Formation process and application of lithium manganese iron phosphate battery

Abstract

The invention provides a formation process and application of a lithium manganese iron phosphate battery, and the formation process of the lithium manganese iron phosphate battery comprises the following steps: charging the lithium manganese iron phosphate battery to be formed to 2.1-2.5 V at a first constant current of 0.02-0.1 C to obtain a first intermediate product; the first intermediate product is charged to 3.6-3.8 V with a second constant current of 0.1-0.2 C, and a second intermediate product is obtained; the second intermediate product is charged to 4.1-4.3 V with a third constant current of 0.15-0.25 C, and a third intermediate product is obtained; and discharging the third intermediate product to 3.65 to 3.8 V at a constant current of 0.15 to 0.3 C. According to the formation process of the lithium iron manganese phosphate battery, the formation process of the lithium iron manganese phosphate battery is formulated by adopting a voltage cut-off mode, so that the consistency during formation can be ensured, and interface lithium precipitation purple spots caused by gas production after the battery is formed are effectively improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a formation process of a lithium manganese iron phosphate battery and its application. Background Art

[0002] Lithium manganese iron phosphate materials have recently been widely used due to their high energy density and have gradually begun to be used in the electric two-wheeled vehicle market. Compared with lithium iron phosphate materials, lithium manganese iron phosphate will produce a large amount of gas during the formation process due to the special characteristics of its dual voltage platform and system, resulting in purple spots and lithium precipitation on the initial interface, affecting the performance of the battery cell. Summary of the invention

[0003] In view of this, one purpose of the present application is to provide a formation process for a lithium iron manganese phosphate battery, and the formation process of the lithium iron manganese phosphate battery is formulated by adopting a voltage cut-off method, so as to ensure the consistency during formation, effectively improve the interface lithium purple spots caused by gas production after the lithium iron manganese phosphate battery is formed, and improve the performance of the battery cell.

[0004] Another object of the present application is to provide a lithium manganese iron phosphate battery.

[0005] To achieve the above objectives, the first aspect of the present application proposes a formation process for a lithium manganese iron phosphate battery, comprising:

[0006] The lithium manganese iron phosphate battery to be formed is charged to 2.1-2.5V at a first constant current of 0.02C-0.1C to obtain a first intermediate product;

[0007] The first intermediate product is charged to 3.6-3.8V with a second constant current of 0.1C-0.2C to obtain a second intermediate product;

[0008] The second intermediate product is charged to 4.1-4.3V with a third constant current of 0.15C-0.25C to obtain a third intermediate product;

[0009] The third intermediate product is discharged at a constant current of 0.15-0.3C to 3.65-3.8V to obtain the formed lithium manganese iron phosphate battery.

[0010] In some embodiments, the lithium manganese iron phosphate battery to be formed is charged to 2.2-2.4V at a constant current of 0.05C-0.1C.

[0011] In some embodiments, the first intermediate product is charged to 3.6-3.7V at a constant current of 0.16C-0.2C.

[0012] In some embodiments, the second intermediate product is charged to 4.1-4.3V at a constant current of 0.16C-0.2C.

[0013] In some embodiments, the third intermediate product is discharged at a constant current of 0.2-0.3C to 3.75-3.8V.

[0014] In some embodiments, the formation process of the lithium manganese iron phosphate battery is formulated based on the charge and discharge curve of the lithium manganese iron phosphate battery to be formed, the Dq / Dv curve of the first constant current charging, the Dq / Dv curves of the second constant current charging and the third constant current charging, and the Dq / Dv curve of the constant current discharge.

[0015] In some embodiments, the temperatures of the first constant current charging, the second constant current charging, the third constant current charging and the constant current discharging are all 40-50°C.

[0016] In some embodiments, the pressures of the first constant current charging, the second constant current charging, the third constant current charging, and the constant current discharging are all 480-520 KN.

[0017] In some embodiments, the formation process of the lithium manganese iron phosphate battery also includes at least one of a first placing the lithium manganese iron phosphate battery to be formed on hold before the first constant current charging, a second placing the first intermediate product on hold before the second constant current charging, a third placing the second intermediate product on hold before the third constant current charging, a fourth placing the third intermediate product on hold before the constant current discharging, and a fifth placing the third intermediate product on hold after the constant current discharging.

[0018] In some embodiments, the first holding time is 50-70 minutes.

[0019] In some embodiments, the second hold time and the third hold time are independently 50-70 seconds.

[0020] In some embodiments, the fourth holding time is 1-12 minutes.

[0021] In some embodiments, the fifth holding time is 4-6 minutes.

[0022] A second aspect of the present application provides a lithium iron phosphate battery, and a method for preparing the lithium iron phosphate battery includes the formation process of the lithium iron phosphate battery described in the present application.

[0023] The formation process of the lithium manganese iron phosphate battery described in this application can at least bring the following beneficial effects:

[0024] According to the gas production mechanism of lithium manganese iron phosphate materials during formation, as well as the characteristics of the charge and discharge curves and DQ / DV curves, a corresponding voltage cut-off formation process was developed to ensure consistency during formation, effectively improving the interface lithium purple spots caused by gas production after the formation of lithium manganese iron phosphate batteries and improving the performance of the battery cells.

[0025] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings.

[0027] in:

[0028] Figure 1 This is the charge and discharge curve of the lithium manganese iron phosphate battery to be formed.

[0029] Figure 2 This is the Dq / Dv curve of the first constant current charging.

[0030] Figure 3 Dq / Dv curves of the second constant current charging and the third constant current charging.

[0031] Figure 4 The Dq / Dv curve is formulated for constant current discharge.

[0032] Figure 5 This is a photo of the disassembly interface of the soft-pack battery after the capacity was divided in Example 1.

[0033] Figure 6 This is a photo of the disassembly interface of the soft-pack battery after the battery was divided into components according to Example 2.

[0034] Figure 7 This is a photo of the disassembly interface of the soft-pack battery after capacity division in Example 3.

[0035] Figure 8 This is a photo of the disassembly interface of the soft-pack battery after capacity division in comparative example 1.

[0036] Fig. 9 This is a photo of the disassembly interface of the soft-pack battery after capacity division in comparative example 2.

[0037] Fig.10 This is a photo of the disassembly interface of the soft-pack battery after capacity componentization in comparative example 3.

[0038] Fig.11 This is a photo of the disassembly interface of the soft-pack battery after capacity conversion in comparative example 4.

[0039] Fig.12 This is a photo of the disassembly interface of the soft-pack battery in comparative example 5 after capacity division. DETAILED DESCRIPTION

[0040] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, but cannot be understood as limiting the present application.

[0041] In this application, the disclosure of numerical ranges includes all values ​​within the entire range and the disclosure of further subdivided ranges, including the endpoints and sub-ranges given in these ranges.

[0042] In this application, the raw materials, equipment, etc. involved, unless otherwise specified, are all raw materials and equipment that can be made through commercial channels or known methods; the methods involved, unless otherwise specified, are all conventional methods.

[0043] The term "and / or", when used in a list of two or more items, means that any of the listed items can be used alone or in combination with any one or more of the listed items. For example, the expression "A and / or B" is intended to mean A or B or A and B, that is, only A, only B, or a combination of A and B.

[0044] The inventors have found that the current lithium manganese iron phosphate battery will produce a large amount of gas during formation, and a large amount of purple lithium precipitation will appear on the interface after formation, affecting the performance of the battery cell. However, it is impossible to use the conventional lithium iron phosphate formation process and overcome the above defects.

[0045] The inventor further discovered that the gas production of the lithium manganese iron phosphate battery during formation mainly includes the following parts: 1) the initial SEI film formation process; 2) the gas production through the Mn platform during the charging process; 3) the gas production through the Mn platform during the discharge process; Therefore, the lithium manganese iron phosphate battery not only needs to be charged during the initial formation process, but also needs to discharge the battery to react all the gases, thereby ensuring that the initial interface of the battery is good. Therefore, the lithium manganese iron phosphate battery has requirements for both the depth of charge and the depth of discharge during formation. Combined with the characteristics of its charge and discharge curve and DQ / DV curve, the initial charge needs to be charged to more than 4.1V, and the initial discharge needs to be discharged to the slope area between the two platforms to ensure the initial interface is good; when the conventional SOC cut-off method is used, due to the certain deviation in capacity between batches of battery cells, the depth of charge or the depth of discharge cannot reach the required position, which will lead to interface deterioration.

[0046] Therefore, the embodiments of the present application formulate a formation process of a lithium manganese iron phosphate battery using a voltage cutoff method according to the characteristics of the charge and discharge curve and the DQ / DV curve, thereby ensuring consistency during formation.

[0047] The following describes a formation process of a lithium manganese iron phosphate battery according to an embodiment of the present application with reference to the accompanying drawings.

[0048] The formation process of the lithium manganese iron phosphate battery of the embodiment of the present application includes the following steps:

[0049] S101, charging the lithium manganese iron phosphate battery to be formed with a first constant current of 0.02C-0.1C to 2.1-2.5V (ie, a cut-off voltage of 2.1-2.5V) to obtain a first intermediate product.

[0050] Exemplarily, the current of the first constant current charging includes but is not limited to 0.03C, 0.04C, 0.05C, 0.06C, 0.07C, 0.08C, 0.09C or 1C, etc.

[0051] In the embodiment of the present application, the current of the first constant current charging is within the above range, which can ensure the full output of gas during initial film formation and ensure a good film forming effect; if it is lower than 0.02C, the production efficiency is low; if it is higher than 0.1C, the film forming effect is poor.

[0052] Exemplarily, the cut-off voltage of the first constant current charging includes but is not limited to 2.1V, 2.2V, 2.3V, 2.4V or 2.5V, etc.

[0053] In the embodiment of the present application, the cut-off voltage of the first constant current charging is within the above range, which can ensure the integrity of the SEI film; if it is lower than 2.1V, the SEI film is incomplete, affecting the performance; if it is higher than 2.5V, it causes a waste of formation efficiency.

[0054] As an optional example, the lithium manganese iron phosphate battery to be formed is charged to 2.2-2.4V at a constant current of 0.05C-0.1C to obtain a first intermediate product.

[0055] In some embodiments, the formation process of the lithium manganese iron phosphate battery further includes a step of first placing the lithium manganese iron phosphate battery to be formed before the first constant current charging.

[0056] In some embodiments, the first holding time is 50-70 min, including but not limited to 55 min, 60 min, 65 min or 70 min, etc.

[0057] S102, charging the first intermediate product with a second constant current of 0.1C-0.2C to 3.6-3.8V (ie, a cut-off voltage of 3.6-3.8V) to obtain a second intermediate product.

[0058] Exemplarily, the current of the second constant current charging includes but is not limited to 0.1C, 0.11C, 0.12C, 0.13C, 0.14C, 0.15C, 0.16C, 0.17C, 0.18C or 0.2C, etc.

[0059] In the embodiment of the present application, the current of the second constant current charging is within the above range, which can fully output the initial gas, complete the formation of SEI, and improve the performance of the battery cell; if it is lower than 0.1C, the efficiency is low; if it is higher than 0.2C, the performance will deteriorate.

[0060] Exemplarily, the cut-off voltage of the second constant current charging includes but is not limited to 3.6V, 3.65V, 3.7V, 3.75V or 3.8V, etc.

[0061] In the embodiment of the present application, the cut-off voltage of the second constant current charging is within the above range, which can ensure the integrity of the second reaction peak and improve the performance of the battery cell; if it is lower than 3.6V, the reaction is not fully completed, affecting the performance; if it is higher than 3.8V, the efficiency is low.

[0062] As an optional example, the first intermediate product is charged to 3.6-3.7V at a constant current of 0.16C-0.2C to obtain a first intermediate product.

[0063] In some embodiments, the formation process of the lithium manganese iron phosphate battery further includes a step of performing a second shelving of the first intermediate product before the second constant current charging.

[0064] In some embodiments, the second holding time is 50-70 seconds, including but not limited to 55 seconds, 60 seconds, 65 seconds or 70 seconds.

[0065] S103, charging the second intermediate product with a third constant current of 0.15C-0.25C to 4.1-4.3V (ie, a cut-off voltage of 4.1-4.3V), to obtain a third intermediate product.

[0066] Exemplarily, the current of the third constant current charging includes but is not limited to 0.16C, 0.17C, 0.18C, 0.19C, 0.20C, 0.21C, 0.22C, 0.23C, 0.24C or 0.25C, etc.

[0067] In the embodiment of the present application, the current of the third constant current charging is within the above range, which can ensure a good interface; if it is lower than 0.15C, the efficiency is low; if it is higher than 0.25C, the reaction is violent and the interface deteriorates.

[0068] Exemplarily, the cut-off voltage of the third constant current charging includes but is not limited to 4.1V, 4.15V, 4.2V, 4.25V or 4.3V, etc.

[0069] In the embodiment of the present application, the cut-off voltage of the third constant current charging is within the above range, which can ensure that all gas is produced; if it is lower than 4.1V, the gas cannot be completely produced, affecting the interface; if it is higher than 4.3V, it exceeds the upper limit voltage and deteriorates the performance.

[0070] As an optional example, the second intermediate product is charged to 4.1-4.3V at a constant current of 0.16C-0.2C to obtain a third intermediate product.

[0071] In some embodiments, the formation process of the lithium manganese iron phosphate battery further includes a step of subjecting the second intermediate product to a third shelving step before the third constant current charging.

[0072] In some embodiments, the third holding time is 50-70 seconds, including but not limited to 55 seconds, 60 seconds, 65 seconds or 70 seconds.

[0073] S104, discharging the third intermediate product at a constant current of 0.15-0.3C to 3.65-3.8V (ie, a cut-off voltage of 3.65-3.8V) to obtain the formed lithium manganese iron phosphate battery.

[0074] Exemplarily, the constant current discharge current includes but is not limited to 0.16C, 0.18C, 0.20C, 0.22C, 0.24C, 0.26C, 0.28C or 0.3C, etc.

[0075] In the embodiments of the present application, the constant current discharge current is within the above range, which can ensure production efficiency and a good interface; if it is lower than 0.15C, the efficiency is low; if it is higher than 0.3C, gas production is severe and the interface deteriorates.

[0076] Exemplarily, the cut-off voltage of the constant current discharge includes but is not limited to 3.7V, 3.75V or 3.8V, etc. In the embodiment of the present application, the cut-off voltage of the constant current discharge is between the iron voltage platform (about 3.3V) and the manganese voltage platform (about 3.9V).

[0077] In the embodiments of the present application, the cut-off voltage of the constant current discharge is within the above range, which can ensure a good interface after aging; if it is lower than 3.65V, the interface deteriorates; if it is higher than 3.8V, the interface deteriorates and the performance is poor.

[0078] As an optional example, the third intermediate product is discharged to 3.75-3.8V at a constant current of 0.2-0.3C.

[0079] In some embodiments, the formation process of the lithium manganese iron phosphate battery further includes a step of performing a fourth shelving on the third intermediate product before the constant current discharge.

[0080] In some embodiments, the fourth holding time is 1-12 min, including but not limited to 2 min, 4 min, 6 min, 9 min, 10 min, 11 min or 12 min, etc.

[0081] In some embodiments, the formation process of the lithium manganese iron phosphate battery further includes a fifth rest step after the constant current discharge.

[0082] In some embodiments, the fifth holding time is 4-6 minutes, including but not limited to 4.5 minutes, 5 minutes, 5.5 minutes or 6 minutes.

[0083] In some embodiments, the formation process of the lithium manganese iron phosphate battery is based on the charge and discharge curve of the lithium manganese iron phosphate battery to be formed (such as Figure 1 As shown), the Dq / Dv curve of the first constant current charge (as shown Figure 2 As shown, that is, the first charging DQ / DV curve), the second constant current charging and the third constant current charging DQ / Dv curve (as shown Figure 3 As shown, that is, the second and third charging DQ / DV curves) and the constant current discharge Dq / Dv curve (as shown Figure 4 As shown, that is, the fourth discharge DQ / DV curve) is formulated.

[0084] In some embodiments, the temperature of the first constant current charging, the second constant current charging, the third constant current charging and the constant current discharging are all 40-50°C, including but not limited to 42°C, 45°C, 47°C or 29°C, etc.

[0085] It should be noted that, in the embodiment of the present application, although the temperatures of the first constant current charging, the second constant current charging, the third constant current charging and the constant current discharging are within the above range, they can be the same or different.

[0086] In some embodiments, the pressures of the first constant current charging, the second constant current charging, the third constant current charging and the constant current discharging are all 480-520 KN, including but not limited to 485 KN, 490 KN, 495 KN, 500 KN, 505 KN, 510 KN or 515 KN, etc.

[0087] It should be noted that, in the embodiment of the present application, although the pressures of the first constant current charging, the second constant current charging, the third constant current charging and the constant current discharging are within the above range, they can be the same or different.

[0088] The formation process of the lithium manganese iron phosphate battery in the embodiment of the present application formulates a corresponding voltage cutoff formation process according to the gas production mechanism of the lithium manganese iron phosphate material during formation and the characteristics of the charge and discharge curve and the DQ / DV curve, thereby ensuring consistency during formation, effectively improving the interface lithium purple spots caused by gas production after the lithium manganese iron phosphate battery is formed, and improving the performance of the battery cell.

[0089] The formation process of the lithium manganese iron phosphate battery of the embodiment of the present application can be widely used in the preparation of lithium manganese iron phosphate batteries.

[0090] The preparation method of the lithium iron phosphate battery of the embodiment of the present application includes the formation process of the lithium iron phosphate battery described in the present application.

[0091] Certain features of the present technology are further illustrated in the following non-limiting examples.

[0092] 1. Examples and Comparative Examples

[0093] The lithium manganese iron phosphate batteries to be formed in the following embodiments and comparative examples are all soft-pack batteries. The preparation method of the soft-pack batteries comprises the following steps:

[0094] (1) Preparation of positive electrode: Lithium iron manganese phosphate material (LiMn 0.6 Fe 0.4 PO4), polyvinylidene fluoride (PVDF), conductive carbon black (SP), and single-walled carbon nanotubes (CNT) were dissolved in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 95.5:2.0:2.0:0.5, stirred evenly, and evenly coated on a 13 μm carbon-coated aluminum foil to obtain a surface density of 360 g / m 2 The positive electrode.

[0095] (2) Preparation of negative electrode sheet: Artificial graphite, conductive carbon black (SP), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed uniformly in a mass ratio of 96.0:0.8:1.4:1.8, and evenly coated on a 6 μm copper foil to obtain a surface density of 160 g / m 2 The negative electrode.

[0096] (3) Preparation of electrolyte: Lithium hexafluorophosphate (LiPF6) is dispersed in a solvent to obtain a 1 mol / L electrolyte; wherein the solvent is a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1.

[0097] (4) Selection of diaphragm: The diaphragm is a polyethylene ceramic diaphragm with a thickness of 11 μm.

[0098] (5) Assembly: The positive electrode sheet, separator, and negative electrode sheet are stacked, assembled, injected, and left to stand at high temperature to obtain a soft-pack battery with a capacity of 2.5 Ah.

[0099] Example 1

[0100] The formation process of the lithium manganese iron phosphate battery of this embodiment includes: placing the lithium manganese iron phosphate battery to be formed on a formation cabinet at 45° C. and applying a force of 500KN; and then performing the formation in the following steps:

[0101] ① Leave for 1 hour;

[0102] ② Charge to 2.3V at a constant current of 0.1C;

[0103] ③ Leave for 1 minute;

[0104] ④ Charge to 3.65V at a constant current of 0.16C;

[0105] ⑤ Leave for 1 minute;

[0106] ⑥ Charge to 4.1V at a constant current of 0.2C;

[0107] ⑦ Leave for 10 minutes;

[0108] ⑧Discharge at a constant current of 0.2C to 3.75V;

[0109] ⑨Set aside for 5 minutes.

[0110] Example 2

[0111] The formation process of the lithium manganese iron phosphate battery of this embodiment includes: placing the lithium manganese iron phosphate battery to be formed on a formation cabinet at 45° C. and applying a force of 480 KN; and then performing the formation in the following steps:

[0112] ① Leave for 1 hour;

[0113] ② Charge to 2.3V at a constant current of 0.1C;

[0114] ③ Leave for 1 minute;

[0115] ④ Charge to 3.7V at a constant current of 0.16C;

[0116] ⑤ Leave for 1 minute;

[0117] ⑥ Charge to 4.3V at a constant current of 0.16C;

[0118] ⑦ Set aside for 1 minute;

[0119] ⑧Discharge at a constant current of 0.2C to 3.8V;

[0120] ⑨Set aside for 5 minutes.

[0121] Example 3

[0122] The formation process of the lithium manganese iron phosphate battery of this embodiment includes: placing the lithium manganese iron phosphate battery to be formed on a formation cabinet at 45° C. and applying a force of 500KN; and then performing the formation in the following steps:

[0123] ① Leave for 1 hour;

[0124] ② Charge to 2.1V at a constant current of 0.02C;

[0125] ③ Leave for 1 minute;

[0126] ④ Charge to 3.6V at a constant current of 0.1C;

[0127] ⑤ Leave for 1 minute;

[0128] ⑥ Charge to 4.1V at a constant current of 0.15C;

[0129] ⑦ Leave for 10 minutes;

[0130] ⑧Discharge at a constant current of 0.15C to 3.65V;

[0131] ⑨Set aside for 5 minutes.

[0132] Example 4 (Charging current and cut-off voltage are both upper limits)

[0133] The formation process of the lithium manganese iron phosphate battery of this embodiment includes: placing the lithium manganese iron phosphate battery to be formed on a formation cabinet at 45° C. and applying a force of 500KN; and then performing the formation in the following steps:

[0134] ① Leave for 1 hour;

[0135] ② Charge to 2.5V at a constant current of 0.1C;

[0136] ③ Leave for 1 minute;

[0137] ④ Charge to 3.8V at a constant current of 0.2C;

[0138] ⑤ Leave for 1 minute;

[0139] ⑥ Charge to 4.3V at a constant current of 0.25C;

[0140] ⑦ Leave for 10 minutes;

[0141] ⑧Discharge at a constant current of 0.3C to 3.8V;

[0142] ⑨Set aside for 5 minutes.

[0143] Example 5 (Compared with Example 1, without shelving)

[0144] The formation process of the lithium manganese iron phosphate battery of this embodiment includes: placing the lithium manganese iron phosphate battery to be formed on a formation cabinet at 45° C. and applying a force of 500KN; and then performing the formation in the following steps:

[0145] ① Charge to 2.3V with a constant current of 0.1C;

[0146] ② Charge to 3.65V at a constant current of 0.16C;

[0147] ③ Charge to 4.1V at a constant current of 0.2C;

[0148] ④ Leave for 10 minutes;

[0149] ⑤Discharge at a constant current of 0.2C to 3.75V.

[0150] Comparative Example 1 (Full Charge - No Constant Current Discharge)

[0151] The formation process of the lithium manganese iron phosphate battery of this comparative example comprises: placing the lithium manganese iron phosphate battery to be formed on a formation cabinet at 45° C., applying a force of 500KN; and then performing the formation in the following steps:

[0152] ① Leave for 1 hour;

[0153] ② Charge to 2.3V at a constant current of 0.1C;

[0154] ③ Leave for 1 minute;

[0155] ④ Charge to 3.65V at a constant current of 0.16C;

[0156] ⑤ Leave for 1 minute;

[0157] ⑥ Charge to 4.1V at a constant current of 0.2C;

[0158] ⑦ Set aside for 5 minutes.

[0159] Comparative Example 2 (Discharge to Mn platform - constant current discharge cut-off voltage exceeds the upper limit of this application)

[0160] The formation process of the lithium manganese iron phosphate battery of this comparative example comprises: placing the lithium manganese iron phosphate battery to be formed on a formation cabinet at 45° C., applying a force of 500KN; and then performing the formation in the following steps:

[0161] ① Leave for 1 hour;

[0162] ② Charge to 2.3V at a constant current of 0.1C;

[0163] ③ Leave for 1 minute;

[0164] ④ Charge to 3.65V at a constant current of 0.16C;

[0165] ⑤ Leave for 1 minute;

[0166] ⑥ Charge to 4.1V at a constant current of 0.2C;

[0167] ⑦ Set aside for 5 minutes;

[0168] ⑧Discharge at a constant current of 0.2C to 3.85V;

[0169] ⑨Set aside for 5 minutes.

[0170] Comparative Example 3 (discharge to Fe platform - constant current discharge cut-off voltage is lower than the lower limit of this application)

[0171] The formation process of the lithium manganese iron phosphate battery of this comparative example comprises: placing the lithium manganese iron phosphate battery to be formed on a formation cabinet at 45° C., applying a force of 500KN; and then performing the formation in the following steps:

[0172] ① Leave for 1 hour;

[0173] ② Charge to 2.3V at a constant current of 0.1C;

[0174] ③ Leave for 1 minute;

[0175] ④ Charge to 3.65V at a constant current of 0.16C;

[0176] ⑤ Leave for 1 minute;

[0177] ⑥ Charge to 4.1V at a constant current of 0.2C;

[0178] ⑦ Set aside for 5 minutes;

[0179] ⑧Discharge at a constant current of 0.2C to 3.3V;

[0180] ⑨Set aside for 5 minutes.

[0181] Comparative Example 4 (discharge to low SOC-constant current discharge cut-off voltage is lower than the lower limit of this application)

[0182] The formation process of the lithium manganese iron phosphate battery of this comparative example comprises: placing the lithium manganese iron phosphate battery to be formed on a formation cabinet at 45° C., applying a force of 500KN; and then performing the formation in the following steps:

[0183] ① Leave for 1 hour;

[0184] ② Charge to 2.3V at a constant current of 0.1C;

[0185] ③ Leave for 1 minute;

[0186] ④ Charge to 3.65V at a constant current of 0.16C;

[0187] ⑤ Leave for 1 minute;

[0188] ⑥ Charge to 4.1V at a constant current of 0.2C;

[0189] ⑦ Set aside for 5 minutes;

[0190] ⑧Discharge at a constant current of 0.2C to 3.0V;

[0191] ⑨Set aside for 5 minutes.

[0192] Comparative Example 5 (Charging to Mn platform - the third constant current charging cut-off voltage is lower than the lower limit of this application)

[0193] The formation process of the lithium manganese iron phosphate battery of this comparative example comprises: placing the lithium manganese iron phosphate battery to be formed on a formation cabinet at 45° C., applying a force of 500KN; and then performing the formation in the following steps:

[0194] ① Leave for 1 hour;

[0195] ② Charge to 2.3V at a constant current of 0.1C;

[0196] ③ Leave for 1 minute;

[0197] ④ Charge to 3.65V at a constant current of 0.16C;

[0198] ⑤ Leave for 1 minute;

[0199] ⑥ Charge to 3.9V at a constant current of 0.2C;

[0200] ⑦ Set aside for 5 minutes;

[0201] ⑧Discharge at a constant current of 0.2C to 3.75V;

[0202] ⑨Set aside for 5 minutes.

[0203] 2. Performance Test

[0204] The lithium manganese iron phosphate batteries formed in each embodiment or comparative example were left at a high temperature of 45° C. for 48 hours, and then divided into different capacities. The divided soft-pack batteries were charged to 4.3 V at a constant current of 0.5 C, and then disassembled to observe the negative electrode interface.

[0205] The method of dividing the capacity comprises the following steps:

[0206] ① Leave for 10 minutes;

[0207] ② Charge to 4.3V at a constant current and constant voltage of 0.33C;

[0208] ③ Leave for 10 minutes;

[0209] ④Discharge to 2.5V at a constant current of 0.33C;

[0210] ⑤ Leave for 10 minutes;

[0211] ⑥ Follow the above steps ①-⑤ for 2 cycles to obtain the soft-pack battery after capacity division.

[0212] The disassembly interface results of the soft-pack batteries after capacity division in some embodiments and comparative examples are shown in Table 1.

[0213] Table 1: Disassembly interface results of soft-pack batteries after capacity division in some embodiments and comparative examples

[0214]

[0215]

[0216] From the disassembly results in Table 1, it can be seen that comparative examples 1-5 all showed purple spots of lithium precipitation to varying degrees, while examples 1-3 had good interfaces after volume separation, indicating that all the gas was produced during the formation and did not affect the interface.

[0217] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0218] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0219] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A formation process for a lithium manganese iron phosphate battery, characterized in that: include: The lithium manganese iron phosphate battery to be formed is charged to 2.1-2.5V at a first constant current of 0.02C-0.1C to obtain a first intermediate product; The first intermediate product is charged to 3.6-3.8V with a second constant current of 0.1C-0.2C to obtain a second intermediate product; The second intermediate product is charged to 4.1-4.3V with a third constant current of 0.15C-0.25C to obtain a third intermediate product; The third intermediate product is discharged at a constant current of 0.15-0.3C to 3.65-3.8V to obtain the formed lithium manganese iron phosphate battery.

2. The chemical formation process according to claim 1, characterized in that: The lithium manganese iron phosphate battery to be formed is charged to 2.2-2.4V at a constant current of 0.05C-0.1C.

3. The chemical formation process according to claim 1, characterized in that: The first intermediate product is charged to 3.6-3.7V at a constant current of 0.16C-0.2C.

4. The chemical formation process according to claim 1, characterized in that: The second intermediate product is charged to 4.1-4.3V at a constant current of 0.16C-0.2C; and / or, The third intermediate product is discharged at a constant current of 0.2-0.3C to 3.75-3.8V.

5. The chemical formation process according to any one of claims 1 to 4, characterized in that: The formation process of the lithium manganese iron phosphate battery is formulated based on the charge and discharge curve of the lithium manganese iron phosphate battery to be formed, the Dq / Dv curve of the first constant current charging, the Dq / Dv curves of the second constant current charging and the third constant current charging, and the Dq / Dv curve of the constant current discharge.

6. The chemical formation process according to any one of claims 1 to 4, characterized in that: The temperatures of the first constant current charging, the second constant current charging, the third constant current charging and the constant current discharging are all 40-50°C.

7. The chemical formation process according to any one of claims 1 to 4, characterized in that: The pressures of the first constant current charging, the second constant current charging, the third constant current charging and the constant current discharging are all 480-520KN.

8. The chemical formation process according to any one of claims 1 to 4, characterized in that: The formation process of the lithium manganese iron phosphate battery also includes at least one of the following steps: placing the lithium manganese iron phosphate battery to be formed in a first placing step before the first constant current charging, placing the first intermediate product in a second placing step before the second constant current charging, placing the second intermediate product in a third placing step before the third constant current charging, placing the third intermediate product in a fourth placing step before the constant current discharging, and placing the third intermediate product in a fifth placing step after the constant current discharging.

9. The chemical formation process according to claim 8, characterized in that: The first holding time is 50-70 minutes; and / or, The second hold time and the third hold time are independently 50-70 seconds; and / or, The fourth holding time is 1-12 minutes; and / or, The fifth holding time is 4-6 minutes.

10. A lithium manganese iron phosphate battery, characterized in that: The method for preparing the lithium iron phosphate battery comprises the formation process as described in any one of claims 1 to 9.

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