Method for calculating manganese-iron ratio of positive electrode in lithium manganese iron phosphate battery

Abstract

The invention provides a method for calculating the manganese-iron ratio of a positive electrode in a manganese-iron-lithium phosphate battery. The method comprises the following steps: S1, carrying out a first charge-discharge test on the manganese-iron-lithium phosphate battery to obtain first coulombic efficiency a; s2, the lithium manganese iron phosphate battery is subjected to direct current internal resistance testing, an SOC-DCR curve is obtained, and the SOC value of a sudden change point in the SOC-DCR curve is b; s3, the amount of substance of manganese atoms in the positive electrode is expressed by NMn, the amount of substance of iron atoms in the positive electrode is expressed by NFe, and the manganese-iron ratio is calculated through the following relational expression: # imgabs0 #. The method for testing the manganese-iron ratio of the positive electrode in the lithium manganese iron phosphate battery is free of damage to a battery cell, efficient, convenient and low in cost.

Description

Technical Field

[0001] The invention belongs to the field of lithium manganese iron phosphate batteries, and in particular relates to a method for calculating the manganese-iron ratio of a positive electrode in a lithium manganese iron phosphate battery. Background Art

[0002] As a new type of cathode material, lithium manganese iron phosphate (LMFP) has both the safety of lithium iron phosphate (LFP) and higher energy density. Therefore, in recent years, with the development of battery technology and the growth of market demand, lithium manganese iron phosphate has received widespread attention and is regarded as a potential upgrade path for lithium iron phosphate.

[0003] However, there is a large gap in the physical and chemical properties of lithium iron phosphate materials with different manganese-iron ratios. Theoretically, as the manganese atom content in lithium iron phosphate materials increases, the average voltage of lithium iron phosphate batteries using them will increase, thereby increasing the energy density of lithium iron phosphate batteries. In addition, the inherent Jahn-Teller effect of lithium iron phosphate materials can cause the collapse of their crystal structure, causing manganese elements to be deposited on the negative electrode, thereby catalyzing the decomposition of the SEI film and causing irreversible attenuation of cycle performance.

[0004] Therefore, calculating the manganese-iron ratio of a battery cell with an unknown manganese-iron ratio is of great significance for studying the stability of the crystal structure and even for the research and design of the battery cell and BMS. At present, in the prior art, the means for detecting the manganese-iron ratio in the battery cell is generally the inductively coupled plasma emission spectrometer (ICP) technology. ICP has the advantages of high precision, low detection limit and high sensitivity, so that it can accurately detect the manganese and iron elements in the battery cell. However, the ICP technology is to dissolve the powder in a solvent before testing. For a newly assembled new battery, the battery cell must be disassembled and the LMFP powder must be scraped out for testing, which will cause irreversible damage to the battery cell. At the same time, ICP detection equipment is expensive, the testing cost is high, and the testing process is cumbersome. In summary, in the current prior art, the steps required to obtain the ratio of manganese and iron elements in the battery cell are cumbersome, which not only wastes time, but also consumes relatively high costs. Summary of the invention

[0005] In order to solve the problem in the prior art that the manganese-iron ratio of the positive electrode needs to be tested by disassembling the battery, the present application provides a method for calculating the manganese-iron ratio of the positive electrode in a lithium manganese iron phosphate battery.

[0006] In a first aspect of the present application, a method for calculating the manganese-iron ratio of the positive electrode in a lithium manganese iron phosphate battery is provided, the method comprising the following steps: S1. performing a first charge and discharge test on the lithium manganese iron phosphate battery to obtain a first coulomb efficiency a; S2. subsequently performing a DC internal resistance test on the lithium manganese iron phosphate battery to obtain a SOC-DCR curve, wherein the SOC value of the mutation point in the SOC-DCR curve is b; S3. Mn It indicates the amount of manganese atoms in the positive electrode, expressed as N Fe Represents the amount of iron atoms in the positive electrode, and the manganese-iron ratio is calculated by the following relationship:

[0007] During the discharge process of lithium manganese iron phosphate battery, Li + It will be embedded in the site corresponding to the Mn site first, and then in the site corresponding to the Fe site. Therefore, the discharge curve of the lithium manganese iron phosphate material in the lithium manganese iron phosphate battery presents two voltage platforms, corresponding to Mn and Fe respectively. 2+ / Mn 3+ (about 4.1V vs.Li / Li + ) and Fe 2+ / Fe 3+ (about 3.6V vs.Li / Li + ). Therefore, there will be a sudden increase point in the DCR curve of the lithium manganese iron phosphate battery, which corresponds to the separation point of the above two platforms. The inventors found that the difference in Mn / Fe ratio in the lithium manganese iron phosphate battery will affect the length of the two voltage platforms on the discharge curve and also affect the position of the sudden increase point of the DCR curve. Therefore, this application will perform lossless manganese iron ratio calculation based on this characteristic.

[0008] Specifically, the inventors found by observing the discharge curve that the two voltage platforms presented by the discharge curve indicate that after removing some lithium ions that are preferentially embedded and completely occupy the manganese position, the remaining lithium ions will occupy the iron position. Therefore, in an ideal situation, since there is no loss of active lithium, in order to calculate Mn / Fe, the lithium content occupying the Mn position can be directly compared with the lithium content occupying the Fe position. However, in actual situations, there will be a problem of irreversible loss of lithium during the first charge and discharge.

[0009] The inventors have discovered through experiments that the active lithium loss of all lithium ions released from the positive electrode during charging can be represented by (1-a). In lithium manganese iron phosphate batteries, lithium ions will first completely occupy the manganese position before occupying the iron position. Therefore, in actual situations, due to the problem of irreversible lithium loss during the first charge and discharge, some iron positions that should have been occupied by lithium ions are not occupied, and this part of iron can be represented by the active lithium loss. Therefore, the ratio of the lithium content occupying the Mn position to the sum of the lithium content occupying the Fe position and the irreversible lithium loss content during the first charge and discharge is the ratio of the Mn / Fe elements.

[0010] Therefore, the inventors assumed that the initial total lithium content of the lithium manganese iron phosphate material in the lithium manganese iron phosphate battery is C, and the manganese-iron ratio can be expressed by formula (1). After sorting, formula (2) can be obtained. It can be seen from formula (2) that the manganese-iron ratio can be calculated by knowing the first coulomb efficiency a and the SOC value b corresponding to the DCR mutation point.

[0011]

[0012]

[0013] The test method provided in this application first performs a charge and discharge test on the battery to obtain the initial efficiency data for calculating the irreversible loss of active lithium (at this time, two Mn 2+ / Mn 3+ and Fe 2+ / Fe 3+ The redox reaction consumes active lithium to produce SEI film on the negative electrode surface, resulting in irreversible capacity loss). Subsequently, the battery cell is subjected to a DCR test to draw a SOC-DCR curve to determine the SOC value at the above-mentioned sudden increase point, and Mn / Fe can be calculated by substituting it into the formula. Therefore, the present application provides a convenient, fast, low-cost method for obtaining Mn / Fe in lithium manganese iron phosphate batteries without disassembling the battery.

[0014] Preferably, in S2, the data collection of the SOC-DCR curve includes the following steps: S21. The lithium manganese iron phosphate battery is heated to 45-60°C, and activated after standing. The lithium manganese iron phosphate battery is subjected to cyclic charge and discharge, thereby measuring the discharge capacity Q0 of the lithium manganese iron phosphate battery; S22. Subsequently, the lithium manganese iron phosphate battery is charged to make its SOC0=100%, and after standing, it is subjected to a constant current discharge treatment for 8-12 seconds, and its discharge capacity Q1 is recorded and the DCR value when SOC0=100% is obtained; S23. The lithium manganese iron phosphate battery is charged and discharged. Perform a static treatment, and then perform a constant current discharge treatment with a cut-off capacity of c×Q0-Q1, wherein c is any real number between 0 and 100%; S24. Then, after the static treatment, perform a constant current discharge treatment for 8 to 12 seconds until the SOC value of the lithium manganese iron phosphate battery reaches SOC1 and measure the DCR value of the lithium manganese iron phosphate battery in this state, wherein SOC1=100%-(c×Q0-Q1); S25. Repeat S23 and S24, and construct the SOC-DCR curve using the SOC value and its corresponding DCR value measured in each repetition of the S24 process.

[0015] Preferably, in S25, S23 and S24 are repeated until

[0016] Preferably, c is not higher than 5%.

[0017] Preferably, 1.5%≤c≤2.5%.

[0018] Preferably, in S21, the temperature of the lithium manganese iron phosphate battery is raised to 50-55°C.

[0019] Preferably, in S21, the activation treatment is: constant current and constant voltage charging under the reaction conditions of current of 0.1-1C, voltage of 4.0-4.3V, and cut-off current of 0.01-0.1C, and then the lithium manganese iron phosphate battery is subjected to a static treatment and constant current discharge under the reaction conditions of current of 0.1-1C and cut-off voltage of 2.0-3.0V.

[0020] Preferably, the operation of cycle S21 is cycled 1 to 5 times, and the last discharge capacity is Q0.

[0021] Preferably, in S21, the standing time of the standing treatment is 3 to 10 minutes.

[0022] Preferably, in S22, the standing time of the standing treatment is 0.5 to 1.5 hours.

[0023] Preferably, in S23, the standing time of the standing treatment is 3 to 10 minutes.

[0024] Preferably, in S24, the standing time of the standing treatment is 0.5 to 1.5 hours.

[0025] Preferably, the first charge and discharge test comprises the following steps: S11. The lithium manganese iron phosphate battery is subjected to constant current and constant voltage charging treatment under the reaction conditions of current of 0.05-0.15C, voltage of 4.0-4.3V, and cut-off current of 0.01-1C to obtain the charging capacity; S12. The lithium manganese iron phosphate battery is subjected to a static treatment, and then subjected to a constant current discharge treatment under the reaction conditions of current of 0.05-0.15C, and cut-off voltage of 2.0-3.0V to obtain the discharge capacity, and then the discharge capacity is obtained by the formula Get the first coulombic efficiency a.

[0026] Preferably, a is a real number between 0 and 100%.

[0027] Preferably, in the lithium manganese iron phosphate battery, N Mn 、N Fe The following relationship is satisfied: When the manganese content and iron content of the lithium manganese iron phosphate battery satisfy the above relationship, the accuracy of the method can be further improved.

[0028] Preferably, the amount of lithium atoms is NLi , the amount of substance of phosphorus atom is N P In the lithium manganese iron phosphate battery, the following relationship is satisfied: 0.95≤N Li / N P ≤1.10; and / or, 0.9≤(N Mn +N Fe ) / N P ≤1.15; and / or, 1.01≤N Li / (N Mn +N Fe )≤1.10. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the SOC-DCR diagram provided in Example 4 of the present application. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in this application will be clearly and completely described below in conjunction with the embodiments of this application and the drawings in the embodiments. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0031] Example 1

[0032] S1. Performing charge and discharge tests on the above-mentioned lithium manganese iron phosphate battery to obtain the first coulombic efficiency a;

[0033] S2. Then, the lithium manganese iron phosphate battery is subjected to a DC internal resistance test to obtain a SOC-DCR curve, wherein the SOC value at the mutation point in the SOC-DCR curve is b;

[0034] S3. With Mn as the manganese content and Fe as the iron content, the ratio of manganese to iron is calculated by the following relationship:

[0035] Specifically, the process steps of the first-effect charge and discharge test are as follows:

[0036] S11. The lithium manganese iron phosphate battery was charged at a constant current and constant voltage with a current of 0.1C, a voltage of 4.2V, and a cut-off current of 0.05C to obtain a charge capacity;

[0037] S12. The lithium manganese iron phosphate battery was left to stand for 5 minutes, and then subjected to constant current discharge treatment under the reaction conditions of a current of 0.1C and a cut-off voltage of 2V to obtain the discharge capacity, and then the formula was used to calculate Get the first coulombic efficiency a.

[0038] Specifically, the test temperature of the DC internal resistance test is 40±2°C, and the specific process steps are:

[0039] S21. The lithium manganese iron phosphate battery is heated to 40°C, and after standing for 5 minutes, it is charged at a constant current and constant voltage under the reaction conditions of a current of 0.5C, a voltage of 4.2V, and a cut-off current of 0.05C. Then, after the lithium manganese iron phosphate battery is stood for 5 minutes, it is discharged at a constant current under the reaction conditions of a current of 0.5C and a cut-off voltage of 2V. The above operation is cycled 3 times, and the last discharge capacity is taken as Q0;

[0040] S22. Then, after standing for 5 minutes, the lithium manganese iron phosphate battery was charged with constant current and constant voltage under the reaction conditions of current of 0.5C, voltage of 4.2V, and cut-off current of 0.05C, so that its SOC0=100%; then, after standing for 1 hour, it was discharged with constant current under the reaction conditions of current of 1C and cut-off voltage of 2V for 10 seconds, and its discharge capacity Q1 was recorded and the DCR value at SOC0=100% was obtained (according to Ohm's law, the DCR value under the corresponding SOC can be obtained by dividing the voltage difference by the constant current);

[0041] S23. After the lithium manganese iron phosphate battery has been left to stand for 5 minutes, a constant current discharge treatment is performed at a current of 0.5C and a cut-off capacity of c×Q0-Q1 to adjust the SOC of the lithium manganese iron phosphate battery, where c=2%;

[0042] S24. After standing for 1 hour, the battery was discharged at a constant current of 1C and a cut-off voltage of 2V for 10 seconds to obtain the DCR value when SOC1 = 100% - (c × Q0-Q1);

[0043] S25. Repeat S23 and S24 until Specifically, reference may be made to the process steps shown in Table 1. In the lithium manganese iron phosphate battery used in this embodiment, N Mn 、N Fe Satisfy N Mn / (N Mn +N Fe )=1.5.

[0044] Table 1. DC internal resistance test process steps

[0045]

[0046] Example 2

[0047] This embodiment calculates the ratio of manganese to iron in the lithium manganese iron phosphate battery with reference to the method provided in Embodiment 1. The difference from Embodiment 1 is that the test temperature is 45°C when the DC internal resistance test is performed in this embodiment. Except for the above difference, the operation steps for calculating the ratio of manganese to iron in the lithium manganese iron phosphate battery in this embodiment are strictly consistent with those in Embodiment 1.

[0048] Example 3

[0049] This embodiment calculates the ratio of manganese to iron in the lithium manganese iron phosphate battery with reference to the method provided in Embodiment 1. The difference from Embodiment 1 is that the test temperature is 50°C when the DC internal resistance test is performed in this embodiment. Except for the above difference, the operation steps for calculating the ratio of manganese to iron in the lithium manganese iron phosphate battery in this embodiment are strictly consistent with those in Embodiment 1.

[0050] Example 4

[0051] This embodiment calculates the ratio of manganese to iron in the lithium manganese iron phosphate battery with reference to the method provided in Embodiment 1. The difference from Embodiment 1 is that the test temperature is 55°C when the DC internal resistance test is performed in this embodiment. Except for the above difference, the operation steps for calculating the ratio of manganese to iron in the lithium manganese iron phosphate battery in this embodiment are strictly consistent with those in Embodiment 1.

[0052] Example 5

[0053] This embodiment calculates the ratio of manganese to iron in the lithium manganese iron phosphate battery with reference to the method provided in Embodiment 1. The difference from Embodiment 1 is that the test temperature is 60°C when the DC internal resistance test is performed in this embodiment. Except for the above difference, the operation steps for calculating the ratio of manganese to iron in the lithium manganese iron phosphate battery in this embodiment are strictly consistent with those in Embodiment 1.

[0054] Example 6

[0055] This embodiment calculates the ratio of manganese to iron in the lithium manganese iron phosphate battery with reference to the method provided in Embodiment 4. The difference from Embodiment 4 is that in this embodiment, when performing the DC internal resistance test, c=1%. Except for the above difference, the operation steps for calculating the ratio of manganese to iron in the lithium manganese iron phosphate battery in this embodiment are strictly consistent with those in Embodiment 4.

[0056] Example 7

[0057] This embodiment calculates the ratio of manganese to iron in the lithium manganese iron phosphate battery with reference to the method provided in Embodiment 4. The difference from Embodiment 4 is that in this embodiment, when performing the DC internal resistance test, c=4%. Except for the above difference, the operation steps for calculating the ratio of manganese to iron in the lithium manganese iron phosphate battery in this embodiment are strictly consistent with those in Embodiment 4.

[0058] Example 8

[0059] This embodiment refers to the method provided in Example 6 to calculate the ratio of manganese to iron in the lithium manganese iron phosphate battery. The difference from Example 6 is that the N of the battery used in this embodiment is Mn / (N Mn +N Fe )=2. Except for the above differences, the operation steps for calculating the ratio of the content of manganese to iron in the lithium manganese iron phosphate battery in this embodiment are strictly consistent with those in Example 6.

[0060] Example 9

[0061] This embodiment refers to the method provided in Example 6 to calculate the ratio of manganese to iron in the lithium manganese iron phosphate battery. The difference from Example 6 is that the N of the battery used in this embodiment is Mn / (N Mn +N Fe )=8. Except for the above differences, the operation steps for calculating the ratio of the content of manganese to iron in the lithium manganese iron phosphate battery in this embodiment are strictly consistent with those in Example 6.

[0062] Control group

[0063] After disassembling the lithium manganese iron phosphate battery, the control group tested the Mn / Fe of the lithium manganese iron phosphate battery through conventional ICP testing. Specifically, the ICP test steps were strictly tested in accordance with the method provided by the national standard GB / T 33822-2017 "Nano lithium iron phosphate".

[0064] Test Case

[0065] 1. Test subjects

[0066] The manganese to iron ratio in the lithium manganese iron phosphate battery was calculated by the method provided in Examples 1 to 9 and the control group.

[0067] 2. Test Method

[0068] Accuracy: The manganese-iron ratio calculated in each embodiment is α, and the manganese-iron ratio measured in the control group is β. The accuracy T of each embodiment is calculated by formula (3).

[0069]

[0070] 3. Test results and analysis

[0071] The test results of this test case are shown in Table 2.

[0072] Since the precise ratio of metal elements in the positive electrode material will have a great impact on the performance of the battery, in the prior art, in order to obtain the precise ratio of metal elements in the positive electrode material, ICP is generally used for detection, which can obtain the precise element content, that is, the ratio of metal elements in the positive electrode material. ICP is a method widely recognized in the industry, so the ICP detection method is used as a control group to judge whether the method provided in this application for calculating the ratio of manganese to iron in the positive electrode of the lithium manganese iron phosphate battery is accurate.

[0073] It can be seen from Examples 1 to 5 that when the temperature in the DC internal resistance test is 45 to 60°C, there is a higher accuracy rate; and when the test temperature is 50 to 55°C, the accuracy rate can be further improved. Combining the data of Examples 4 and 6 to 7, it can be seen that in order to avoid errors caused by the position of the sudden increase point in the SOC-DCR curve not being recorded in time, the c value is preferably not higher than 5%. However, it can be seen from Example 6 that the more tested data, the better. This is because the more times the test is conducted at high temperature, the longer the time, the more severe the battery aging, which reduces the accuracy rate. Therefore, when c meets 1.5 to 2.5%, it can not only improve the accuracy of the test, but also improve the test efficiency.

[0074] Combining Example 6 and Examples 8 to 9, it can be seen that in a manganese iron phosphate lithium battery, the amount of manganese atoms and iron atoms in the positive electrode satisfies the following relationship: , can further improve the accuracy.

[0075] Table 2. Test results of this test case

[0076] plan a b Mn to Fe element ratio Accuracy Example 1 89.4％ 38.0％ 1.24 82.9％ Example 2 90.2％ 36.0％ 1.37 91.1％ Example 3 91.8％ 36.0％ 1.37 91.4％ Example 4 92.0％ 34.0％ 1.50 100.0％ Example 5 93.4％ 34.0％ 1.60 92.9％ Example 6 92.0％ 35.0％ 1.48 98.7％ Example 7 92.0％ 36.0％ 1.43 95.5％ Example 8 95.7％ 82.0％ 0.21 81.0％ Example 9 85.9％ 12.0％ 3.09 77.3％ Control group / / 1.50 /

[0077] The above embodiments are only used to illustrate the technical solution of the present application rather than to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, a person skilled in the art should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A method for calculating the manganese-iron ratio of the positive electrode in a manganese iron phosphate lithium battery, characterized in that: The method comprises the following steps: S1. Performing a first charge and discharge test on the lithium manganese iron phosphate battery to obtain a first coulombic efficiency a; S2. The lithium iron phosphate battery is then fully charged and discharged, and a DC internal resistance test is performed on the lithium iron phosphate battery during the discharge process of the lithium iron phosphate battery to obtain an SOC-DCR curve of the lithium iron phosphate battery during the discharge process, wherein the SOC value of the mutation point in the SOC-DCR curve is b; S3.N Mn It indicates the amount of manganese atoms in the positive electrode, expressed as N Fe represents the amount of iron atoms in the positive electrode, the manganese-iron ratio is calculated by the following relationship:

2. The method for calculating the positive electrode manganese-iron ratio in a lithium manganese iron phosphate battery according to claim 1, characterized in that: In S2, data collection of the SOC-DCR curve includes the following steps: S21. The lithium manganese iron phosphate battery is heated to 45-60° C., and after being left to stand for activation, the lithium manganese iron phosphate battery is subjected to cyclic charge and discharge to thereby measure the discharge capacity Q0 of the lithium manganese iron phosphate battery; S22. Subsequently, the lithium manganese iron phosphate battery is charged to make its SOC0 = 100%, and after standing for 8 to 12 seconds, the constant current discharge treatment is performed to record the discharge capacity Q1 and obtain the DCR value when SOC0 = 100%; S23. The lithium manganese iron phosphate battery is placed in a static state, and then discharged at a constant current with a cut-off capacity of c×Q0-Q1, where c is any real number between 0 and 100%; S24. After standing for 8 to 12 seconds, the lithium manganese iron phosphate battery is discharged at a constant current until the SOC value of the lithium manganese iron phosphate battery reaches SOC1 and the DCR value of the lithium manganese iron phosphate battery in this state is measured, wherein SOC1 = 100% - (c × Q0-Q1); S25. Repeat S23 and S24, and construct the SOC-DCR curve using the SOC value and the corresponding DCR value measured during each repetition of S24.

3. The method for calculating the positive electrode manganese-iron ratio in a lithium manganese iron phosphate battery according to claim 2, characterized in that: The c is not higher than 5%.

4. The method for calculating the positive electrode manganese-iron ratio in a lithium manganese iron phosphate battery according to claim 3, characterized in that: The following relationship is satisfied: 1.5%≤c≤2.5%.

5. The method for calculating the positive electrode manganese-iron ratio in a lithium manganese iron phosphate battery according to claim 2, characterized in that: In the S21, the temperature of the lithium manganese iron phosphate battery is raised to 50-55°C.

6. The method for calculating the positive electrode manganese-iron ratio in a lithium manganese iron phosphate battery according to claim 2, characterized in that: In the S21, the activation treatment is: constant current and constant voltage charging under the reaction conditions of current 0.1~1C, voltage 4.0~4.3V, and cut-off current 0.01~0.1C, and then the lithium manganese iron phosphate battery is subjected to a static treatment and constant current discharge under the reaction conditions of current 0.1~1C and cut-off voltage 2.0~3.0V.

7. The method for calculating the positive electrode manganese-iron ratio in a lithium manganese iron phosphate battery according to claim 6, characterized in that: The operation of S21 is cycled 1 to 5 times, and the last discharge capacity is Q0.

8. The method for calculating the positive electrode manganese to iron ratio in a lithium manganese iron phosphate battery according to claim 1, characterized in that: In S1, the first charge and discharge test includes the following steps: S11. The lithium manganese iron phosphate battery is charged at a constant current and constant voltage under the reaction conditions of a current of 0.05 to 0.15C, a voltage of 4.0 to 4.3V, and a cut-off current of 0.01 to 1C to obtain a charging capacity; S12. The lithium manganese iron phosphate battery is placed in a static state, and then subjected to a constant current discharge treatment under the reaction conditions of a current of 0.05 to 0.15C and a cut-off voltage of 2.0 to 3.0V to obtain a discharge capacity, and then the discharge capacity is calculated by the formula The first coulombic efficiency a is obtained.

9. The method for calculating the positive electrode manganese to iron ratio in a lithium manganese iron phosphate battery according to any one of claims 1 to 8, characterized in that: In the lithium manganese iron phosphate battery, the N Mn With the N Fe The following relationship is satisfied:

10. The method for calculating the positive electrode manganese to iron ratio in a lithium manganese iron phosphate battery according to claim 9, characterized in that: The amount of lithium atom is N Li , the amount of substance of phosphorus atom is N P In the lithium manganese iron phosphate battery, the following relationship is satisfied: 0.95≤N Li / N P ≤1.10; and / or, 0.9≤(N Mn +N Fe ) / N P ≤1.15; and / or, 1.01≤N Li / (N Mn +N Fe )≤1.10.

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