium vanadium phosphate (NVP) was mixed with a conductive agent (KB) and a binder PVDF in a mass ratio of 70:20:10. 10% sodium biphenyl-3,3',4,4',5',5'-hexacarboxylate and sodium 2,3,6,7-naphthalenetetracarboxylate (10:10) were then added to further mix and slurry. After mixing, the slurry was coated on aluminum foil and dried in a vacuum oven at 100°C. A sodium ion battery was assembled using sodium biphenyl-3,3',4,4',5',5'-hexacarboxylate and sodium 2,3,6,7-naphthalenetetracarboxylate (10% addition) as the composite cathode material and sodium vanadium phosphate (NVP). Electrochemical testing was performed, and a capacity of 146.8 mAh g was recorded when charged to 4.5 V.-1 , continue charging until the oxidative polymerization platform appears, and record the voltage V as 4.65V. Example

[0050] 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:

[0051] 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 homogenize. 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. Electrochemical tests were performed and 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.

[0052] 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:

[0053] The positive electrode material, sodium ferric pyrophosphate (NFPP), 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 dried in a vacuum oven at 100°C. A sodium ion battery was assembled using sodium ferric pyrophosphate (NFPP) as the positive electrode and metallic sodium as the negative electrode. Electrochemical testing was performed, and the capacity (C) was recorded as 104.5 mAh g when charged to 4.5 V. -1 , and continued to charge to 4.8V without any platform appearing. The test results are shown in Table 1.

[0054] 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:

[0055] The cathode material sodium vanadium phosphate (NVP), 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 dried in a vacuum oven at 100°C. A sodium ion battery was assembled using sodium ferric pyrophosphate (NFPP) as the positive electrode and metallic sodium as the negative electrode. Electrochemical testing was performed, and the capacity (C) was recorded as 115 mAh g when charged to 4.5 V. -1, and continued to charge to 4.8V without any platform appearing. The test results are shown in Table 1.

[0056] 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:

[0057] The cathode material 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. 0.44 MnO2 (NMO) was used as the positive electrode and metallic sodium was used as the negative electrode. A 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 continued to charge to 4.8V without any platform appearing. The test results are shown in Table 1.

[0058] 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:

[0059] 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 homogenize. 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, and electrochemical testing was performed. The recorded capacity was 122 mAhg when charged to 4.5 V. -1 , continue charging to 5.0V and no oxidation polymerization platform appears.

[0060] The above embodiment was subjected to performance testing, and the test results are shown in Table 1:

[0061] Table 1 Performance test results

[0062]

[0063] As can be seen from Examples 1 and 2, as well as Comparative Example 1, the capacity of sodium ferric pyrophosphate supplemented with the additive increases with increasing proportions. Compared to Comparative Example 1, as overcharge progresses, a platform of oxidative polymerization of the aromatic sodium carboxylate decomposition products appears at 4.6V, preventing further voltage increases and thus avoiding safety incidents. Similarly, as can be seen from Example 4 and Comparative Example 2, a 10% addition of the aromatic sodium carboxylate significantly increases the specific charge capacity of the sodium vanadium phosphate.

[0064] It can be seen from Example 3 that after increasing the proportion of sodium biphenyl aromatic carboxylate, the overcharge protection voltage threshold is increased by 4.74V, and the voltage of oxidative polymerization after decomposition of sodium biphenyl aromatic carboxylate is even higher.

[0065] 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.

[0066] From Example 7 and Comparative Example 4, it can be seen that the added amount 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 drop effect will be enhanced due to excessive internal resistance, and the overcharge prevention effect cannot be effectively demonstrated.

[0067] Therefore, by adding complex aromatic sodium carboxylates as additives to sodium ion batteries, and by regulating sodium biphenyl aromatic carboxylates and sodium naphthyl aromatic carboxylates, effective sodium replenishment effects and controllable overcharge voltage protection thresholds were demonstrated, reflecting the versatility of complex aromatic sodium carboxylate additives.

[0068] The above embodiments are merely specific embodiments of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the scope of the present invention, and such obvious alternatives are all within the scope of protection 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; The sodium aromatic carboxylate is sodium naphthyl aromatic carboxylate and sodium biphenyl aromatic carboxylate in a molar ratio of 10:1-100; the sodium naphthyl aromatic carboxylate is sodium 1,4,5,8-naphthalenetetracarboxylate and / or sodium 2,3,6,7-naphthalenetetracarboxylate; the sodium biphenyl aromatic carboxylate is one or more of sodium 4,4'-biphenyldicarboxylate, sodium 3,3',4,4'-biphenyltetracarboxylate, sodium 2,3,3',4'-biphenyltetracarboxylate, and sodium biphenyl-3,3',4,4',5',5'-hexacarboxylate; 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.

2. The anti-overcharge sodium ion battery positive electrode according to claim 1, 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.

3. The anti-overcharge sodium ion battery positive electrode according to claim 2, characterized in that: The polyanion positive electrode material is sodium iron pyrophosphate, sodium vanadium phosphate, sodium iron sulfate, 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.

4. The anti-overcharge sodium ion battery positive electrode according to claim 3, characterized in that: The binder is one or more of tetrafluoroethylene, polytetrafluoroethylene, sodium carboxymethyl cellulose and polyacrylic acid.

5. The overcharge-proof sodium ion battery positive electrode sheet according to claim 4, wherein: The conductive agent is one or more of super P, acetylene black, Ketjen black, and carbon nanotubes.

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