Formation method of silicon negative electrode battery, battery and electric equipment

Abstract

The invention relates to the technical field of battery formation, in particular to a formation method of a silicon negative electrode battery, the battery and electric equipment. The formation method at least comprises the following steps: charging a battery cell infiltrated with an electrolyte to a first charge state; wherein the first state of charge is 100.5-102% of the rated capacity of the battery cell, and the negative electrode material of the battery comprises a silicon negative electrode material and a hard carbon material. According to the method, complete non-crystallization of the crystalline silicon in the formation process can be ensured, and secondary generation of a crystal phase Li15Si4 during deep lithium intercalation can be avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of battery formation, and in particular to a formation method of a silicon negative electrode battery, a battery and an electrical device. Background Art

[0002] The silicon anode has a high mass specific capacity (3579 mAh g -1 ) and low lithium insertion and removal potential (<0.5 V), is the preferred choice for the development of high-energy lithium-ion batteries. However, compared with graphite anode, high-capacity silicon anode has a high lithium insertion concentration (Li 15 Si4), the volume expansion is drastic (~300%), and most of the silicon negative electrode is crystalline. Due to the different lithium ion insertion and extraction barriers corresponding to different crystal faces of crystalline silicon, the lithium insertion dynamics in each crystal axis direction are different. The uneven lithiation process causes huge structural stress inside the material, inducing a large number of particle cracks in the later stage of lithium insertion and extraction, and finally the apparent volume expansion is more serious. Therefore, for the industrial application of silicon negative electrode, it is necessary to solve the problem of uneven lithium insertion and expansion of crystalline silicon.

[0003] In fact, crystalline silicon has begun to become amorphous during the first lithium insertion process. Some amorphous lithium-silicon alloys such as LiSi, Li 12 Si7 and Li 15 Si4 and other materials are generated successively. When the lithium insertion potential is lower than 60 mV (lithium insertion end), crystalline Li 15 The XRD diffraction peak of Si4 (J.Electrochem.Soc, 2007, 154, A156-A161) indicates that when the lithium insertion depth is too deep, Li 15 Si4, so for silicon negative electrode materials, in the formation stage, it is necessary not only to promote the complete amorphous phase transformation of crystalline silicon, but also to avoid the crystalline phase Li when deep lithium is inserted. 15 Secondary generation of Si4.

[0004] Therefore, a method is provided to ensure that the crystalline silicon is completely amorphized during the formation process and to avoid the formation of a crystalline phase Li when the lithium is deeply embedded. 15 The secondary formation method of Si4 is of great significance for improving the stability of silicon negative electrode during the cycle process. Summary of the Invention

[0005] The formation method and preparation method of the silicon-based negative electrode battery provided by the present invention can ensure that the crystalline silicon is completely amorphized during the formation process, and can avoid the formation of crystalline phase Li when deep lithium is inserted. 15 Secondary generation of Si4.

[0006] The battery provided by the present invention has high cycle stability.

[0007] The electrical equipment provided by the present invention has stable performance and long service life.

[0008] The present invention provides a formation method for a silicon negative electrode battery, which at least comprises:

[0009] Charging the battery cell soaked in the electrolyte to a first state of charge;

[0010] The first state of charge is 100.5-102% of the rated capacity of the battery cell, and the negative electrode material of the battery includes a silicon negative electrode material and a hard carbon material.

[0011] According to the above-mentioned formation method, the capacity of the hard carbon material is 0.1-5% of the capacity of the silicon negative electrode material.

[0012] According to the above-mentioned formation method, the capacity of the hard carbon material is 1-3% of the capacity of the silicon negative electrode material.

[0013] According to the above-described formation method, the first state of charge is 100.5-102% of the battery cell capacity.

[0014] The above-mentioned formation method further includes: charging the battery cell soaked in the electrolyte with a constant current I1 to a second state of charge, and then charging it with a constant current I2 to the first state of charge;

[0015] Among them, the second state of charge is 10-20% of the rated capacity of the battery cell.

[0016] According to the above-mentioned formation method, the current I1 is less than I2.

[0017] According to the above-mentioned formation method, the current I1 satisfies: 0.05C≤I1≤0.25.

[0018] According to the above-mentioned formation method, the current I2 satisfies: 0.5C≤I2≤1C.

[0019] The above-mentioned formation method further includes the step of discharging the battery cell after being charged to the first state of charge to a third state of charge, wherein the third state of charge is 0% of the rated capacity of the battery cell.

[0020] According to the above-mentioned formation method, the negative electrode material of the battery also includes graphite.

[0021] According to the above-mentioned formation method, the silicon negative electrode battery is a lithium ion battery.

[0022] The present invention also provides a method for preparing a battery, which includes a formation process using the above-mentioned formation method.

[0023] The present invention also provides a battery prepared by the above preparation method.

[0024] The present invention also provides an electrical device comprising the battery.

[0025] The formation method of the silicon negative electrode battery provided by the present invention, through the control of the charging process and the use of specific negative electrode materials, can not only promote the silicon negative electrode to complete the transformation of complete lithium insertion into amorphous state, promote the homogeneous lithium insertion expansion of the silicon negative electrode, reduce the risk of cycle degradation, but also avoid the formation of crystalline silicon during deep lithium insertion and reduce the risk of lithium plating. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The potential changes of silicon negative electrode and hard carbon negative electrode during charging process. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. 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 making creative efforts shall fall within the scope of protection of the present invention.

[0028] Based on the existing silicon negative electrode battery formation process, the negative electrode has a low degree of lithium insertion and is difficult to completely amorphize. In addition, when lithium is deeply inserted, a secondary crystalline phase Li 15 To solve the problem of Si4, the present invention provides a formation method of a silicon negative electrode battery, which at least includes: charging the battery cell after being soaked in electrolyte to a first state of charge, wherein the first state of charge is 100.5-102% of the rated capacity of the battery, and the negative electrode material of the battery includes a silicon negative electrode material and a hard carbon material.

[0029] The amorphization formation method for silicon negative electrode batteries provided by the present invention, when first charged to 100.5-102% of the rated capacity of the battery (i.e., overcharge), can promote the silicon negative electrode to complete the transformation to amorphization through complete lithium insertion, thereby ensuring homogeneous lithium insertion and expansion of the silicon negative electrode and reducing the risk of cyclic degradation. Moreover, because the negative electrode material contains a hard carbon material, the hard carbon material not only provides lithium insertion space, reducing the risk of lithium precipitation, but also competes with the silicon negative electrode for lithium insertion at the end of lithium insertion, ensuring that the lithium insertion potential of the silicon negative electrode is always above 60mV, thus avoiding the formation of crystalline silicon during deep lithium insertion. This is because the potential of the latter stage of lithium insertion (accounting for approximately 40% of the lithium insertion capacity of the hard carbon) is close to 0V, and the hard carbon material has higher kinetic properties, which can compete with the silicon negative electrode for low-potential lithium insertion. During the actual charge and discharge process, the actual potential of the silicon negative electrode is always above 60mV, that is, the silicon negative electrode is always in an amorphous lithium insertion and deintercalation state.

[0030] The principle of competition between hard carbon and silicon negative electrodes for lithium insertion can be found in Figure 1 ,Depend on Figure 1As can be seen, as charging progresses, the negative electrode voltage gradually decreases. When the voltage is below 300mV, the lithium insertion potential of the hard carbon material begins to be lower than that of the silicon negative electrode. In other words, thermodynamically, both the hard carbon negative electrode and the silicon negative electrode will participate in the low-potential lithium insertion reaction (at the end of charging). However, because the lithium insertion kinetics of the hard carbon negative electrode are much higher than those of the silicon negative electrode, at the end of the lithium insertion of the battery cell, the main lithium insertion reaction occurs mainly in the hard carbon negative electrode, and the silicon negative electrode is in an incompletely inserted state (amorphous state). Without a hard carbon negative electrode, the silicon negative electrode is in a fully inserted crystalline state at the end of the lithium insertion, which will lead to problems with stress orientation and uneven distribution, thereby degrading the cycling and expansion performance.

[0031] In the present invention, the silicon anode material is not specifically limited and can be, for example, pure silicon (nano- or micro-silicon), silicon oxide, or silicon-carbon material. The hard carbon material is also not specifically limited and can be, for example, hard carbon materials prepared from biomass materials, polymers, and fossil fuels.

[0032] The battery cell is not specifically limited and can be, for example, a lithium-ion battery cell, a sodium-ion battery cell, or a potassium-ion battery cell, and can be prepared according to conventional methods in the art. The electrolyte is not specifically limited and can be a conventional electrolyte in the art.

[0033] It can also be understood that battery formation is a key process in battery production. Its core goal is to form a stable solid electrolyte film (SEI film) on the surface of the negative electrode through the first charge and discharge process and activate the active substances inside the battery. Therefore, the initial state of charge during battery formation is generally 0.

[0034] In the present invention, considering the system's energy density and the need to better avoid lithium plating, the capacity of the hard carbon material is typically controlled to be 0.1-5% of the silicon anode capacity. For example, the capacity of the hard carbon material can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any range between any two of these values. When the capacity of the hard carbon material is 1-3% of the silicon anode capacity, the overall performance of the system is even better.

[0035] It should be noted that the capacity mentioned above refers to the lithium insertion capacity, which is determined by the properties of the material itself and the content of the material.

[0036] Charging to a first state of charge of 100.5-102% of the rated capacity of the battery can promote the silicon negative electrode to complete the transformation of complete lithium insertion and amorphization, thereby promoting the homogeneous lithium insertion and expansion of the silicon negative electrode and reducing the risk of cycle degradation. When the charge is too high, the negative electrode is at risk of lithium plating. Therefore, in the present invention, it is preferred to charge to a first state of charge of 100.5-101% of the rated capacity of the battery, which is more conducive to controlling the complete amorphization of the silicon negative electrode and controlling the lithium plating problem.

[0037] In some embodiments, the formation method for the silicon negative electrode battery further includes charging the electrolyte-soaked cell with a constant current I1 to a second state of charge, and then charging it with a constant current I2 to a first state of charge; wherein the second state of charge is 10-20% of the rated capacity of the cell. This formation charging method is beneficial for further improving film quality and shortening production cycles.

[0038] Furthermore, when current I1 < I2, it is beneficial to further improve the film quality. Specifically: since the chemical film formation is mainly concentrated in the first 10% SOC charging stage, performing low current film formation during the film formation stage can effectively improve the film formation stability, while subsequent high current charging can effectively reduce the chemical formation time, thereby improving production efficiency.

[0039] In actual operation, in order to take into account both film formation time and film formation quality, the current I1 is usually controlled to meet 0.05C≤I1≤0.25C, and the current I2 is controlled to meet: 0.5C≤I2≤1C.

[0040] It is understandable that the formation method generally also includes the step of discharging the battery cell after charging to the first state of charge. In some specific embodiments of the present invention, the formation method of the above-mentioned silicon negative electrode battery also includes discharging the battery cell after charging to the first state of charge to a third state of charge, wherein the third state of charge is 0% of the rated capacity of the battery cell. Discharging it to 0% of the rated capacity of the battery cell can ensure that the gel starting stage is 0% SOC. When the gel starting stage is 0% SOC, it is conducive to the high temperature and high pressure reconstruction of the binder network. This is because the negative electrode particles are in the process of gradual lithium insertion and expansion. The binder network will be accompanied by the expansion of the negative electrode particles, thereby performing secondary distribution, which is beneficial to the suppression of battery cell expansion and the improvement of cycle performance. The gel process is generally controlled at a temperature of 60-85°C and a pressure of 1.0-1.2Mpa for 60-120min.

[0041] In some embodiments, the negative electrode material of the battery further includes graphite, soft carbon, activated carbon, etc.

[0042] The silicon negative electrode battery provided by the present invention is not particularly limited, and may be, for example, a lithium ion battery, a sodium ion battery, a potassium ion battery, etc. In some embodiments, the silicon negative electrode battery is a lithium ion battery.

[0043] The present invention also provides a method for preparing a battery, comprising a formation process using the above-mentioned formation method. The battery prepared using this method has good cycle stability.

[0044] The present invention also provides a battery produced by the above-described method. The battery type is not specifically limited, and may be a lithium-ion battery, a sodium-ion battery, a potassium-ion battery, or the like. It may be a liquid battery, a solid-state battery, or a quasi-solid-state battery. It may be a soft-pack battery or a hard-shell battery.

[0045] The present invention also provides an electrical device comprising the aforementioned battery. The device can be conventional electrical devices in the art, including consumer electronics (mobile communication devices, laptops, tablet computers, wearable devices, etc.), drones, power tools, energy storage devices, electric bicycles, electric vehicles, and the like.

[0046] The battery formation process of the present invention is described in detail below with reference to specific embodiments.

[0047] Example 1

[0048] This embodiment provides a formation process and preparation method for a lithium-ion battery having a rated capacity of 5 Ah, and the steps are as follows:

[0049] (1) Provide batteries to be formed

[0050] The positive and negative electrode materials are homogenized, coated, baked, rolled, and then cut into positive and negative electrode sheets of the required specifications. The positive electrode slurry is: active material lithium iron phosphate, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black. The mass ratio of the three is 94:3:3. The solvent is N-methylpyrrolidone, and the positive electrode current collector is aluminum foil.

[0051] The negative electrode slurry is: active material graphite, nano-silicon negative electrode and coconut shell-based hard carbon, the binder is PAA-Li and SBR, and the conductive agent is acetylene black. The mass ratio of graphite, nano-silicon negative electrode and coconut shell-based hard carbon is 90:7:3, the mass ratio of PAA-Li and SBR is 2:1, the mass ratio of active material, binder and conductive agent is 94:3:3, the solvent is deionized water, and the negative electrode sheet is copper foil. The hard carbon capacity is 0.95% of the silicon negative electrode capacity.

[0052] The prepared positive and negative electrode sheets are stacked or wound with a separator, separated by a separator, and the electrode tabs are welded to form a battery cell. The separator is made of polypropylene (PP).

[0053] The battery cell is encased in a casing, covered with a cover, and baked at 90°C for 16 hours. The electrolyte is then added and allowed to soak at 25°C for 35 hours before being placed in a formation cabinet for formation. The electrolyte used for injection consists of the lithium salt LiPF6 and the solvent ethylene carbonate (EC), with a lithium salt concentration of 1.2 mol / L.

[0054] (2) Chemical formation process

[0055] The prepared battery was charged at a constant current of 0.1 C until the state of charge (SOC) of the battery reached 15% SOC, and then left for 10 minutes;

[0056] The battery that has completed the first charging operation is charged to 100.8% SOC using a constant current of 0.6C and then left for 10 minutes.

[0057] The charged battery was discharged at a constant current of 0.6C to 0% SOC, then left for 10 minutes, and then left for 100 minutes at 80°C and a pressure of 1.1 MPa to complete the gelling process.

[0058] After the gel is completed, the air is evacuated and sealed, and then the airbag is sealed, the airbag is cut, and the edge is folded to obtain the finished soft-pack battery.

[0059] Example 2

[0060] The difference between this embodiment and embodiment 1 is that the first state of charge is 100.5%.

[0061] Example 3

[0062] The difference between this embodiment and embodiment 1 is that the first state of charge is 101%.

[0063] Example 4

[0064] The difference between this embodiment and embodiment 1 is that the first state of charge is 102%.

[0065] Example 5

[0066] The difference between this embodiment and embodiment 1 is that the capacity of the hard carbon material in the negative electrode material is 0.1% of the capacity of the silicon negative electrode.

[0067] Example 6

[0068] The difference between this embodiment and embodiment 1 is that the capacity of the hard carbon material in the negative electrode material is 0.5% of the capacity of the silicon negative electrode.

[0069] Example 7

[0070] The difference between this embodiment and embodiment 1 is that the capacity of the hard carbon material in the negative electrode material is 1% of the capacity of the silicon negative electrode.

[0071] Example 8

[0072] The difference between this embodiment and embodiment 1 is that the capacity of the hard carbon material in the negative electrode material is 3% of the capacity of the silicon negative electrode.

[0073] Example 9

[0074] The difference between this embodiment and embodiment 1 is that the capacity of the hard carbon material in the negative electrode material is 5% of the capacity of the silicon negative electrode.

[0075] Example 10

[0076] The difference between this embodiment and embodiment 1 is that the currents in the formation steps I1 and I2 are 0.2C and 0.5C respectively.

[0077] Example 11

[0078] The difference between this embodiment and embodiment 1 is that the currents in the formation steps I1 and I2 are 0.05C and 1C respectively.

[0079] Example 12

[0080] The difference between this embodiment and embodiment 1 is that there is no I1 current in the formation process, and the I2 current is 0.6C.

[0081] Example 13

[0082] The difference between this embodiment and embodiment 1 is that the silicon negative electrode in the negative electrode material is a micron silicon oxide material.

[0083] Example 14

[0084] The difference between this embodiment and embodiment 1 is that the silicon negative electrode in the negative electrode material is a micron silicon-carbon material.

[0085] Example 15

[0086] The difference between this embodiment and embodiment 1 is that the hard carbon in the negative electrode material is phenolic resin-based hard carbon.

[0087] Example 16

[0088] The difference between this embodiment and embodiment 1 is that the hard carbon in the negative electrode material is PVA-based organic polymer hard carbon.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 1 is that the first state of charge during formation is 105%.

[0091] Comparative Example 2

[0092] The difference between this comparative example and Example 1 is that the first state of charge is 100%.

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 1 is that the negative electrode material of the battery does not contain hard carbon material. Specifically, the negative electrode slurry is active material graphite and nano-silicon negative electrode; the binder is PAA-Li and SBR; the conductive agent is acetylene black, and the mass ratio of the three is (93:7): (2:1):3; the solvent is deionized water, and the negative electrode sheet is copper foil. The other production processes are the same as in Example 1.

[0095] Performance testing:

[0096] The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to a high-temperature cycle test. The high-temperature charge-discharge cycle test conditions were 1C charging and 1C discharging (1C = 5A) at 45°C. The thickness expansion rate and capacity retention rate of the battery after 500 cycles at 45°C were calculated. The test results are shown in Table 1.

[0097] Table 1 Battery performance test results

[0098]

[0099] It can be seen from the results in Table 1 that, compared with the comparative example, the silicon negative electrode cell obtained in the embodiment of the present application has the advantages of low thickness expansion rate and high capacity retention rate.

[0100] In addition, appropriate hard carbon addition, overcharge SOC, and formation current are beneficial to inhibiting the degree of crystallization of silicon negative electrode materials and improving film quality, thereby improving cycle stability and reducing thickness expansion rate.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A formation method for a silicon negative electrode battery, characterized in that: At least: Charging the battery cell soaked in the electrolyte to a first state of charge; The first state of charge is 100.5-102% of the rated capacity of the battery cell, and the negative electrode material of the battery includes a silicon negative electrode material and a hard carbon material.

2. The formation method of the silicon negative electrode battery according to claim 1, characterized in that: The capacity of the hard carbon material is 0.1-5% of the capacity of the silicon negative electrode material.

3. The formation method of the silicon negative electrode battery according to claim 1 or 2, characterized in that: The first state of charge is 100.5-101% of the battery cell capacity.

4. The formation method of a silicon negative electrode battery according to any one of claims 1 to 3, characterized in that: Also includes: After the battery cell is soaked in the electrolyte, it is charged to the second state of charge with a constant current of I1, and then charged to the first state of charge with a constant current of I2; Among them, the second state of charge is 10-20% of the rated capacity of the battery cell.

5. The formation method of a silicon negative electrode battery according to any one of claims 1 to 4, characterized in that: The current I1<I2.

6. The formation method of a silicon negative electrode battery according to any one of claims 1 to 5, characterized in that: The current I1 satisfies: 0.05C≤I1≤0.25C; and / or The current I2 satisfies: 0.5C≤I2≤1C.

7. The formation method of a silicon negative electrode battery according to any one of claims 1 to 6, characterized in that: The method further includes discharging the battery cell after being charged to the first state of charge to a third state of charge, wherein the third state of charge is 0% of the rated capacity of the battery cell.

8. The formation method of a silicon negative electrode battery according to any one of claims 1 to 7, characterized in that: The negative electrode material of the battery further includes graphite.

9. The formation method of a silicon negative electrode battery according to any one of claims 1 to 8, characterized in that: The silicon negative electrode battery is a lithium ion battery.

10. A method for preparing a battery, characterized in that: The invention comprises a process of chemical formation using the chemical formation method according to any one of claims 1 to 9.

11. A battery, characterized in that: The method according to claim 10 is used to prepare the compound.

12. An electrical device, characterized in that: Including the battery according to claim 11.

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