Capacity grading screening method for improving cycle performance of energy storage sodium ion battery

Abstract

The invention discloses a capacity grading screening method for improving the cycle performance of an energy storage sodium-ion battery, and belongs to the technical field of performance improvement of sodium-ion batteries. The capacity grading screening method comprises the following steps: S100, placing a battery in a capacity grading system, and carrying out a constant-power charging and discharging capacity grading step; and S200, after the capacity grading step is finished, capacity, internal resistance, self-discharge and tail end voltage screening and grading are carried out respectively. 0.5 P constant power charging and discharging are adopted, the battery capacity grading step is consistent with the application end, capacity grading data can more accurately reflect the battery state of the application end, the capacity grading method detects and screens the polarization voltage of the charging and discharging tail ends, the consistency of energy storage battery grouping can be improved, the voltage difference of the charging and discharging tail ends of a module / whole package system is reduced, and the battery capacity grading efficiency is improved. And the cycle performance of the energy storage system is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of improving the performance of sodium-ion batteries, and particularly relates to a grading and screening method for improving the cycle performance of energy storage sodium-ion batteries. Background Art

[0002] Due to excellent high and low temperature performance, safety performance, and low cost, sodium-ion batteries have broad application prospects in the field of new energy storage. To meet diverse power and capacity requirements, energy storage battery modules usually need to be realized through series and parallel configurations of multiple battery cells, which places high requirements on the electrochemical performance consistency among the battery cells in the electrical distribution group.

[0003] Currently, whether it is lithium batteries or sodium batteries, grading and screening still adopt constant current charge and discharge steps, and the screened electrical properties mainly include capacity, AC internal resistance, self-discharge rate, and voltage. However, the application side of energy storage modules uses constant power charge and discharge, so constant current grading and screening cannot effectively reflect the actual situation of the battery application side; at the same time, the terminal voltage difference during charge and discharge at the application side of the module has a great impact on the capacity, cycle, and even safety performance of the battery pack, and there will be an edge phenomenon of the barrel effect, resulting in unqualified module capacity or poor cycle performance. The reasons for unqualified module capacity are as follows: ① During grading and screening with constant current and constant voltage, the polarization at the end of charge and discharge is smaller than that of constant power charge and discharge, resulting in a larger capacity for constant current and constant voltage charge and discharge than that of constant power charge and discharge, and the grading and screening capacity cannot well reflect the module capacity; ② Since the module stops when the monomer voltage reaches the set upper and lower limits, the energy capacity of one battery is unqualified due to a large terminal voltage difference; if the module voltage is based on the overall voltage upper limit, the battery with a large terminal voltage difference will be overcharged or over-discharged. Although the capacity is qualified in this case, the cycle performance is poor and there will be safety risks.

[0004] Therefore, how to screen batteries during the monomer manufacturing process to more effectively reflect the actual application situation of energy storage module batteries and improve the capacity and cycle performance of the module application side is a problem. Summary of the Invention

[0005] The purpose of the present invention is to provide a grading and screening method for improving the cycle performance of energy storage sodium-ion batteries to solve the problems of poor capacity and cycle performance of sodium-ion battery modules.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A grading and screening method for improving the cycle performance of energy storage sodium-ion batteries includes the following steps:

[0008] S100: Place the battery in a grading and screening system to perform a constant power charge and discharge grading and screening step;

[0009] S200: After the grading and screening step is completed, perform capacity, internal resistance, self-discharge, and terminal voltage screening and grading respectively.

[0010] As a further solution of the present invention, the step S100 includes:

[0011] S101: Charge at a constant power until the cut-off voltage V max ;

[0012] S102: Stand still for a preset time T1;

[0013] S103: Discharge at a constant power until the cut-off voltage V min ;

[0014] S104: Stand still for a preset time T1;

[0015] S105: Charge at a constant power until the cut-off voltage V max ;

[0016] S106: Stand still for a preset time T1, record the starting voltage V 11 at the start of standing still and the ending voltage V 12 ;

[0017] S107: Discharge at a constant power until the cut-off voltage V min , record the discharge capacity Q;

[0018] S108: Stand still for a preset time T1, record the starting voltage V 21 at the start of standing still and the ending voltage V 22 ;

[0019] S109: Charge at a constant power, adjust the SOC (state of charge) of the battery, and stand still for a preset time T2.

[0020] As a further solution of the present invention, the constant power is 0.33P - 1P, the constant power mode is adopted during the charge and discharge process, and the charge and discharge power is consistent with the power at the battery application end.

[0021] As a further solution of the present invention, the preset standing still time T1 is 0 - 30 min.

[0022] As a further solution of the present invention, the preset standing still time T2 is 0 - 60 min.

[0023] As a further solution of the present invention, the value of the SOC is 70% - 80%.

[0024] As a further solution of the present invention, in the step S100, the grading capacitance system automatically calculates the ohmic polarization voltage difference V a at the end of charging and the concentration polarization voltage difference V b , V a = V max - V 11 Vb = V 11 -V 12 。

[0025] As a further solution of the present invention, the ohmic polarization pressure difference V a and the concentration polarization pressure difference V b at the charging end are divided into grades, with one grade for 5 mV - 50 mV.

[0026] As a further solution of the present invention, in the step S100, the grading system automatically calculates the ohmic polarization pressure difference V c and the concentration polarization pressure difference V d at the discharging end, V c = V 21 -V min ,V d = V 22 -V 21 。

[0027] As a further solution of the present invention, the ohmic polarization pressure difference V c and the concentration polarization pressure difference V d at the discharging end are divided into grades, with one grade for 30 mV - 200 mV.

[0028] As a further solution of the present invention, in the step S200, during the capacity screening and grading, the capacity uses the discharging capacity Q as the screening criterion.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. The present invention provides a grading and screening method for improving the cycle performance of energy storage sodium-ion batteries. Through comprehensive tests of multiple charge and discharge cycles, rest time, and performance parameters, the cycle performance and stability of sodium-ion batteries can be effectively improved. In this way, batteries with excellent performance can be screened out to meet the requirements of energy storage systems for high-performance batteries. The grading method described in the present invention uses a constant power charge and discharge of 0.33P - 1P. The battery grading process is consistent with the application end, and the grading data can more accurately reflect the battery state at the application end. The grading method detects and screens the polarization voltage at the charge and discharge ends, which can improve the consistency of energy storage battery grouping, reduce the charge and discharge end pressure difference of the module / entire package system, and thus improve the cycle performance of the energy storage system.

[0031] 2. The formation process of single cells is consistent with the application side of the whole module. The formation process data and capacity can better reflect the true condition of the batteries in the module. Detect the voltages at the charging and discharging ends during the formation process and use them as a judgment criterion during the single cell screening process, which can control the voltage difference at the charging and discharging ends between the batteries within an appropriate range during module matching, and avoid the phenomena of low overall capacity and poor cycling performance caused by excessive voltage difference at the ends during module charging and discharging. Description of the Drawings

[0032] The present invention will be further described below with reference to the drawings.

[0033] Figure 1 It is the 0.5P cycle discharge curve diagram of the series module composed of 5 qualified batteries screened in Embodiment 1 of the present invention.

[0034] Figure 2 It is the 0.5P cycle discharge curve diagram of the series module composed of 5 qualified batteries screened in Comparative Example 1 of the present invention. Detailed Embodiments

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0036] Obviously, the following description is only some examples or embodiments of the present application. For those of ordinary skill in the art, without creative efforts, the present application can also be applied to other similar scenarios. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present application, some designs, manufacturing or production changes based on the technical content disclosed in the present application are only conventional technical means and should not be understood that the content disclosed in the present application is insufficient.

[0037] However, there will be cases where unnecessary detailed descriptions are omitted. For example, there are cases where the detailed descriptions of well-known matters are omitted and the repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the following description is provided for those skilled in the art to fully understand the present application and is not intended to limit the subject matter recited in the claims.

[0038] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0039] The following examples and comparative examples perform grading and screening on the layered oxygen P-phase energy storage sodium-ion battery. The nominal capacity of the layered oxygen P-phase energy storage sodium-ion battery is 70 Ah, the voltage range is 2.0 V - 4.2 V, the nominal energy of a single battery is 238 Wh, and the application scenario of the energy storage integrated package is constant power charge and discharge at 0.5P.

[0040] Example 1

[0041] A grading and screening method for improving the cycle performance of an energy storage sodium-ion battery, comprising the following steps:

[0042] S100: Place the battery in a grading system for the grading step;

[0043] S101: Charge at a constant power of 0.5P (169 Wh) to the cut-off voltage V max = 4.2 V;

[0044] S102: Stand still for a preset time T1 = 5 min;

[0045] S103: Discharge at a constant power of 0.5P (169 Wh) to the cut-off voltage V min = 2.0 V;

[0046] S104: Stand still for a preset time T1 = 5 min;

[0047] S105: Charge at a constant power of 0.5P (169 Wh) to the cut-off voltage V max = 4.2 V;

[0048] S106: Stand still for a preset time T1 = 5 min, record the starting voltage V 11 and the ending voltage V 12 ;

[0049] S107: Discharge at a constant power of 0.5P (169 Wh) to the cut-off voltage V min = 2.0 V, record the discharge capacity Q;

[0050] S108: Stand still for a preset time T1 = 5 min, record the starting voltage V 21 and the ending voltage V 22 ;

[0051] S109: Charge at a constant power of 0.5P (169 Wh) for a certain time, adjust the battery to 75% SOC, and stand still for a preset time T2 = 30 min;

[0052] S200: After the formation step, capacity, internal resistance, self-discharge, and end voltage screening and grading are carried out respectively.

[0053] Take 5 batteries that pass the screening to form a series module, and conduct three cycles of 0.5P constant power cycling test. The discharge curves of the five batteries are consistent, and the module capacity is qualified.

[0054] Example 2

[0055] A formation and screening method for improving the cycling performance of energy storage sodium-ion batteries, comprising the following steps:

[0056] S100: Place the battery in a formation system to perform the formation step;

[0057] S101: Charge at a constant power of 0.5P (169 Wh) to the cut-off voltage V max = 4.2 V;

[0058] S102: Stand still for a preset time T1 = 15 min;

[0059] S103: Discharge at a constant power of 0.5P (169 Wh) to the cut-off voltage V min = 2.0 V;

[0060] S104: Stand still for a preset time T1 = 15 min;

[0061] S105: Charge at a constant power of 0.5P (169 Wh) to the cut-off voltage V max = 4.2 V;

[0062] S106: Stand still for a preset time T1 = 15 min, record the starting voltage V 11 and the ending voltage V 12 ;

[0063] S107: Discharge at a constant power of 0.5P (169 Wh) to the cut-off voltage V min = 2.0 V, record the discharge capacity Q;

[0064] S108: Stand still for a preset time T1 = 15 min, record the starting voltage V 21 and the ending voltage V 22 ;

[0065] S109: Charge at a constant power of 0.5P (169 Wh) for a certain time, adjust the battery to 75% SOC, and stand still for a preset time T2 = 10 min;

[0066] S200: After the formation step, capacity, internal resistance, self-discharge, and end voltage screening and grading are carried out respectively.

[0067] Take 5 qualified batteries to form a series module and conduct three cycles of constant power cycling test at 0.5P. The discharge curves of the five batteries are consistent and the module capacity is qualified.

[0068] Example 3

[0069] A grading and screening method for improving the cycle performance of sodium-ion energy storage batteries, comprising the following steps:

[0070] S100: Place the battery in a grading system for grading steps;

[0071] S101: Charge at a constant power of 0.5P (169 Wh) to the cut-off voltage V max = 4.2 V;

[0072] S102: Stand still for a preset time T1 = 30 min;

[0073] S103: Discharge at a constant power of 0.5P (169 Wh) to the cut-off voltage V min = 2.0 V;

[0074] S104: Stand still for a preset time T1 = 30 min;

[0075] S105: Charge at a constant power of 0.5P (169 Wh) to the cut-off voltage V max = 4.2 V;

[0076] S106: Stand still for a preset time T1 = 30 min, record the starting voltage V 11 at the start of standing still and the ending voltage V 12 ;

[0077] S107: Discharge at a constant power of 0.5P (169 Wh) to the cut-off voltage V min = 2.0 V, record the discharge capacity Q;

[0078] S108: Stand still for a preset time T1 = 30 min, record the starting voltage V 21 at the start of standing still and the ending voltage V 22 ;

[0079] S109: Charge at a constant power of 0.5P (169 Wh) for a certain period of time, adjust the battery to 75% SOC, and stand still for a preset time T2 = 50 min;

[0080] S200: After the grading steps are completed, perform capacity, internal resistance, self-discharge, and end voltage screening and grading respectively.

[0081] Take 5 qualified batteries to form a series module and conduct three cycles of constant power cycling test at 0.5P. The discharge curves of the five batteries are consistent and the module capacity is qualified.

[0082] Example 4

[0083] A grading and screening method for improving the cycle performance of energy storage sodium-ion batteries, comprising the following steps:

[0084] S100: Place the battery in a grading and screening system for the grading and screening process;

[0085] S101: Charge at a constant power of 0.5P (169 Wh) to the cut-off voltage V max = 4.2 V;

[0086] S102: Stand still for a preset time T1 = 5 min;

[0087] S103: Discharge at a constant power of 0.5P (169 Wh) to the cut-off voltage V min = 2.0 V;

[0088] S104: Stand still for a preset time T1 = 5 min;

[0089] S105: Charge at a constant power of 0.5P (169 Wh) to the cut-off voltage V max = 4.2 V;

[0090] S106: Stand still for a preset time T1 = 5 min, record the starting voltage V 11 and the ending voltage V 12 ;

[0091] S107: Discharge at a constant power of 0.5P (169 Wh) to the cut-off voltage V min = 2.0 V, record the discharge capacity Q;

[0092] S108: Stand still for a preset time T1 = 5 min, record the starting voltage V 21 and the ending voltage V 22 ;

[0093] S109: Charge at a constant power of 0.5P (169 Wh) for a certain period of time, adjust the battery to 70% SOC, and stand still for a preset time T2 = 30 min;

[0094] S200: After the grading and screening process is completed, perform capacity, internal resistance, self-discharge, and end voltage screening and grading respectively.

[0095] Take 5 batteries that pass the screening to form a series module, and perform three cycles of 0.5P constant power cycle testing. The discharge curves of the five batteries are consistent, and the module capacity is qualified.

[0096] Example 5

[0097] A grading and screening method for improving the cycle performance of energy storage sodium-ion batteries, comprising the following steps:

[0098] S100: Place the battery in a grading and forming system for the grading and forming step;

[0099] S101: Charge at a constant power of 0.5P (169 Wh) to the cut-off voltage V max = 4.2 V;

[0100] S102: Stand still for a preset time T1 = 5 min;

[0101] S103: Discharge at a constant power of 0.5P (169 Wh) to the cut-off voltage V min = 2.0 V;

[0102] S104: Stand still for a preset time T1 = 5 min;

[0103] S105: Charge at a constant power of 0.5P (169 Wh) to the cut-off voltage V max = 4.2 V;

[0104] S106: Stand still for a preset time T1 = 5 min, record the starting voltage V 11 and the ending voltage V 12 ;

[0105] S107: Discharge at a constant power of 0.5P (169 Wh) to the cut-off voltage V min = 2.0 V, record the discharge capacity Q;

[0106] S108: Stand still for a preset time T1 = 5 min, record the starting voltage V 21 and the ending voltage V 22 ;

[0107] S109: Charge at a constant power of 0.5P (169 Wh) for a certain time, adjust the battery to 80% SOC, and stand still for a preset time T2 = 30 min;

[0108] S200: After the grading and forming step, perform capacity, internal resistance, self-discharge, and end voltage screening and grading respectively.

[0109] Take 5 batteries that pass the screening to form a series module, and perform three cycles of 0.5P constant power cycling test. The discharge curves of the five batteries are consistent, and the module capacity is qualified.

[0110] Comparative Example 1

[0111] A grading and screening method for the cycling performance of a sodium-ion battery, comprising the following steps:

[0112] S100: Place the battery in a grading and forming system for the grading and forming step;

[0113] S101: Constant current and constant voltage charge a 35 Ah battery to 4.2 V with a cut-off current of 3.5 Ah;

[0114] S102: Stand still for a preset time T1 = 5 min;

[0115] S103: Constant current and constant voltage discharge a 35 Ah battery to 2.0 V;

[0116] S104: Stand still for a preset time T1 = 5 min;

[0117] S105: Constant current and constant voltage charge a 35 Ah battery to 4.2 V with a cut-off current of 3.5 Ah;

[0118] S106: Stand still for a preset time T1 = 5 min;

[0119] S107: Constant current and constant voltage discharge a 35 Ah battery to 2.0 V and record the discharge capacity Q;

[0120] S108: Stand still for a preset time T1 = 5 min;

[0121] S109: Constant current and constant voltage charge a 35 Ah battery to 3.85 V with a cut-off current of 3.5 Ah and stand still for a preset time T2 = 30 min;

[0122] S200: After the grading process ends, perform capacity, internal resistance, and self-discharge screening and grading respectively.

[0123] Take 5 batteries that pass the screening to form a series module and conduct three cycles of 0.5P constant power cycling test. The end voltage of one battery during charge and discharge is too large, resulting in this battery being shallowly charged and discharged, while the other 4 batteries are fully charged and shallowly discharged, and the overall module capacity is unqualified.

[0124] Comparative Example 2

[0125] A grading and screening method for the cycle performance of a sodium-ion battery, comprising the following steps:

[0126] S100: Place the battery in a grading system for the grading process;

[0127] S101: Charge at a constant power of 0.5P (169 Wh) to the cut-off voltage V max = 4.2 V;

[0128] S102: Stand still for a preset time T1 = 40 min;

[0129] S103: Discharge at a constant power of 0.5P (169 Wh) to the cut-off voltage V min = 2.0 V;

[0130] S104: Stand still for a preset time T1 = 40 min;

[0131] S105: Charge at a constant power of 0.5P (169 Wh) until the cut-off voltage V max = 4.2 V;

[0132] S106: Stand still for a preset time T1 = 40 min, and record the starting voltage V 11 at the start of standing still and the ending voltage V 12 ;

[0133] S107: Discharge at a constant power of 0.5P (169 Wh) until the cut-off voltage V min = 2.0 V, and record the discharge capacity Q;

[0134] S108: Stand still for a preset time T1 = 5 min, and record the starting voltage V 21 at the start of standing still and the ending voltage V 22 ;

[0135] S109: Charge at a constant power of 0.5P (169 Wh) for a certain period of time, adjust the battery to 75% SOC, and stand still for a preset time T2 = 80 min;

[0136] S200: After the grading step is completed, perform capacity, internal resistance, self-discharge, and terminal voltage screening and grading respectively.

[0137] Take 5 batteries that pass the screening to form a series module and conduct three cycles of 0.5P constant power cycle testing. The terminal voltage at the charge and discharge of one battery is relatively large, resulting in this battery being shallowly charged and discharged, while the other 4 batteries are fully charged and shallowly discharged, and the overall module capacity is unqualified.

[0138] The relevant parameters in the above embodiments and comparative examples are summarized in Table 1.

[0139] Table 1

[0140] Constant power <![CDATA[Let stand for a preset time T1]]> <![CDATA[Let it stand for a preset time T2]]> SOC Whether qualified Example 1 0.5P 5 min 30 min 75％ Qualified Example 2 0.5P 15 min 10 min 75％ Qualified Example 3 0.5P 30 min 50 min 75％ Qualified Example 4 0.5P 5 min 30 min 70％ Qualified Example 5 0.5P 5 min 30 min 80％ Qualified Comparative example 1 / 5 min 30 min / Unqualified Comparative example 2 0.5P 40 min 80 min 75％ Unqualified

[0141] In Example 1, constant power charge and discharge are used for grading, and the screening conditions are increased to include screening of the terminal voltage at charge and discharge. In Comparative Example 1, constant current constant voltage charging @ constant current discharge is used for grading, and normal screening (capacity / internal resistance / self-discharge) is performed. The comparison of the screening conditions between Example 1 and Comparative Example 1 is shown in Table 2.

[0142] Table 2

[0143]

[0144] The comparison of the 0.5P cycle capacity of the series modules composed of 5 qualified batteries screened in Example 1 and Comparative Example 1 is shown in Table 3; the 0.5P cycle discharge curve of the series module composed of 5 qualified batteries screened in Example 1 is as Figure 1 shown, and the 0.5P cycle discharge curve of the series module composed of 5 qualified batteries screened in Comparative Example 1 is asFigure 2 as shown

[0145] Table 3

[0146]

[0147]

[0148] As can be seen from the above test results, the present invention detects the voltages at the ends of charge and discharge during the formation process and uses them as a judgment criterion in the single-cell screening process, so as to control the voltage difference at the ends of charge and discharge between each battery within a suitable range during module matching, and avoid the phenomena of low overall capacity and poor cycle performance caused by excessive voltage difference at the ends during the charge and discharge process of the module.

[0149] It should be noted that, in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0150] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A grading and screening method for improving the cycling performance of energy storage sodium-ion batteries, characterized in that, Including the following steps: S100: Place the battery in a grading and forming system to perform a constant power charge and discharge grading process step; S200: After the grading process step is completed, perform capacity, internal resistance, self-discharge, and end voltage screening and grading respectively.

2. The grading and screening method for improving the cycle performance of a sodium-ion energy storage battery according to claim 1, wherein The S100 includes: S101: Charge at a constant power until the cut-off voltage V max ; S102: Stand still for a preset time T1; S103: Discharge at a constant power until the cut-off voltage V min ; S104: Stand still for a preset time T1; S105: Constant power charging to the cut-off voltage V max ; S106: Let it stand for a preset time T1, and record the starting voltage V during standing 11 and the ending voltage V during standing 12 ; S107: Discharge at a constant power until the cut-off voltage V min , and record the discharge capacity Q; S108: Let it stand for a preset time T1, and record the initial standing voltage V 21 and the final standing voltage V 22 ; S109: Charge at a constant power, adjust the SOC of the battery, and stand still for a preset time T2.

3. A grading and screening method for improving the cycle performance of a sodium-ion energy storage battery according to claim 1, characterized in that The constant power is 0.33P - 1P. The constant power mode is adopted during the charge and discharge process, and the charge and discharge power is consistent with the power at the battery application end.

4. A grading and screening method for improving the cycle performance of a sodium-ion energy storage battery according to claim 2, characterized in that The preset standing still time T1 is 0 - 30 min; the preset standing still time T2 is 0 - 60 min.

5. A grading and screening method for improving the cycle performance of a sodium-ion energy storage battery according to claim 2, characterized in that The magnitude of the SOC is 70% - 80%.

6. The grading and screening method for improving the cycle performance of a sodium-ion energy storage battery according to claim 1, wherein In the S100, the grading and forming system automatically calculates the ohmic polarization voltage difference V a and the concentration polarization voltage difference V b .

7. A grading and screening method for improving the cycle performance of a sodium-ion energy storage battery according to claim 6, characterized in that, The ohmic polarization voltage difference V of the charging terminal a and the concentration polarization voltage difference V b are grouped into grades, with one grade for 5 mV - 50 mV.

8. A grading and screening method for improving the cycle performance of a sodium-ion energy storage battery according to claim 1, characterized in that, In the S100, the grading and forming system automatically calculates the ohmic polarization pressure difference V c and the concentration polarization pressure difference V d .

9. A grading and screening method for improving the cycle performance of a sodium-ion energy storage battery according to claim 8, characterized in that, The ohmic polarization voltage difference V of the discharge end c and the concentration polarization voltage difference V d are grouped into ranges of 30 mV - 200 mV per range.

10. A grading and screening method for improving the cycle performance of a sodium-ion energy storage battery according to claim 1, characterized in that In the S200, during the capacity screening and grading, the capacity Q of the discharge is used as the screening criterion for the capacity.

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