Preparation method of positive electrode of high-temperature-resistant lithium primary battery

Abstract

The invention provides a preparation method of a positive electrode of a high-temperature-resistant lithium primary battery, which comprises the following steps: uniformly mixing a positive electrode active material, a positive electrode additive, a conductive agent and an adhesive, and preparing a positive electrode plate by a lithium primary battery positive electrode processing technology; the positive electrode active material comprises sintered manganese dioxide; the positive electrode additive is a boron-containing magnesium compound; the mass ratio of the positive electrode active material to the boron-containing magnesium compound is 1: (0.005-0.1). According to the invention, the boron-containing magnesium compound is directly introduced into the positive electrode of the lithium primary battery as a source of boron element and magnesium element, so that a mixing step does not need to be additionally added before sintering, the preparation process is reduced, and the labor and equipment cost is reduced; in addition, after the produced battery is stored at 125 DEG C for 100 hours, the CCV of the battery and the expansion of the battery are smaller.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more particularly to a method for preparing the positive electrode of a high-temperature resistant lithium primary battery. Background Technology

[0002] With the continuous depletion of fossil fuels and their non-renewable nature, the resulting energy crisis and environmental problems are becoming increasingly prominent. Therefore, developing efficient and stable energy conversion and storage devices has become a research hotspot. Among these, lithium primary batteries, with their high energy density, are widely used in military, intelligent transportation, smart meters, and biomedical fields. As application scenarios expand, the requirements for battery discharge performance under extreme conditions and storage stability are also gradually increasing.

[0003] When subjected to high-temperature discharge and storage conditions, lithium primary batteries using manganese dioxide as the positive electrode often encounter problems such as battery gas generation leading to battery expansion, poor internal contact, and increased internal resistance.

[0004] CN 112470307A describes a method for improving lithium / manganese dioxide primary batteries by adding a boron-containing compound (the boron compound includes at least one selected from H3BO3, B2O3, HBO2, H4B2O4, Li3BO3, LiBO2, and Li4B2O4) to the positive electrode. However, while boron doping can prevent gas generation at high temperatures, it also increases the polarization of the battery.

[0005] CN 101978533B describes a method for preparing low-crystallinity manganese dioxide by mixing boron-containing compounds (boron oxide, boric acid, metaboric acid, etc.) with compounds containing Group II elements of the periodic table (oxides, hydroxides, carbonates, etc.) and manganese dioxide, followed by high-temperature sintering. This manganese dioxide can be used as a positive electrode active material for lithium batteries. While this method addresses the issue of gas generation in lithium batteries at high temperatures to some extent, it requires mixing materials during the sintering step, increasing the number of steps. Furthermore, the degree of dispersion between the boron-containing compounds and the Group II compounds can affect battery performance.

[0006] Therefore, it is very important to study a cathode preparation method that is suitable for lithium primary batteries with manganese dioxide as the cathode, can suppress the problem of gas expansion at high temperature, is convenient and simple without increasing the production process, and has uniform material distribution. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing the positive electrode of a high-temperature resistant lithium primary battery.

[0008] The technical solution to achieve the purpose of this invention is: a method for preparing a positive electrode for a high-temperature resistant lithium primary battery, which involves uniformly mixing positive electrode active material, positive electrode additive, conductive agent and binder, and then preparing a positive electrode sheet through a lithium primary battery positive electrode processing technology. The positive electrode active material comprises sintered manganese dioxide; The positive electrode additive is a boron-magnesium compound; The mass ratio of the positive electrode active material to the boron-magnesium compound is 1:(0.005~0.1).

[0009] The positive electrode active material, conductive agent, and binder described in this invention all use conventional formulations for primary lithium batteries. The processing technology for the positive electrode of a primary lithium battery is a conventional process, namely: first, roll-forming the positive electrode powder into positive electrode powder, and then pressing the positive electrode powder into positive electrode sheets.

[0010] Boron, being an electron-deficient element, possesses the ability to coordinate with transition metals. Manganese in manganese dioxide is also a transition metal, and boron coordination can effectively reduce the dissolution of manganese ions into the battery electrolyte at high temperatures. However, excessive boron content can increase battery polarization. By introducing low-electron-negativity magnesium ions into the cathode material, the Mn3d-O2p orbital hybridization is enhanced, thereby optimizing the electronic structure. Magnesium ions primarily contribute s and p orbitals to the Mg-O bond; the bond energies formed by these orbitals are significantly lower than the interaction energy between 3d and 2p orbitals, thus enhancing orbital interactions and lattice stability. Magnesium doping increases the tendency for electrons to migrate towards bridging oxygen atoms (Mn-O-Mg). This asymmetric electron distribution is beneficial for reducing the band gap and improving diffusion kinetics, thereby reducing the polarization caused by boron doping. Therefore, this invention introduces boron and magnesium elements into the manganese dioxide-containing cathode of a lithium primary battery to address the problems of gas expansion and polarization in lithium primary batteries at high temperatures.

[0011] Given that adding boron and magnesium separately makes it easier to optimize their respective amounts, which is beneficial for maximizing the balance between high-temperature stability (suppressing gas) and electrochemical performance (capacity, voltage), battery engineers typically choose to add boron and magnesium compounds separately to manganese dioxide. However, this invention breaks with convention by directly introducing boron-magnesium compounds as the source of boron and magnesium elements during the mixing process of the positive electrode active material with the conductive agent and binder. This not only eliminates the need for an additional mixing step before sintering, reducing the preparation process and lowering labor and equipment costs, but also, according to tests, the present invention, when incorporating boron-magnesium compounds into the positive electrode raw material, results in a smaller CCV and smaller battery expansion after storage at 125°C for 100 hours compared to incorporating boron and magnesium compounds separately. The reason for this is speculated to be that since the boron-magnesium compounds contain both boron and magnesium elements, the two elements are already atomically mixed in the compound. This atomically uniform mixing of boron and magnesium elements is more conducive to suppressing gas generation at high temperatures and maintaining the uniformity of material performance.

[0012] Furthermore, the boron-containing magnesium compound is any one or a combination of two or more of magnesium boride (MgB2), magnesium metaborate (MgBO2), and magnesium borate (Mg3(BO3)2). Detailed Implementation

[0013] The preferred embodiment of the method for preparing the positive electrode of the high-temperature resistant lithium primary battery of the present invention will now be described in detail. Example 1

[0014] A method for preparing the positive electrode of a high-temperature resistant lithium primary battery involves uniformly mixing positive electrode active material, positive electrode additive, conductive agent and binder, and then preparing the positive electrode sheet using conventional lithium primary battery positive electrode processing technology (i.e., first roll pressing and granulation into positive electrode powder, and then pressing the positive electrode powder into positive electrode sheet). The positive electrode active material is sintered manganese dioxide; The positive electrode additive is a boron-magnesium compound (specifically: magnesium metaborate). The mass ratio of the positive electrode active material to the boron-magnesium compound is 1:0.03.

[0015] In Example 1, a boron-magnesium compound was added to the positive electrode of the high-temperature resistant lithium primary battery. Boron and magnesium can replace some of the manganese and react with the battery electrolyte, thereby reducing gas production and effectively suppressing battery expansion.

[0016] Following the conventional assembly process for lithium manganese primary batteries, a lithium manganese primary battery was assembled using the positive electrode sheet obtained in Example 1.

[0017] In the lithium primary battery cathode preparation methods of Examples 2-8 and Comparative Examples 1-4 of the present invention, the mass ratio of cathode additives and cathode active materials to cathode additives is shown in Table 1. Furthermore, the types and amounts of conductive agents and binders in each example and comparative example are the same as in Example 1.

[0018] Comparative Example 1 The difference between the positive electrode preparation method of Comparative Example 1 and Example 1 is only that: no boron-magnesium compound is added, that is, only the positive electrode active material, conductive agent and binder are mixed evenly to form the positive electrode sheet. Furthermore, the amount of sintered manganese dioxide added in Comparative Example 1 is the sum of the amounts of sintered manganese dioxide and boron-magnesium compound added in Example 1.

[0019] Comparative Example 2 The difference between the positive electrode preparation method of Comparative Example 2 and Example 1 lies only in that the positive electrode additive consists of two substances: boron oxide and magnesium hydroxide. Specifically, the positive electrode sheet is prepared by uniformly mixing the positive electrode active material, boron oxide, magnesium hydroxide, conductive agent, and binder, wherein the mass ratio of the positive electrode active material, boron oxide, and magnesium hydroxide is 1:0.015:0.015. The sum of the amounts of positive electrode active material, boron oxide, and magnesium hydroxide added in Comparative Example 2 is equal to the sum of the amounts of sintered manganese dioxide and boron-magnesium compounds added in Example 1.

[0020] Table 2 shows the changes in discharge capacity, CCV, and diameter of the batteries prepared in the various embodiments and comparative examples of the present invention before and after high-temperature storage (125°C for 100 hours) under 1k ohm constant resistance discharge conditions.

[0021] Table 1

[0022] Table 2

[0023] As can be seen from Comparative Examples 3, 1-6, and 4, using the same positive electrode additive (magnesium metaborate), the high-temperature discharge performance of the battery continuously improves with the increase of the amount of positive electrode additive added. However, the increase in the amount of positive electrode additive reaches an inflection point when the ratio of sintered manganese dioxide to magnesium metaborate is 1:0.1. Further increasing the amount of positive electrode additive to achieve a sintered manganese dioxide:magnesium metaborate ratio of 1:0.1 results in a significant decrease in the discharge capacity under high-temperature conditions. Furthermore, as can be seen from Comparative Example 3, when the amount of positive electrode additive added is too small, the improvement in the high-temperature resistance of the battery is not significant. Therefore, in this invention, the mass ratio of the positive electrode active material to the boron-magnesium compound is controlled at 1:(0.005-0.1).

[0024] The discharge capacity of the batteries in Examples 1-6 before high-temperature storage is less than that of Comparative Example 1 because of the reduction in the active material manganese dioxide.

[0025] The CCV of the batteries in Examples 1-6 before high-temperature storage was 3.0446V, which was lower than that of Comparative Example 1. This was because the boron-magnesium compound in the positive electrode additive reduced the valence state of manganese. After 100 hours of storage at 125°C, the batteries in Examples 1-6 still maintained a high CCV (above 2.5V) and minimal battery expansion (less than 0.08mm). In contrast, Comparative Example 1, due to its inability to suppress gas generation at high temperatures, experienced severe battery expansion, leading to poor internal contact, increased internal resistance, and a significant decrease in CCV after high-temperature storage (from 3.1403V to 1.0537V). Furthermore, after storage at 125°C, the discharge performance (above 213mAh) of the batteries in Examples 1-6 under 1kΩ constant resistance discharge conditions far exceeded that of Comparative Example 1 (0.00032mAh).

[0026] Comparing Example 4 and Comparative Example 2, it can be seen that the addition ratio of the positive electrode additive in Example 4 and Comparative Example 2 is the same, and the discharge capacity and CCV of the batteries before high-temperature storage are not significantly different. However, after storage at 125°C for 100 hours, the CCV, discharge capacity, and battery diameter change of the battery in Example 4 are significantly better than those in Comparative Example 2. This indicates that the atomic-level uniform mixing of boron and magnesium elements in boron-magnesium compounds (such as magnesium metaborate) is more conducive to suppressing gas generation in the battery at high temperatures and improving battery performance.

[0027] The positive electrode active material, conductive agent, and binder described in this invention are all conventional formulations used in primary lithium batteries.

[0028] The adhesive described in this invention can be any one or a combination of two or more of the following fluorinated resins: polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene fluoride copolymer, polyacrylic acid, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, PVDF-hexafluoropropylene copolymer, PVDF-trifluorochloroethylene copolymer, ethylene-tetrafluoroethylene copolymer, PVDF-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-trifluorochloroethylene copolymer, PVDF-hexafluoropropylene-tetrafluoroethylene copolymer, styrene-butadiene rubber, modified acrylonitrile rubber, and ethylene-acrylic acid copolymer. All of these adhesives are commonly used in lithium primary batteries.

[0029] The conductive agent described in this invention can be any one or a combination of two or more of graphite, Ketjen black, acetylene black, carbon nanotubes, graphene, BP2000, and activated carbon. These conductive agents are commonly used in lithium primary batteries.

[0030] Furthermore, in the positive electrode of a primary lithium battery, based on the total mass of the positive electrode raw materials as 100%, the amount of conductive agent and binder is usually controlled between 0.03 and 0.4%, respectively.

[0031] It should be noted that the boron-containing magnesium compound of the present invention may be, but is not limited to, magnesium boride (MgB2), magnesium metaborate (MgBO2), magnesium borate (Mg3(BO3)2), or other compounds that contain both boron and magnesium.

[0032] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent process transformations made using the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a positive electrode for a high-temperature resistant lithium primary battery, comprising uniformly mixing a positive electrode active material, a positive electrode additive, a conductive agent, and a binder, and then preparing a positive electrode sheet using a lithium primary battery positive electrode processing technology; wherein the positive electrode active material comprises sintered manganese dioxide; characterized in that: The positive electrode additive is a boron-magnesium compound; The mass ratio of the positive electrode active material to the boron-magnesium compound is 1:(0.005~0.1).

2. The method for preparing the positive electrode of a high-temperature resistant lithium primary battery according to claim 1, characterized in that: The boron-containing magnesium compound is any one or a combination of two or more of magnesium boride, magnesium metaborate, and magnesium borate.

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