A method for optimizing sodium ion positive electrode material neutralization additive and addition amount

Abstract

The invention belongs to the technical field of sodium ion batteries, and discloses a method for optimizing a neutralizing additive and an addition amount of a sodium ion positive electrode material. The optimization method comprises the following steps: assembling a plurality of groups of sodium ion batteries with different types of neutralizing acids; forming each group of sodium ion batteries using a high-precision battery testing system; performing an AC impedance test using an electrochemical workstation; and obtaining gram capacity and first discharge efficiency of each group at different charge-off data by using the formation data. The maximum value and the minimum value of the charge-off data of each group are removed, abnormal data are removed, and the rest are averaged. The Na+ diffusion coefficient is calculated by impedance fitting data, and the ohmic internal resistance and the charge transfer internal resistance are obtained. The invention can quickly determine the selection and addition amount of a neutralizing additive for sodium ion battery positive electrode materials produced by different manufacturers, thereby improving the slurry processing performance and ensuring the electrochemical performance at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a method for optimizing a sodium ion positive electrode material neutralization additive and an additive amount. Background Art

[0002] Since most of the layered cathode materials of sodium ion batteries are sintered by high-temperature solid-phase method, after sodium salt and metal oxide form layered structure by breaking and recombining chemical bonds, part of sodium salt does not enter the bulk structure of the material, but remains on the surface of the material to form alkaline substances, affecting material processing and battery performance. Too high alkalinity affects the slurry processing performance and battery performance. The current method will add some weak acid to neutralize, reduce the alkalinity of the material, and improve the processing performance and electrochemical performance. However, the amount of addition needs to be determined by DOE full electrical testing, which is relatively complicated and time-consuming. Summary of the invention

[0003] The object of the present invention is to provide a method for optimizing a neutralizing additive and an addition amount of a sodium ion positive electrode material, quickly determine the addition amount of the neutralizing additive, improve the slurry processing performance while ensuring the electrochemical performance.

[0004] To achieve the above object, the present invention provides the following technical solution: a method for optimizing the neutralization additive and the addition amount of the sodium ion positive electrode material, the optimization method comprising:

[0005] Step 1: assembling multiple groups of sodium ion batteries with different types of neutralizing acids, each group of sodium ion batteries including multiple batteries with different contents of neutralizing acids;

[0006] Step 2: Use a high-precision battery testing system to form each set of sodium-ion batteries;

[0007] Step 3: Use an electrochemical workstation to perform AC impedance testing;

[0008] Step 4: The formation data can be used to obtain the gram capacity and first discharge efficiency of each group at different charge-off times. For each group's charge-off data, the maximum and minimum values ​​are removed, as well as abnormal data, and the remaining data are averaged. The Na+ diffusion coefficient is calculated through impedance fitting data, and the ohmic internal resistance and charge transfer internal resistance are obtained. For each group's charge-off data, the maximum and minimum values ​​are removed, and the type and content of the neutralizing acid are determined based on the data obtained.

[0009] Furthermore, the first step includes

[0010] Ingredients: The positive electrode uses sodium positive electrode material, the binder uses PVDF, the conductive agent uses a composite conductive agent system of one or more of CNT, Super-p, and graphene, and different weak acids and additives with different addition amounts are selected to prepare slurries in a micro vacuum mixer. The proportion of the main components of the slurry is controlled to be consistent with the solid content, and the negative electrode uses the same metal sodium sheet;

[0011] Coating: Use a micro-coater to coat the positive electrode on the aluminum foil in a 10% humidity environment, keeping the surface density consistent;

[0012] Roller: After drying, the pole pieces of different groups of batteries are rolled to the same process thickness through rollers. The pole piece thickness is 120-121μm in a 10% humidity environment.

[0013] Slitting: Use a small cutting machine to cut into pieces in groups, with a diameter of 12mm. Take 10 small discs of equal or similar mass in each group, and carry out in a 10% humidity environment;

[0014] Assembly: The battery was assembled in an argon atmosphere glove box. Ten batteries were assembled in each group and allowed to stand for 1 hour after packaging.

[0015] Furthermore, the second step is to charge at a constant current of 0.1C to 4.0V, charge at a constant voltage to a cut-off current of 0.01C; discharge at a constant current of 0.1C to 2.0V; and charge to 55% SOC after two cycles.

[0016] Furthermore, the third step is as follows: the initial voltage is 3.65-3.68V, the scanning frequency is 100000-0.01 Hz, and the current range is 100mA.

[0017] Compared with the prior art, the present invention provides a method and application for selecting a neutralizing additive and an addition amount for a sodium ion positive electrode material, and has the following beneficial effects: the present invention can quickly determine the selection and addition amount of a neutralizing additive for sodium ion battery positive electrode materials produced by different manufacturers, thereby improving the slurry processing performance while ensuring the electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the principle of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Please refer to the attached Figure 1 The present invention uses button cell assembly and tests its gram capacity and first discharge efficiency as well as AC impedance test to find out the relationship between these data and the amount of neutralizing additive added to determine the optimal method for adding the amount of neutralizing additive. First, select the same type of neutralizing additive, add different proportions of additives and mix them into the sodium ion battery positive electrode material slurry to prepare the slurry in a micro vacuum agitator, so as to prevent denaturation during the preparation of the battery; control the proportion to be consistent with the solid content, the surface density of the pole piece, and the compaction density to ensure the consistency of the pole piece and facilitate comparison; then assemble the button cell, and the coating roller pressing and assembly process are completed in an environment with a humidity of 10%, and each scheme ensures that the operation time is consistent, which is also to reflect the influence of moisture on the material system and the effect of the acid neutralizer; the assembled battery is charged to a half-electric state after two cycles of 0.1C, and then the AC impedance test is performed, and the test parameters are kept consistent, so as to make the obtained data comparable; collect multiple groups of data (different addition amounts, the same addition amount but different types of neutralizing additives) to form a corresponding trend relationship, so that the selection and addition amount of the additive can be optimized.

[0021] The positive electrode material used for testing in the present invention is a layered oxide O3 type of positive electrode material for sodium ion batteries.

[0022] Ingredients: The positive electrode can use sodium positive electrode materials (mainly O3, P2 structure type layered oxides and other high pH sodium ion positive electrode materials), the binder uses PVDF, the conductive agent uses CNT (carbon nanotubes), Super-p, graphene or one or more composite conductive agent systems, select different weak acids (citric acid, oxalic acid, boric acid, etc.) and different addition amounts (0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%) of positive electrode materials, and prepare slurries in a micro vacuum mixer to prevent denaturation during the preparation of the battery; control the slurry ratio and solid content. The negative electrode uses metal sodium sheets.

[0023] Coating: Use a micro-coater to coat the positive electrode on aluminum foil in a 10% humidity environment.

[0024] Maintain consistent surface density

[0025] Roller rolling: After drying, the pole pieces of different groups of batteries are rolled to the same process thickness through roller rolling. The pole piece thickness is 120-121μm in a 10% humidity environment.

[0026] Slitting: Use a small cutting machine to cut into pieces in groups, with a diameter of 12mm. Take 10 small discs of equal or similar mass and size from each group. Carry out in a 10% humidity environment.

[0027] Assembly: The battery was assembled in an argon atmosphere glove box. Ten batteries were assembled in each group and allowed to stand for 1 hour after packaging.

[0028] Formation: The battery was formed using a high-precision battery testing system in the following steps: 0.1C constant current charging to 4.0V, constant voltage charging to a cut-off current of 0.01C; 0.1C constant current discharge to 2.0V; and charging to 55% SOC after two cycles.

[0029] Test: The AC impedance test was performed using an electrochemical workstation with an initial voltage of 3.65-3.68 V, a scanning frequency of 100000-0.01 Hz, and a current range of 100 mA.

[0030] Data processing: The formation data can be used to obtain the gram capacity and first discharge efficiency of each group at different charge withdrawal times. For each group's charge withdrawal data, the maximum and minimum values ​​are removed, abnormal data are removed, and the rest are averaged. The Na+ diffusion coefficient is calculated through impedance fitting data, and the ohmic internal resistance and charge transfer internal resistance are obtained. For each group's charge withdrawal data, the maximum and minimum values ​​are removed, abnormal data with large dispersion are removed, and the rest are averaged.

[0031] The test results are shown in the table. From the data in the table, it can be seen that the addition effect of oxalic acid is obviously better than that of boric acid. The gram capacity and first discharge efficiency of the material generally show a trend of change with different addition amounts; and the Na+ diffusion coefficient generally changes gradually with the change of the addition amount of oxalic acid. When the addition amount of oxalic acid is 0.1% to 0.3%, the diffusion coefficient increases; at this time, the ohmic internal resistance and charge transfer internal resistance are generally reduced, and the capacity and first efficiency also increase accordingly; but when the addition amount exceeds 0.3%, the ohmic internal resistance and charge transfer internal resistance increase instead, which may be due to the byproducts generated by the neutralization reaction of the acid that hinder the sodium ion transmission channel. According to the data, it can be preliminarily judged that the acid neutralization additive and addition amount suitable for this material can make the battery performance reach the optimal level.

[0032]

[0033] Table 1

[0034] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0035] In the description of the present invention, unless otherwise specified, "plurality" means two or more than two; the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0036] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

Claims

1. A method for optimizing the neutralization additive and the amount of the sodium ion positive electrode material, characterized in that: The preferred method includes Step 1: assembling multiple groups of sodium ion batteries with different types of neutralizing acids, each group of sodium ion batteries including multiple batteries with different contents of neutralizing acids; Step 2: Use a high-precision battery testing system to form each set of sodium-ion batteries; Step 3: Use an electrochemical workstation to perform AC impedance testing; Step 4: The formation data can obtain the gram capacity and first discharge efficiency of each group at different charge-off times. The maximum and minimum values ​​of the charge-off data of each group are removed, and the abnormal data are removed, and the rest are averaged; the Na+ diffusion coefficient is calculated through the impedance fitting data, and the ohmic internal resistance and charge transfer internal resistance are obtained. The maximum and minimum values ​​of the charge-off data of each group are removed, and the type and content of the neutralizing acid are determined by the obtained data. The third step is that the initial voltage is 3.65-3.68V, the scanning frequency is 100000-0.01 Hz, and the current range is 100mA; the second step is 0.1C constant current charging to 4.0V, constant voltage charging to a cut-off current of 0.01C; 0.1C constant current discharge to 2.0V; charge to 55% SOC after two cycles.

2. A method for neutralizing an additive and adding an additive using a preferred sodium ion positive electrode material as claimed in claim 1, characterized in that: The first step comprises Ingredients: The positive electrode uses sodium positive electrode material, the binder uses PVDF, the conductive agent uses a composite conductive agent system of one or more of CNT, Super-p, and graphene, and different weak acids and additives with different addition amounts are selected to prepare slurries in a micro vacuum mixer. The proportion of the main components of the slurry is controlled to be consistent with the solid content, and the negative electrode uses the same metal sodium sheet; Coating: Use a micro-coater to coat the positive electrode on the aluminum foil in a 10% humidity environment, keeping the surface density consistent; Roller: After drying, the pole pieces of different groups of batteries are rolled to the same process thickness through rollers. The pole piece thickness is 120-121μm in a 10% humidity environment. Slitting: Use a small cutting machine to cut into pieces in groups, with a diameter of 12mm. Take 10 small discs of equal or similar mass in each group, and carry out in a 10% humidity environment; Assembly: The battery was assembled in an argon atmosphere glove box. Ten batteries were assembled in each group and allowed to stand for 1 hour after packaging.

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