Lithium iron phosphate battery and formation method and preparation method thereof
By using 2-5C ratio pulse method in lithium iron phosphate batteries, the inorganic lithium salt composition of the SEI film is adjusted to form a denser film, which solves the battery attenuation problem in high temperature environments and significantly improves the stability of the battery at high temperatures.
Patent Information
- Application Number
- CN202411734482.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-29
- Publication Date
- 2025-02-28
AI Technical Summary
Lithium iron phosphate batteries decay too fast in the early cycle in a high-temperature environment, resulting in a degradation of battery performance.
The 2-5C ratio pulse method is used to make the inorganic lithium salt components in the SEI film to form a denser film on the graphite surface.
The stability of the SEI film is significantly improved under high temperature environments, effectively solving the high temperature attenuation problem of lithium iron phosphate batteries.
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Figure CN119542587A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of lithium iron phosphate batteries, and in particular to a lithium iron phosphate battery and a formation method and a preparation method thereof. Background Art
[0002] Lithium iron phosphate (LFP) / graphite batteries are accelerating to become the main force of electrochemical energy storage, because LFP itself has the advantages of long cycle, high safety, low cost, etc. At present, through technical modification, the performance of LFP is gradually improving, and its proportion in power batteries is also increasing year by year. However, due to its structural influence, LFP has always been a problem that needs to be solved for its rapid decay in the early stage of the cycle, especially in high temperature environments.
[0003] Currently, the focus of improving the high-temperature performance of LFP / graphite batteries is on the negative electrode graphite and electrolyte system. The positive electrode is modified to inhibit the dissolution of iron ions. The main strategy for graphite is to use single particles with uniform particle size and multiple de-fine powder processes. The electrolyte is mainly based on high-temperature stable film-forming additives.
[0004] The high-temperature performance of LFP / graphite batteries can be improved by optimizing LFP modification, graphite and electrolyte, but this will bring the risk of increased costs. Under high-temperature environment, the stability of the SEI film is the key to its high-temperature performance. Under high-temperature environment, the overall dynamics of the battery are improved, the chemical activity is increased, and the structure of graphite changes more dramatically than at room temperature. In comparison, for the same number of cycles, the expansion of the graphite pole piece under high-temperature environment is 5-10% higher than that under normal temperature environment.
[0005] Therefore, preventing lithium iron phosphate batteries from decaying too quickly in high temperature environments is a technical problem that needs to be solved urgently in this field. Summary of the invention
[0006] The invention provides a lithium iron phosphate battery and a formation method and a preparation method thereof.
[0007] In order to solve the above technical problems, the present invention provides a formation method of a lithium iron phosphate battery, comprising the following steps: step S1, charging the lithium iron phosphate battery to be formed at a constant current rate of 0.05-0.2C and letting it stand; step S2, performing 10-60 cycles as follows: charging the lithium iron phosphate battery after standing at a constant current rate of 2-5C for 5-10s, and letting it stand; step S3, finally charging at a constant current rate of 0.1-0.3C and letting it stand.
[0008] Furthermore, in the step S1, the lithium iron phosphate battery to be formed is charged at a constant current rate of 0.08-0.12C.
[0009] Furthermore, in step S1, the charging capacity of the lithium iron phosphate battery at this stage is 10-15% SOC.
[0010] Furthermore, in step S2, the total charge capacity of the lithium iron phosphate battery at this stage is 10-30% SOC.
[0011] Furthermore, in step S3, constant current charging is performed at a rate of 0.1-0.15C.
[0012] Furthermore, in step S3, the total charge capacity of the lithium iron phosphate battery at this stage is 10-35% SOC.
[0013] On the other hand, the present invention also provides a method for preparing a lithium iron phosphate battery, comprising: winding the positive and negative electrode sheets into a battery core, coating them with an insulating coating film, placing them in a square aluminum shell, and baking, injecting liquid, forming, and measuring the capacity to form a lithium iron phosphate battery; wherein the formation method of the lithium iron phosphate battery described above is used for the formation.
[0014] Furthermore, the method for preparing the positive electrode sheet comprises: stirring, coating, cold pressing and slitting lithium iron phosphate, a conductive agent and a first binder in sequence to form a positive electrode sheet required for winding.
[0015] Furthermore, the conductive agent includes SP.
[0016] Furthermore, the first binder includes PVDF.
[0017] Furthermore, the method for preparing the negative electrode sheet comprises: stirring, coating, cold pressing and slitting artificial graphite, a conductive agent and a second binder in sequence to form a negative electrode sheet required for winding.
[0018] Furthermore, the second binder includes any one of CMC and SBR or a combination of both.
[0019] In a third aspect, the present invention further provides a lithium iron phosphate battery, which is manufactured using the lithium iron phosphate battery manufacturing method as described above.
[0020] The beneficial effect of the present invention is that the lithium iron phosphate battery and its formation method and preparation method of the present invention, on the basis of not changing the existing chemical system of the existing battery, are formed by a 2-5C rate pulse mode, and the inorganic lithium salt component in the SEI film is adjusted to form a denser film on the graphite surface. The stability of the SEI film is slightly improved at room temperature, but the stability can be greatly improved in a high temperature environment, which effectively solves the high temperature attenuation problem of the current lithium iron phosphate battery.
[0021] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention are realized and obtained by the structures particularly pointed out in the description and the drawings.
[0022] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0024] Figure 1 A process flow chart of a lithium iron phosphate battery formation method according to some embodiments is shown. DETAILED DESCRIPTION
[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0026] like Figure 1 As shown, at least one embodiment provides a formation method of a lithium iron phosphate battery, comprising the following steps: step S1, charging the lithium iron phosphate battery to be formed at a constant current rate of 0.05-0.2C, and letting it stand; step S2, performing 10-60 cycles according to the following steps: charging the lithium iron phosphate battery after standing at a constant current rate of 2-5C for 5-10s, and letting it stand; step S3, finally charging at a constant current rate of 0.1-0.3C, and letting it stand.
[0027] At least one embodiment provides a method for preparing a lithium iron phosphate battery, comprising: winding the positive and negative electrode sheets into a battery cell, coating them with an insulating coating film, placing them in a square aluminum shell, baking, injecting liquid, forming, and measuring the capacity to form a lithium iron phosphate battery; wherein the formation method of the lithium iron phosphate battery described above is used for the formation.
[0028] Specifically, the total charge amount of the lithium iron phosphate battery in the formation process is 48-53% SOC, and the remaining charge amount is completed to full charge in the capacity process; wherein, SOC refers to the charging rate of the battery, such as 0.1C constant current charging for 60 minutes means 10% SOC, and 100% SOC represents full charge.
[0029] Some embodiments further provide a lithium iron phosphate battery, which is manufactured using the lithium iron phosphate battery manufacturing method as described above.
[0030] Among them, lithium iron phosphate, conductive agent SP, and binder PVDF are mixed in a certain proportion and sequentially subjected to processes such as stirring, coating, cold pressing, and slitting to form the positive electrode sheet required for winding; artificial graphite, conductive agent SP, and binder (CMC / SBR) are mixed in a certain proportion and sequentially subjected to processes such as stirring, coating, cold pressing, and slitting to form the negative electrode sheet required for winding; the positive and negative electrode sheets are wound into a winding core, which is coated with an insulating coating film and placed in a square aluminum shell, and then made into a battery cell after processes such as baking, liquid injection, formation, and capacity.
[0031] Wherein, the conductive agent SP is conductive carbon black, the binder PVDF is polyvinylidene fluoride, the binder CMC is carboxymethyl cellulose, and the SBR is polystyrene butadiene copolymer.
[0032] Comparative Example 1:
[0033] Lithium iron phosphate, conductive agent SP, and binder PVDF are made into the positive electrode sheet required for winding through the processes of stirring, coating, cold pressing, and slitting; artificial graphite, conductive agent SP, and binder (CMC / SBR) are made into the negative electrode sheet required for winding through the processes of stirring, coating, cold pressing, and slitting; the positive and negative electrode sheets are made into battery cells by winding, the battery cells are coated with insulating coating films, placed in square aluminum shells, and then baked, injected, formed, and capacitated to make lithium iron phosphate batteries.
[0034] The formation method of this embodiment is as follows: first charge with a constant current of 0.1C for 60 minutes, then let it stand for 30 minutes, then charge with a constant current of 0.1C for 240 minutes, then let it stand for 5 minutes, and the formation is completed.
[0035] Embodiment 1:
[0036] In this embodiment, a battery cell is prepared by the method described in Comparative Example 1, except for the formation method.
[0037] The formation method of the present embodiment is as follows:
[0038] 1) First charge at 0.1C constant current for 60 minutes, then let stand for 30 minutes, the charge capacity is 10% SOC;
[0039] 2) Then, 18 cycles were performed as follows: charging at 2C constant current for 10 seconds, and then resting for 10 minutes; a total pulse charge of 10% SOC;
[0040] 3) Finally, the battery was charged at a constant current rate of 0.1C for 180 minutes, and then left to stand for 5 minutes. The charge capacity was 30% SOC, and the formation was completed.
[0041] Embodiment 2:
[0042] In this embodiment, a battery cell is prepared by the method described in Comparative Example 1, except for the formation method.
[0043] The formation method of the present embodiment is as follows:
[0044] 1) First charge at 0.1C constant current for 60 minutes, then let stand for 30 minutes, the charge capacity is 10% SOC;
[0045] 2) Then, 36 cycles were performed as follows: charging at 2C constant current for 10 seconds, and then resting for 10 minutes; a total pulse charging of 20% SOC;
[0046] 3) Finally, the battery was charged at a constant current rate of 0.1C for 120 minutes, and then left to stand for 5 minutes. The charge capacity was 20% SOC, and the formation was completed.
[0047] Embodiment 3:
[0048] This embodiment adopts the method described in Comparative Example 1 to prepare a battery cell, the difference being the formation method. The formation method of this embodiment is as follows:
[0049] 1) First charge at 0.1C constant current for 60 minutes, then let stand for 30 minutes, the charge capacity is 10% SOC;
[0050] 2) Then, 54 cycles were performed as follows: charging at 2C constant current for 10 seconds, followed by 10 minutes of rest; a total pulse charge of 30% SOC;
[0051] 3) Finally, the battery was charged at a constant current rate of 0.1C for 120 minutes, and then left to stand for 5 minutes. The charge capacity was 20% SOC, and the formation was completed.
[0052] Embodiment 4:
[0053] In this embodiment, a battery cell is prepared by the method described in Comparative Example 1, except for the formation method.
[0054] The formation method of the present embodiment is as follows:
[0055] 1) First charge at 0.1C constant current for 60 minutes, then let stand for 30 minutes, the charge capacity is 10% SOC;
[0056] 2) Then, 14 cycles were performed as follows: charging at 5C constant current for 10 seconds, followed by resting for 10 minutes; a total pulse charge of 19.44% SOC;
[0057] 3) Finally, the battery was charged at a constant current rate of 0.1C for 115 minutes, and then left to stand for 5 minutes. The charge capacity was 19.17% SOC, and the formation was completed.
[0058] Embodiment 5:
[0059] In this embodiment, a battery cell is prepared by the method described in Comparative Example 1, except for the formation method.
[0060] The formation method of the present embodiment is as follows:
[0061] 1) First charge at 0.1C constant current for 60 minutes, then let stand for 30 minutes, the charge capacity is 10% SOC;
[0062] 2) Then, 15 cycles were performed as follows: charging at 5C constant current for 5 seconds, and then resting for 10 minutes; a total pulse charging of 10.41% SOC;
[0063] 3) Finally, the battery was charged at a constant current rate of 0.1C for 178 minutes, and then left to stand for 5 minutes. The charge capacity was 29.67% SOC, and the formation was completed.
[0064] Embodiment 6:
[0065] In this embodiment, a battery cell is prepared by the method described in Comparative Example 1, except for the formation method.
[0066] The formation method of the present embodiment is as follows:
[0067] 1) First charge at 0.1C constant current for 60 minutes, then let stand for 30 minutes, the charge capacity is 10% SOC;
[0068] 2) Then, 29 cycles were performed as follows: charging at 5C constant current for 5 seconds, and then resting for 10 minutes; a total pulse charging of 20.14% SOC;
[0069] 3) Finally, the battery was charged at a constant current rate of 0.1C for 120 minutes, and then left to stand for 5 minutes. The charge capacity was 20% SOC, and the formation was completed.
[0070] Embodiment 7:
[0071] In this embodiment, a battery cell is prepared by the method described in Comparative Example 1, except for the formation method.
[0072] The formation method of the present embodiment is as follows:
[0073] 1) First charge at 0.1C constant current for 60 minutes, then let stand for 30 minutes, the charge capacity is 10% SOC;
[0074] 2) Then, the battery was cycled 43 times as follows: charging at 5C constant current for 5 seconds, followed by resting for 10 minutes; the total SOC was 29.86%;
[0075] 3) Finally, the battery was charged at a constant current rate of 0.1C for 60 minutes, and then left to stand for 5 minutes. The charge capacity reached 10% SOC, and the formation was completed.
[0076] The lithium iron phosphate batteries prepared in Comparative Example 1 and Examples 1-7 were cycled for 500 cycles at 0.5C at 25°C and 55°C, respectively. The capacity retention rate data are shown in Table 1 below.
[0077] Table 1 Capacity retention rate of lithium iron phosphate batteries prepared in comparative example 1 and examples 1-8
[0078]
[0079]
[0080] Table 1 shows the capacity retention rates after 500 cycles at 25°C 0.5C and 55°C 0.5C respectively through different formation processes. Compared with Comparative Example 1, the other processes all adopt 2-5C rate pulse charging, which has a slight improvement at room temperature, and the capacity retention rate is significantly improved at high temperature, indicating that the stability of the SEI film can be improved by using this rate pulse charging; the data of Examples 1, 2, 3 and Examples 5, 6, 7 show that when different rate pulse charging is used, when the pulse charging SOC is 20%, its high temperature performance is optimal, indicating that the SEI film formed under this process is the most stable; the comparative data of Examples 1, 4, 5 show that too long 2-5C rate pulse charging time may have a counter-effect on the stability of its film formation, and the corresponding time needs to be adjusted when using different rate pulse charging.
[0081] In summary, the lithium iron phosphate battery and its formation method and preparation method of the present invention, without changing the existing chemical system of the existing battery, are formed by a 2-5C rate pulse method, and the inorganic lithium salt component in the SEI film is adjusted to form a denser film on the graphite surface. The stability of the SEI film is slightly improved at room temperature, but the stability can be greatly improved in a high temperature environment, effectively solving the high temperature attenuation problem of the current lithium iron phosphate battery.
[0082] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.
Claims
1. A formation method for a lithium iron phosphate battery, characterized in that: The steps include: Step S1, charging the lithium iron phosphate battery to be formed at a constant current rate of 0.05-0.2C and leaving it to stand; Step S2, performing 10-60 cycles as follows: charging the lithium iron phosphate battery after standing at a constant current of 2-5C for 5-10s, and standing at a constant current of 2-5C; Step S3, finally charging at a constant current rate of 0.1-0.3C and letting it stand.
2. The chemical formation method according to claim 1, characterized in that In the step S1, the lithium iron phosphate battery to be formed is charged at a constant current rate of 0.08-0.12C.
3. The chemical formation method according to claim 1, characterized in that: In step S1, the charge capacity of the lithium iron phosphate battery at this stage is 10-15% SOC.
4. The chemical formation method according to claim 1, characterized in that: In step S2, the total charge capacity of the lithium iron phosphate battery at this stage is 10-30% SOC.
5. The chemical formation method according to claim 1, characterized in that: In step S3, the battery is charged at a constant current rate of 0.1-0.15C.
6. The chemical formation method according to claim 1, characterized in that: In step S3, the total charge capacity of the lithium iron phosphate battery at this stage is 10-35% SOC.
7. A method for preparing a lithium iron phosphate battery, characterized in that: include: The positive and negative electrodes are wound into a battery cell, covered with an insulating film, placed in a square aluminum shell, and baked, injected, formed, and charged to make a lithium iron phosphate battery; The lithium iron phosphate battery is formed by the formation method of any one of claims 1 to 6.
8. The preparation method according to claim 7, characterized in that: The preparation method of the positive electrode sheet comprises: stirring, coating, cold pressing and slitting lithium iron phosphate, a conductive agent and a first binder in sequence to form a positive electrode sheet required for winding; wherein The conductive agent includes SP; The first binder includes PVDF.
9. The preparation method according to claim 7, characterized in that: The method for preparing the negative electrode sheet comprises: stirring, coating, cold pressing and slitting artificial graphite, a conductive agent and a second binder in sequence to form a negative electrode sheet required for winding; The second binder includes any one of CMC and SBR or a combination of the two.
10. A lithium iron phosphate battery, characterized in that: The lithium iron phosphate battery is manufactured by the preparation method of any one of claims 7 to 9.