Lithium ion battery formation method and lithium ion battery

Abstract

Embodiments of the present invention provide a lithium-ion battery formation method and a lithium-ion battery, relating to the field of battery technology. The lithium-ion battery formation method is applied to a lithium-ion battery containing a lithium-supplementing additive. The formation method comprises: performing constant current charging of the lithium-ion battery at a preset temperature with a first current until the voltage is greater than or equal to the first preset voltage; performing pulse charging of the lithium-ion battery with a second current; and performing pulse discharging of the lithium-ion battery with a third current until the voltage of the lithium-ion battery reaches the second preset voltage. This method can reduce side reactions between the electrolyte and the lithium-supplementing additive at high voltage, thereby improving the cycle performance of the lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium ion battery formation method and a lithium ion battery. Background Art

[0002] Formation is a very complex process in the production of lithium-ion batteries and is also an important process that affects battery performance. During formation, a dense passivation film (solid electrolyte interface film, referred to as SEI film) is formed on the surface of the battery's negative electrode. The quality, stability and interface optimization of the SEI film are important factors that cannot be ignored in determining the battery life. Different formation processes form different SEI films, resulting in great differences in lithium-ion battery performance.

[0003] In order to improve the electrochemical performance of lithium-ion batteries, lithium-supplementing additives are added to the positive electrode of the battery. Lithium-supplementing additives can only exert higher capacity under high voltage. However, the existing formation method does not consume much lithium-supplementing additives, which will cause the electrolyte to have a large side reaction with the lithium-supplementing additives under high voltage, thereby causing the cycle performance of the lithium-ion battery to deteriorate. Summary of the Invention

[0004] The present invention aims to provide a lithium-ion battery formation method that can reduce the side reactions between the electrolyte and the lithium-supplementing additive at high voltages, thereby improving the cycle performance of the lithium-ion battery.

[0005] Another object of the present invention is to provide a lithium-ion battery that can reduce the side reactions between the electrolyte and the lithium-supplementing additive at high voltages, thereby improving the cycle performance of the lithium-ion battery.

[0006] The embodiments of the present invention can be implemented as follows:

[0007] An embodiment of the present invention provides a lithium-ion battery formation method, which is applied to a lithium-ion battery containing a lithium-supplementing additive. The formation method comprises:

[0008] At a preset temperature, constant-current charging the lithium-ion battery with a first current until the voltage of the lithium-ion battery is greater than or equal to a first preset voltage;

[0009] pulse charging the lithium-ion battery with a second current;

[0010] The lithium-ion battery is pulse-discharged with a third current so that the voltage of the lithium-ion battery reaches a second preset voltage, wherein the first preset voltage is lower than the second preset voltage.

[0011] Optionally, the first current is 0.01C to 0.5C, the second current is greater than or equal to 0.3C, and the third current is 1C to 3C;

[0012] The first preset voltage is 3.5V to 3.8V, and the second preset voltage is 4.0V to 4.5V;

[0013] The time for pulse charging with the second current is 15s to 120s, and the time for pulse discharging with the third current is 0 to 20s;

[0014] The preset temperature is 25-60°C.

[0015] Optionally, the preset temperature is 45°C, the first current is 0.01C, the second current is 1C, the third current is 2C, the first preset voltage is 3.5V, the second preset voltage is 4.3V, the time for pulse charging with the second current is 30s, and the time for pulse discharging with the third current is 5s.

[0016] Optionally, the preset temperature is 45°C, the first current is 0.01C, the second current is 0.8C, the third current is 2C, the first preset voltage is 3.5V, the second preset voltage is 4.3V, the time for pulse charging with the second current is 30s, and the time for pulse discharging with the third current is 5s.

[0017] Optionally, the preset temperature is 45°C, the first current is 0.01C, the second current is 0.6C, the third current is 2C, the first preset voltage is 3.6V, the second preset voltage is 4.3V, the time for pulse charging with the second current is 60s, and the time for pulse discharging with the third current is 5s.

[0018] Optionally, the preset temperature is 45°C, the first current is 0.01C, the second current is 0.8C, the third current is 2C, the first preset voltage is 3.6V, the second preset voltage is 4.2V, the time for pulse charging with the second current is 30s, and the time for pulse discharging with the third current is 5s.

[0019] Optionally, the preset temperature is 60°C, the first current is 0.01C, the second current is 0.8C, the third current is 2C, the first preset voltage is 3.6V, the second preset voltage is 4.2V, the time for pulse charging with the second current is 30s, and the time for pulse discharging with the third current is 5s.

[0020] Optionally, the preset temperature is 45°C, the first current is 0.01C, the second current is 1C, the third current is 2C, the first preset voltage is 3.6V, the second preset voltage is 4.4V, the time for pulse charging with the second current is 30s, and the time for pulse discharging with the third current is 5s.

[0021] Optionally, the step of pulse charging the lithium-ion battery with the second current to the step of pulse discharging the lithium-ion battery with the third current are cycled until the second preset voltage is reached.

[0022] An embodiment of the present invention further provides a lithium-ion battery manufactured by the above-mentioned lithium-ion battery formation method.

[0023] The lithium-ion battery formation method and the lithium-ion battery of the embodiments of the present invention have beneficial effects, for example: first, at a preset temperature, the lithium-ion battery is constant-current charged with a first current until the voltage is greater than or equal to the first preset voltage, at which time the consumption voltage of the lithium-supplementing additive is reached; then, the lithium-ion battery is pulse-charged with a second current, and then the lithium-ion battery is pulse-discharged with a third current. The use of pulse charging and pulse discharging can increase the consumption of the lithium-supplementing additive, thereby reducing the side reaction of the electrolyte with the lithium-supplementing additive at high voltage and improving the cycle performance of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is a flow chart of the lithium-ion battery formation method of this application. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0028] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0029] In the description of the present invention, it should be noted that if the terms "upper", "lower", "inside", "outside", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the invention is usually placed when in use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be understood as a limitation on the present invention.

[0030] In addition, the terms "first", "second", etc., if used, are merely used to distinguish and describe, and should not be understood as indicating or implying relative importance.

[0031] It should be noted that, in the absence of conflict, the features in the embodiments of the present invention may be combined with each other.

[0032] The inventors of this application have discovered that existing formation methods lead to increased side reactions between the electrolyte and lithium-supplementing additives at high voltages, which in turn leads to poor cycle performance of lithium-ion batteries. This embodiment provides a lithium-ion battery formation method that at least addresses this technical problem.

[0033] Please refer to Figure 1 The lithium-ion battery formation method provided in this embodiment is applied to a lithium-ion battery containing a lithium supplement additive, and the formation method comprises:

[0034] Step S100: performing constant current charging on the lithium-ion battery at a preset temperature with a first current until the voltage of the lithium-ion battery is greater than or equal to a first preset voltage.

[0035] It should be noted that the first preset voltage is the minimum voltage at which the lithium-replenishing additive can be consumed. Using the formation charge-discharge device to perform constant current charging of the lithium-ion battery at a first current to a voltage greater than or equal to the first preset voltage provides the necessary conditions for consuming the lithium-replenishing additive. This embodiment uses Li₅FeO₄ as an example of a lithium-replenishing additive.

[0036] Step S200: pulse charging the lithium-ion battery with a second current.

[0037] It should be noted that the use of formation charge and discharge equipment with a second current adopts a pulse charging oscillation mode for the lithium-ion battery to promote the conversion of the lithium supplement additive Li5FeO4, increase the release of oxygen elements, and consume the lithium supplement additive Li5FeO4 in advance. This can reduce the side reaction of the electrolyte with the lithium supplement additive Li5FeO4 at high voltage, thereby improving the cycle performance of the lithium-ion battery.

[0038] Step S300: pulse-discharge the lithium-ion battery with a third current.

[0039] It should be noted that the use of formation charge and discharge equipment with a third current to adopt a pulse discharge oscillation mode for lithium-ion batteries promotes the conversion of the lithium supplement additive Li5FeO4, increases the release of oxygen elements, and consumes the lithium supplement additive Li5FeO4 in advance. This can reduce the side reaction of the electrolyte with the lithium supplement additive Li5FeO4 at high voltage, thereby improving the cycle performance of the lithium-ion battery.

[0040] Step S400 , looping step S200 to step S300 until the voltage of the lithium-ion battery reaches a second preset voltage, wherein the first preset voltage is lower than the second preset voltage.

[0041] It should be noted that the second preset voltage is a cut-off voltage.

[0042] In an optional embodiment, the first current is 0.01C~0.5C, the second current is greater than or equal to 0.3C, and the third current is 1C~3C; the first preset voltage is 3.5V~3.8V, and the second preset voltage is 4.0~4.5V; the time for pulse charging with the second current is 15s~120s, and the time for pulse discharging with the third current is 0~20s; the preset temperature is 25~60℃.

[0043] For example, the first current can be 0.01C, 0.05C, 0.1C, 0.2C, 0.3C, or 0.5C; the second current can be 0.3C, 0.5C, 0.8C, 1C, 1.2C, or 1.5C; and the third current can be 1C, 1.5C, 2C, 2.5C, or 3C. The duration of pulse charging with the second current can be 15s, 30s, 60s, 90s, or 120s; the duration of pulse discharging with the third current can be 1s, 2s, 3s, 5s, 10s, 15s, or 20s. The preset temperature can be 25°C, 35°C, 45°C, 55°C, or 60°C.

[0044] Example 1:

[0045] The preset temperature is 45°C, the first current is 0.01C, the second current is 1C, the third current is 2C, the first preset voltage is 3.5V, the second preset voltage is 4.3V, the pulse charging time with the second current is 30 seconds, and the pulse discharging time with the third current is 5 seconds. This embodiment uses a 5Ah lithium-ion battery as an example.

[0046] The formation method includes: at a preset temperature of 45°C, constant current charging the lithium-ion battery at a current of 0.01C (0.05A) until the voltage is equal to 3.5V, then pulse charging the lithium-ion battery at a current of 1C (5A) for 30s, and then pulse discharging the lithium-ion battery at a current of 2C (10A) for 5s, and cycling until the voltage is equal to 4.3V to obtain a formed lithium-ion battery.

[0047] It should be noted that lithium-ion batteries are placed in a soft-pack formation cabinet for formation. The use of pulse charging and pulse discharging methods can shorten the formation time and improve production efficiency.

[0048] This embodiment also provides a lithium-ion battery, which is manufactured by the above-mentioned lithium-ion battery formation method.

[0049] The lithium-ion battery is prepared by the following preparation method before being formed by the above-mentioned lithium-ion battery formation method: 1) Li5FeO4, lithium iron phosphate, Super P, carbon nanotubes, and polyvinylidene fluoride are prepared into a positive electrode slurry with a mass ratio of 2%, 95%, 0.5%, 0.5%, and 2% respectively, and the prepared slurry is then evenly coated on aluminum foil using a transfer coater. After being dried in an oven at a certain temperature, the dried electrode sheet is rolled and die-cut to form a positive electrode sheet. 2) Graphite, conductive carbon black Super P, hydroxyethyl cellulose CMC, and styrene-butadiene rubber SBR are prepared into a negative electrode slurry with a mass ratio of 96:1:1.5:1.5 respectively, and after being dried in an oven at a certain temperature, the negative electrode sheet is die-cut. 3) The prepared positive electrode sheet, negative electrode sheet, electrolyte and separator are assembled into a 5Ah lithium-ion battery, where the electrolyte and separator are conventionally used in existing lithium-ion batteries.

[0050] It should be noted that the positive electrode sheet includes Li5FeO4, a positive electrode active material, a composite conductive agent, and a binder. The mass ratio of Li5FeO4 to the positive electrode active material is ((0.05-12):(88-99.5)), where the Li5FeO4 can be selected in the range of 0.05, 0.2, 0.25, 0.3, 1, 2, 5, and 12; the positive electrode active material can be selected in the range of 88, 95, 98, 97, 97.5, 98, and 99.5. The positive electrode active material includes at least one of lithium iron phosphate and a ternary material. The composite conductive agent includes conductive carbon black and / or carbon nanotubes. The binder includes polyvinylidene fluoride. The combined mass of the composite conductive agent and the binder accounts for 1-5% of the total mass of the positive electrode sheet, for example, 1%, 1.5%, 2%, 3%, 4%, 5%, etc. The negative electrode sheet contains graphite and / or silicon. The positive electrode sheet in lithium-ion batteries contains a lithium-supplementing additive, Li5FeO4, with a gram capacity of >700mAh / g. This additive compensates for the initial consumption of active lithium in the negative electrode, improving the battery system's energy density and long-cycle performance. After pulsed current formation, the positive electrode sheet of the lithium-ion battery contains little or no Li5FeO4, reducing subsequent gassing and improving the battery's high-temperature storage stability.

[0051] Example 2:

[0052] The difference between this embodiment and the first embodiment is that the second current is 0.8C.

[0053] The formation method includes: at a preset temperature of 45°C, charging the lithium-ion battery with a constant current of 0.01C (0.05A) until the voltage is equal to 3.5V, then pulse charging the lithium-ion battery with a current of 0.8C (4A) for 30s, and then pulse discharging the lithium-ion battery with a current of 2C (10A) for 5s, and cycling until the voltage is equal to 4.3V.

[0054] Example 3:

[0055] The difference between this embodiment and the first embodiment is that the second current is 0.6C, the first preset voltage is 3.6V, and the time for pulse charging with the second current is 60s.

[0056] The formation method includes: at a preset temperature of 45°C, constant current charging the lithium-ion battery at a current of 0.01C (0.05A) until the voltage is equal to 3.6V, then pulse charging the lithium-ion battery at a current of 0.6C (3A) for 60s, and then pulse discharging the lithium-ion battery at a current of 2C (10A) for 5s, and cycling until the voltage is equal to 4.3V.

[0057] Example 4:

[0058] The difference between this embodiment and the first embodiment is that the second current is 0.8C, the first preset voltage is 3.6V, and the second preset voltage is 4.2V.

[0059] The formation method includes: at a preset temperature of 45°C, constant current charging the lithium-ion battery at a current of 0.01C (0.05A) until the voltage is equal to 3.6V, then pulse charging the lithium-ion battery at a current of 0.8C for 30s, and then pulse discharging the lithium-ion battery at a current of 2C for 5s, and cycling until the voltage is equal to 4.2V.

[0060] Embodiment 5:

[0061] The difference between this embodiment and the first embodiment is that the preset temperature is 60° C., the second current is 0.8° C., the first preset voltage is 3.6V, and the second preset voltage is 4.2V.

[0062] The formation method includes: at a preset temperature of 60°C, charging the lithium-ion battery with a constant current of 0.01C until the voltage is equal to 3.6V, then pulse charging the lithium-ion battery with a current of 0.8C for 30s, and then pulse discharging with a current of 2C for 5s, and cycling until the voltage is equal to 4.2V.

[0063] Example 6:

[0064] The difference between this embodiment and the first embodiment is that the first preset voltage is 3.6V and the second preset voltage is 4.4V.

[0065] The formation method includes: at a preset temperature of 45°C, charging the lithium-ion battery with a constant current of 0.01C until the voltage is equal to 3.6V, then pulse charging the lithium-ion battery with a current of 1C for 30s, and then pulse discharging the lithium-ion battery with a current of 2C for 5s, and cycling until the voltage is equal to 4.4V.

[0066] Comparative Example:

[0067] The difference between the comparative example and the first embodiment is that the battery is charged at a constant current of 0.01C (0.05A) to a cut-off voltage of 4.3V to obtain a formed lithium-ion battery.

[0068] Performance testing was conducted on 5Ah lithium-ion batteries produced using the formation methods described in Examples 1-6 and the comparative example, prepared according to GB / T 31467.3-2015. The test standard was to discharge the battery to 2.5V at a constant current of 0.33°C at room temperature. The initial discharge capacity was recorded, the initial coulombic efficiency was calculated, and the discharge capacity retention after 100 cycles at 1C / 1C at 25°C was measured. The results are shown in the table below.

[0069] First discharge capacity First coulombic efficiency Capacity retention rate Example 1 5.05 86.6％ 98％ Example 2 5.15 87.5％ 99％ Example 3 4.98 86.1％ 97％ Example 4 5.02 86.5％ 98％ Example 5 4.92 85.5％ 97％ Example 6 5.08 86.8％ 96％ Comparative Example 4.87 85.2％ 95％

[0070] The following conclusions can be drawn from the data in the table:

[0071] The formation method provided by the present invention adopts processes such as high temperature, pressurization and pulse current oscillation, and accelerates the consumption of the lithium supplement additive Li5FeO4 by performing pulse charging and pulse discharging, thereby improving the density of the SEI film and enhancing the battery performance; compared with the comparative example, Examples 1-6 prepare lithium-ion batteries with higher first discharge capacity, first coulomb efficiency and capacity retention rate, and the higher first discharge capacity, first coulomb efficiency and capacity retention rate indicate that the consumption of the lithium supplement additive Li5FeO4 is relatively large.

[0072] In summary, the embodiments of the present invention provide a lithium-ion battery formation method and a lithium-ion battery, which use pulse charging and pulse discharging to accelerate the consumption of the lithium-supplementing additive Li5FeO4, thereby reducing the side reaction of the electrolyte with the lithium-supplementing additive Li5FeO4 at high voltage and improving the cycle performance of the lithium-ion battery.

[0073] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A lithium ion battery formation method, characterized in that: Applied to lithium-ion batteries containing lithium-supplementing additives, the formation method includes: At a preset temperature, constant current charging the lithium-ion battery with a first current until the voltage of the lithium-ion battery is greater than or equal to a first preset voltage; pulse charging the lithium-ion battery with a second current; Pulse-discharging the lithium-ion battery with a third current so that the voltage of the lithium-ion battery reaches a second preset voltage, wherein the first preset voltage is less than the second preset voltage; The first preset voltage is the lowest voltage that the lithium supplement additive can consume; Cycling the steps of pulse charging the lithium-ion battery with the second current to pulse discharging the lithium-ion battery with the third current until a second preset voltage is reached, wherein the second preset voltage is a cut-off voltage; The first current is 0.01C to 0.5C, the second current is greater than or equal to 0.3C, and the third current is 1C to 3C; The first preset voltage is 3.5V to 3.8V, and the second preset voltage is 4.0V to 4.5V; The time for pulse charging with the second current is 15s to 120s, and the time for pulse discharging with the third current is 0 to 20s; The preset temperature is 25-60°C.

2. The lithium ion battery formation method according to claim 1, wherein The preset temperature is 45°C, the first current is 0.01C, the second current is 1C, the third current is 2C, the first preset voltage is 3.5V, the second preset voltage is 4.3V, the time for pulse charging with the second current is 30s, and the time for pulse discharging with the third current is 5s.

3. The lithium ion battery formation method according to claim 1, wherein The preset temperature is 45°C, the first current is 0.01C, the second current is 0.8C, the third current is 2C, the first preset voltage is 3.5V, the second preset voltage is 4.3V, the time for pulse charging with the second current is 30s, and the time for pulse discharging with the third current is 5s.

4. The lithium ion battery formation method according to claim 1, wherein The preset temperature is 45°C, the first current is 0.01C, the second current is 0.6C, the third current is 2C, the first preset voltage is 3.6V, the second preset voltage is 4.3V, the time for pulse charging with the second current is 60s, and the time for pulse discharging with the third current is 5s.

5. The lithium ion battery formation method according to claim 1, wherein The preset temperature is 45°C, the first current is 0.01C, the second current is 0.8C, the third current is 2C, the first preset voltage is 3.6V, the second preset voltage is 4.2V, the time for pulse charging with the second current is 30s, and the time for pulse discharging with the third current is 5s.

6. The lithium ion battery formation method according to claim 1, characterized in that: The preset temperature is 60°C, the first current is 0.01C, the second current is 0.8C, the third current is 2C, the first preset voltage is 3.6V, the second preset voltage is 4.2V, the time for pulse charging with the second current is 30s, and the time for pulse discharging with the third current is 5s.

7. The lithium ion battery formation method according to claim 1, characterized in that: The preset temperature is 45°C, the first current is 0.01C, the second current is 1C, the third current is 2C, the first preset voltage is 3.6V, the second preset voltage is 4.4V, the time for pulse charging with the second current is 30s, and the time for pulse discharging with the third current is 5s.

8. A lithium ion battery, characterized in that: The lithium ion battery is manufactured by the lithium ion battery formation method according to any one of claims 1 to 7.

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