Electrochemical device charging and discharging methods, electrochemical devices and electronic equipment

Abstract

This invention relates to a charging and discharging method for an electrochemical device, an electrochemical device, and an electronic device. The method includes: if the thickness change rate is less than a first thickness change rate threshold, then performing charge-discharge cycles on the electrochemical device based on the charging cut-off voltage and the discharging cut-off voltage of the electrochemical device; if the thickness change rate reaches the first thickness change rate threshold, then increasing the discharging cut-off voltage, and performing charge-discharge cycles on the electrochemical device based on the charging cut-off voltage and the increased discharging cut-off voltage; if the thickness change rate reaches a second thickness change rate threshold, then further increasing the discharging cut-off voltage, and performing charge-discharge cycles on the electrochemical device based on the charging cut-off voltage and the further increased discharging cut-off voltage. This invention solves the technical problem of decreased cycle performance or even failure of electrochemical devices due to volume expansion during charge-discharge cycles, achieving the technical effect of suppressing the volume expansion effect of electrochemical devices and improving their cycle performance.

Description

Technical Field

[0001] This invention relates to the field of battery energy storage technology, and in particular to a charging and discharging method for an electrochemical device, an electrochemical device, and an electronic device. Background Technology

[0002] The anode is a crucial component of lithium-ion batteries, directly impacting their cycle performance. Carbon-based materials were the first commercially available anode materials for lithium-ion batteries, boasting advantages such as high conductivity, strong stability, and readily available raw materials. However, their relatively low theoretical specific capacity (372 mAh / g) is insufficient to meet the ever-increasing energy storage demands. Therefore, high-capacity silicon-based materials have gradually become a research hotspot. Silicon's theoretical specific capacity at room temperature can reach 3600 mAh / g; however, its significant volume expansion is a key issue limiting its application in lithium-ion anode materials. Currently, methods to improve silicon-based anode materials include reducing silicon particle size, carbon coating, increasing silicon particle porosity, and interface modification, primarily focusing on improving the performance of the silicon-based anode material itself. During cycling, silicon-doped anode batteries experience lithium-ion alloying reactions with silicon, resulting in both lithium insertion and extraction accompanied by lithium degradation. x Changes in the Si phase and repeated expansion of silicon gradually destroy the stable structure of silicon, resulting in a significant decrease in cycle performance.

[0003] There is currently no effective solution to the problem that electrochemical devices in related technologies suffer from reduced cycle performance or even failure due to volume expansion during charge-discharge cycles. Summary of the Invention

[0004] The present invention provides a charging and discharging method for an electrochemical device, an electrochemical device, and an electronic device, which at least solves the technical problem that the electrochemical device's cycle performance deteriorates or even fails due to volume expansion during the charging and discharging cycle.

[0005] According to one aspect of the present invention, a method for charging and discharging an electrochemical device is provided, comprising: obtaining the thickness change rate of the electrochemical device after multiple charge-discharge cycles; when the thickness change rate is less than a first thickness change rate threshold, performing charge-discharge cycles on the electrochemical device according to a charging cut-off voltage and a discharging cut-off voltage; when the thickness change rate is greater than or equal to the first thickness change rate threshold and less than a second thickness change rate threshold, increasing the discharging cut-off voltage and performing charge-discharge cycles on the electrochemical device according to the charging cut-off voltage and the increased discharging cut-off voltage; when the thickness change rate is greater than or equal to the second thickness change rate threshold, further increasing the discharging cut-off voltage and performing charge-discharge cycles on the electrochemical device according to the charging cut-off voltage and the further increased discharging cut-off voltage; wherein the first thickness change rate threshold is less than the second thickness change rate threshold.

[0006] Optionally, increasing the discharge cutoff voltage includes: determining the amount of increase in the discharge cutoff voltage based on the amount of silicon-carbon doping in the negative electrode active material of the electrochemical device and the mass percentage of silicon in the silicon-carbon material; and increasing the discharge cutoff voltage according to the amount of increase in the discharge cutoff voltage.

[0007] Optionally, the range of the increase in the discharge cutoff voltage is 0.01V to 0.5V.

[0008] Optionally, the values ​​of the first thickness change rate threshold and the second thickness change rate threshold are both determined based on the number of voltage boosts of the electrochemical device and the theoretical expansion rate of the negative electrode active material.

[0009] Optionally, the theoretical expansion rate of the negative electrode active material is determined based on the amount of silicon-carbon mixed in the negative electrode active material, the tap density of the silicon-carbon material, and the mass percentage of silicon in the silicon-carbon material.

[0010] Optionally, the charging cut-off voltage ranges from 4.4V to 4.7V, and the discharging cut-off voltage ranges from 2.2V to 3.7V.

[0011] Optionally, the method further includes: stopping the charge-discharge cycle of the electrochemical device when the number of cycles of the electrochemical device is not less than 1000 or the capacity retention rate of the electrochemical device is not greater than 80%.

[0012] According to another aspect of the present invention, an electrochemical device is provided, comprising: a negative electrode active material of the electrochemical device comprising a first active material and a second active material; the specific capacity of the first active material being less than that of the second active material; the discharge operating voltage range of the first active material comprising a first voltage range not greater than the upper limit of the discharge operating voltage of the second active material; when the thickness change rate of the electrochemical device after multiple charge-discharge cycles is less than a first thickness change rate threshold, the electrochemical device is charged and discharged according to the charging cut-off voltage and the discharging cut-off voltage of the electrochemical device; when the thickness change rate of the electrochemical device after multiple charge-discharge cycles is greater than or equal to the first thickness change rate threshold and less than a second thickness change rate threshold, the discharging cut-off voltage is increased, and the electrochemical device is charged and discharged according to the charging cut-off voltage and the increased discharging cut-off voltage; when the thickness change rate of the electrochemical device after multiple charge-discharge cycles is greater than or equal to the second thickness change rate threshold, the discharging cut-off voltage is increased again, and the electrochemical device is charged and discharged according to the charging cut-off voltage and the increased discharging cut-off voltage; wherein the first thickness change rate threshold is less than the second thickness change rate threshold.

[0013] Optionally, the first active material includes graphite, and the second active material includes silicon or silicon-carbon material; in the negative electrode active material, the amount of silicon-carbon mixed ranges from 1% to 99%, and the tap density of the silicon-carbon material ranges from 1.1 to 2.3 g / cm³. 3 The mass percentage of silicon in the silicon-carbon material ranges from 1% to 99%.

[0014] According to another aspect of the present invention, an electronic device is provided, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the electrochemical device charging and discharging method described above.

[0015] In this embodiment of the invention, by obtaining the thickness change rate of the electrochemical device after multiple charge-discharge cycles, when the thickness change rate is less than a first thickness change rate threshold, charging and discharging are performed according to conventional charging and discharging cutoff voltages. If the thickness change rate reaches or exceeds the first thickness change rate threshold, it indicates that a significant volume expansion problem has begun to appear. By increasing the discharge cutoff voltage, the degree of lithium intercalation of the negative electrode active material is appropriately reduced, thereby reducing the volume expansion effect generated by the negative electrode active material during lithium intercalation. Similarly, after one voltage increase, when the thickness change rate further increases and reaches a second thickness change rate threshold, it indicates that the volume expansion problem has intensified. The degree of lithium intercalation of the negative electrode active material is further reduced to suppress the volume expansion effect generated by the negative electrode active material during lithium intercalation. This solves the technical problem of decreased cycle performance or even failure of the electrochemical device due to volume expansion during charge-discharge cycles, achieving the technical effect of suppressing the volume expansion effect of the electrochemical device and improving the cycle performance of the electrochemical device. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0017] Figure 1 A flowchart of the charging and discharging method of the electrochemical device provided in the embodiments of the present invention;

[0018] Figure 2 The graph shows the relationship between the capacity retention rate of the batteries in Examples 1-2 and Comparative Example 1 and the number of cycles.

[0019] Figure 3 The graph shows the relationship between the thickness expansion rate of the batteries in Examples 1-2 and Comparative Example 1 and the number of cycles.

[0020] Figure 4 A schematic diagram showing the internal structure of the electrochemical device, battery thickness gauge, and computer provided by the present invention, and the relationship between them.

[0021] Figure 5 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0022] Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While some embodiments of the invention are shown in the drawings, it should be understood that embodiments of the invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the embodiments of the invention. It should be understood that the accompanying drawings and embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the invention.

[0023] According to one aspect of the present invention, a method for charging and discharging an electrochemical device is provided. Figure 1 A flowchart of the charging and discharging method of the electrochemical device provided in the embodiments of the present invention is shown below. Figure 1 As shown, the method includes the following steps:

[0024] Step S102: Obtain the thickness change rate of the electrochemical device after multiple charge-discharge cycles;

[0025] Among them, the thickness change rate is an indicator reflecting the degree of volume expansion of the electrochemical device; the charge-discharge cycle refers to one repeated process of charging and discharging the electrochemical device under specified conditions.

[0026] Step S104: When the thickness change rate is less than the first thickness change rate threshold, the electrochemical device is charged and discharged according to the charging cut-off voltage and discharging cut-off voltage of the electrochemical device.

[0027] Step S106: When the thickness change rate is greater than or equal to the first thickness change rate threshold and less than the second thickness change rate threshold, the discharge cutoff voltage is increased, and the electrochemical device is charged and discharged according to the charging cutoff voltage and the increased discharge cutoff voltage.

[0028] Step S108: When the thickness change rate is greater than or equal to the second thickness change rate threshold, the discharge cutoff voltage is increased again, and the electrochemical device is charged and discharged according to the charging cutoff voltage and the increased discharge cutoff voltage.

[0029] Among them, the first thickness change rate threshold is less than the second thickness change rate threshold.

[0030] In this embodiment of the invention, the method obtains the thickness change rate of the electrochemical device after multiple charge-discharge cycles. When the thickness change rate is less than a first thickness change rate threshold, charging and discharging are performed according to conventional charging and discharging cutoff voltages. If the thickness change rate reaches or exceeds the first thickness change rate threshold, it indicates that a significant volume expansion problem has begun to appear. By increasing the discharge cutoff voltage, the degree of lithium intercalation of the negative electrode active material is appropriately reduced, thereby reducing the volume expansion effect generated by the negative electrode active material during lithium intercalation. Similarly, after one voltage increase, when the thickness change rate further increases and reaches a second thickness change rate threshold, it indicates that the volume expansion problem has intensified. The degree of lithium intercalation of the negative electrode active material is further reduced to suppress the volume expansion effect generated by the negative electrode active material during lithium intercalation. This solves the technical problem of decreased cycle performance or even failure of the electrochemical device due to volume expansion during charge-discharge cycles, achieving the technical effect of suppressing the volume expansion effect of the electrochemical device and improving the cycle performance of the electrochemical device.

[0031] It should be noted that the electrochemical devices involved in the embodiments of the present invention include, but are not limited to, lithium-ion batteries, sodium-ion batteries, etc.

[0032] As an optional embodiment, obtaining the thickness change rate of the electrochemical device after multiple charge-discharge cycles includes: obtaining the initial battery thickness before the electrochemical device undergoes charge-discharge cycles and the current battery thickness after the electrochemical device undergoes multiple charge-discharge cycles; calculating the difference between the current battery thickness and the initial battery thickness to obtain the thickness difference of the electrochemical device; and calculating the ratio between the thickness difference of the electrochemical device and the initial battery thickness to obtain the thickness change rate.

[0033] Optionally, before performing charge-discharge cycles on the electrochemical device, the battery thickness of the electrochemical device is first accurately measured and recorded; this value is the initial battery thickness. Then, the electrochemical device is subjected to multiple charge-discharge cycles according to predetermined charging and discharging cutoff voltages. This process may cause changes in the internal structure of the electrochemical device, thereby affecting the battery thickness. After completing the predetermined number of charge-discharge cycles, the battery thickness of the electrochemical device is accurately measured again; the obtained value is the current battery thickness. Finally, the current battery thickness is subtracted from the initial battery thickness to obtain the thickness difference of the electrochemical device. The thickness difference is divided by the initial battery thickness and then multiplied by 100% (or converted to decimal form) to obtain the thickness change rate of the electrochemical device after multiple charge-discharge cycles. This value can reflect the volume stability of the electrochemical device during the cycling process.

[0034] Optionally, a battery thickness gauge can be used to measure the initial battery thickness and the current battery thickness of the electrochemical device.

[0035] It should be noted that the thickness gauge needs to be calibrated before measurement to ensure the accuracy of the results. During measurement, ensure the thickness gauge is perpendicular to the surface of the electrochemical device, avoiding tilting or offset which could lead to inaccurate results. The probe of the thickness gauge should avoid contact with the surface of the electrochemical device to prevent probe damage and inaccurate results. After the test, the initial battery thickness and current battery thickness of the electrochemical device are transmitted to the data processing equipment to calculate the thickness change rate of the electrochemical device after multiple charge-discharge cycles.

[0036] Optionally, the relationship between the above-mentioned thickness change rate and the current thickness of the electrochemical device and the initial thickness of the electrochemical device is expressed as follows:

[0037] ΔT=(T n -T0) / T0

[0038] Where ΔT represents the thickness change rate, T n T0 represents the current battery thickness, while T0 represents the initial battery thickness.

[0039] As an optional embodiment, increasing the discharge cutoff voltage includes: determining the amount of increase in the discharge cutoff voltage based on the amount of silicon-carbon doping in the negative electrode active material of the electrochemical device and the mass percentage of silicon in the silicon-carbon material; and increasing the discharge cutoff voltage according to the amount of increase in the discharge cutoff voltage.

[0040] Optionally, the relationship between the increase in the discharge cutoff voltage and the amount of silicon-carbon doping in the negative electrode active material of the electrochemical device, and the mass percentage of silicon in the silicon-carbon material, is expressed as follows:

[0041] ΔV = 0.05 + 3ω 硅碳 ω 硅

[0042] Where ΔV represents the increase in discharge cutoff voltage, ω 硅碳 ω represents the amount of silicon-carbon incorporated into the negative electrode active material of an electrochemical device. 硅 This indicates the mass percentage of silicon in silicon-carbon materials.

[0043] It should be noted that when the silicon content in the negative electrode active material is low, a lower increase in the discharge cutoff voltage should be selected to ensure that the active material in the negative electrode active material fully utilizes its specific capacity; when the silicon content in the negative electrode active material is high, the increase in the discharge cutoff voltage should be appropriately increased to reduce the degree of lithium intercalation in the negative electrode active material, thereby reducing the volume expansion effect generated by the negative electrode active material during the lithium intercalation process.

[0044] As an optional embodiment, the range of the above-mentioned increase in discharge cutoff voltage is 0.01V to 0.5V.

[0045] Regarding the increase in discharge cutoff voltage, if the increase is set too high, it will hinder the release of energy from the electrode material in the electrochemical device; if the increase is set too low, frequent increases in discharge cutoff voltage may be necessary, thus limiting the improvement of the cycle stability and the suppression of thickness expansion in the electrochemical device. Therefore, in this embodiment of the invention, setting the increase in discharge cutoff voltage within the range of 0.01V to 0.5V effectively avoids the aforementioned problems.

[0046] As an optional embodiment, the values ​​of the first thickness change rate threshold and the second thickness change rate threshold are both determined based on the number of voltage boosts of the electrochemical device and the theoretical expansion rate of the negative electrode active material.

[0047] Optionally, the thickness change rate threshold of the electrochemical device includes a first thickness change rate threshold and a second thickness change rate threshold, i.e., the thickness change rate threshold depends on the number of voltage boosts of the electrochemical device and the theoretical expansion rate of the negative electrode active material.

[0048] In embodiments of the present invention, as battery usage time increases and charge-discharge cycles accumulate, battery performance gradually changes, especially the expansion characteristics of the negative electrode active material. This method combines the actual situation of the electrochemical device (number of voltage boosts m) with the inherent properties of the material (theoretical expansion rate of the negative electrode active material) to provide corresponding thickness change rate thresholds for electrochemical devices with different battery types and material characteristics, forming a dynamic adjustment charge-discharge strategy to ensure good performance even during the aging process of the electrochemical device, thereby improving its performance and lifespan.

[0049] Optionally, the relationship between the aforementioned thickness change rate threshold and the number of voltage boosts in the electrochemical device and the theoretical expansion rate of the negative electrode active material is expressed as follows:

[0050] ΔT m+1 = (0.8 + 0.1m)ΔV 负极

[0051] Where m represents the number of voltage boosts in the electrochemical device, ΔV 负极 The value represents the theoretical expansion rate of the negative electrode active material, and 0.8 + 0.1 m represents the degree of lithium intercalation of the negative electrode active material during charging.

[0052] In the embodiments of the present invention, the thickness change rate threshold is dynamically set according to the actual situation of the electrochemical device (number of voltage boosts m) and the inherent properties of the material (theoretical expansion rate of the negative electrode active material). This allows for timely response to changes in battery state and prevents performance degradation caused by excessive expansion. In addition, as m increases, the "0.8+0.1m" portion gradually increases, which means that as the electrochemical device undergoes more voltage boosts (i.e., more charge-discharge cycles and expansion control interventions), the control over the degree of lithium intercalation in the negative electrode active material becomes more stringent. This allows for a more precise balance between the battery's energy storage performance and cycle life, avoiding excessive intervention in the early stages or insufficient intervention in the later stages.

[0053] For example, when the thickness change rate of the electrochemical device is greater than or equal to a first thickness change rate threshold (ΔT1 = ...

[0054] 0.8ΔV 负极 At this point, the lithium intercalation degree of the negative electrode active material reaches 80%. The discharge cutoff voltage of the electrochemical device is then increased from the first discharge cutoff voltage to the second discharge cutoff voltage. By increasing the discharge cutoff voltage, the lithium intercalation degree of the negative electrode active material is appropriately reduced, thereby minimizing the volume expansion effect generated during lithium intercalation. Similarly, after one voltage increase, when the thickness change rate of the electrochemical device is greater than or equal to the second thickness change rate threshold (ΔT2 = ...), ...

[0055] 0.9ΔV 负极 At this point, the lithium intercalation degree of the negative electrode active material reaches 90%, and the discharge cutoff voltage of the electrochemical device is increased from the second discharge cutoff voltage to the third discharge cutoff voltage, further reducing the lithium intercalation degree of the negative electrode active material and suppressing the volume expansion effect generated by the negative electrode active material during the lithium intercalation process.

[0056] As an optional embodiment, the theoretical expansion rate of the negative electrode active material is determined based on the amount of silicon-carbon mixed in the negative electrode active material, the tap density of the silicon-carbon material, and the mass percentage of silicon in the silicon-carbon material.

[0057] For silicon-carbon materials, during the charging process of the electrochemical device, lithium ions are inserted into the silicon particles and undergo an alloying reaction with silicon to form LiSi and Li. 12 Si7, Li 13 Si4 and Li 22 Compounds such as Si5 exhibit significant volume expansion, reaching approximately 365%, which can easily lead to silicon particle breakage and failure. Therefore, in practical applications, silicon-carbon materials are usually used in combination with graphite. During the charging process of the electrochemical device, lithium ions intercalate between graphite layers to form LiC6, with a volume expansion rate of only 10%, which can effectively suppress the volume expansion effect of silicon during lithium intercalation.

[0058] Optionally, the relationship between the theoretical expansion rate of the above-mentioned negative electrode active material and the amount of silicon-carbon doping in the negative electrode active material, the tap density of the silicon-carbon material, and the mass percentage of silicon in the silicon-carbon material is expressed as follows:

[0059]

[0060] Where, ΔV 负极 ω represents the theoretical expansion rate of the negative electrode active material. 硅碳 ρ represents the amount of silicon and carbon incorporated into the negative electrode active material. 硅碳 The tap density of silicon-carbon materials is represented by α, which indicates the complete lithium intercalation of single-crystal silicon into Li at room temperature. 15 The volume change rate of Si4, ω 硅 ρ represents the mass percentage of silicon in silicon-carbon materials. 硅 ρ represents the tap density of monocrystalline silicon. 碳 ΔV represents the tap density of the porous carbon matrix in silicon-carbon materials. 石墨 This represents the theoretical expansion rate of graphite.

[0061] Among the parameters mentioned above, for the same negative electrode active material, Si-Li 15 The volume change rate α of Si4 and the tap density ρ of single-crystal silicon 硅 ρ, tap density of porous carbon matrix 碳 The theoretical expansion rate ΔV of graphite 石墨 All values ​​are fixed. Therefore, the theoretical expansion rate of the negative electrode active material depends on the amount of silicon and carbon mixed in the negative electrode active material, ω. 硅碳 ρ, tap density of silicon-carbon materials 硅碳 And the mass percentage of silicon in silicon-carbon materials ω 硅 .

[0062] In the embodiments of the present invention, by comprehensively considering the specific composition of the silicon-carbon composite material (such as silicon content, tap density, etc.), the theoretical expansion rate of the negative electrode active material during the charging and discharging process can be accurately predicted, which helps to avoid potential problems caused by volume expansion in advance.

[0063] As an optional embodiment, the range of the charging cut-off voltage is 4.4V to 4.7V; the range of the discharging cut-off voltage is 2.2V to 3.7V.

[0064] It should be noted that if the charging cut-off voltage is set too high, it will hinder the release of energy from the electrode materials in the electrochemical device; if the charging cut-off voltage is set too low, the improvement in the cycle performance of the electrochemical device will be insignificant. Therefore, in this invention, setting the charging cut-off voltage within the range of 4.4V to 4.7V can effectively avoid the aforementioned problems.

[0065] As an optional embodiment, the above method further includes: stopping the charge-discharge cycle of the electrochemical device when the number of cycles of the electrochemical device is not less than 1000 or the capacity retention rate of the electrochemical device is not greater than 80%.

[0066] In actual testing, to evaluate the long-term performance and lifespan of electrochemical devices, further charge-discharge cycles are stopped after the device has completed at least 1000 cycles. This is because 1000 cycles often reflects most of the aging process of the electrochemical device under normal operating conditions. Additionally, the usable capacity of the electrochemical device tends to gradually decrease with each charge-discharge cycle. When the capacity of the electrochemical device falls below 80% of its initial capacity, it is generally considered that the device's performance has significantly degraded, and charge-discharge cycle testing is also stopped.

[0067] The following comparisons of Examples 1 to 7 illustrate the advantages of the electrochemical device charging and discharging method provided by the present invention.

[0068] Example 1

[0069] The electrochemical device in this embodiment is a lithium-ion battery. The negative electrode active material is a blend of 5% silicon-carbon and 95% graphite. The silicon content in the silicon-carbon material is 33.7%. The specific charging and discharging steps of the battery are as follows:

[0070] 1. Before charging begins, use a battery thickness gauge to measure and record the initial battery thickness.

[0071] 2. Charge and discharge within the range of charging cutoff voltage and first discharge cutoff voltage (2.8V), and measure the current battery thickness after every 10 cycles;

[0072] 3. When the battery thickness change rate is greater than the first thickness change rate threshold (10.0%), the first discharge cutoff voltage is increased to the second discharge cutoff voltage (2.9V); otherwise, the charging and discharging continues at the first discharge cutoff voltage.

[0073] 4. When the battery thickness change rate is greater than the second thickness change rate threshold (11.3%), the second discharge cutoff voltage is increased to the third discharge cutoff voltage (3.0V); otherwise, the charging and discharging continues at the second discharge cutoff voltage.

[0074] 5. Stop charging and discharging when the battery cycle count exceeds 1000 cycles or the capacity retention rate is less than 80%.

[0075] Example 2

[0076] The electrochemical device in this embodiment is a lithium-ion battery. The negative electrode active material is a blend of 5% silicon-carbon and 95% graphite. The silicon content in the silicon-carbon material is 33.7%. The specific charging and discharging steps of the battery are as follows:

[0077] 1. Before charging begins, use a battery thickness gauge to measure and record the initial battery thickness.

[0078] 2. Charge and discharge within the range of charging cutoff voltage and first discharge cutoff voltage (2.8V), and measure the current battery thickness after every 10 cycles;

[0079] 3. When the battery thickness change rate is greater than 11.3%, the first discharge cutoff voltage is increased to 3.0V; otherwise, the charging and discharging continues at the first discharge cutoff voltage.

[0080] 4. Stop charging and discharging when the battery cycle count exceeds 1000 cycles or the capacity retention rate is less than 80%.

[0081] Comparative Example 1

[0082] The electrochemical device in this comparative example is a lithium-ion battery. The negative electrode active material is a blend of 5% silicon-carbon and 95% graphite. The silicon content in the silicon-carbon material is 33.7%. The specific charging and discharging steps of the battery are as follows:

[0083] 1. Before charging begins, use a battery thickness gauge to measure and record the initial battery thickness.

[0084] 2. Charge and discharge within the range of charging cutoff voltage and first discharge cutoff voltage (2.8V), and measure the current battery thickness after every 10 cycles;

[0085] 3. Stop charging and discharging when the battery cycle count is greater than 1000 cycles or the capacity retention rate is less than 80%.

[0086] Example 3

[0087] The electrochemical device in this embodiment is a lithium-ion battery. The negative electrode active material is a blend of 7% silicon-carbon and 93% graphite. The silicon content in the silicon-carbon material is 33.7%. The specific charging and discharging steps of the battery are as follows:

[0088] 1. Before charging begins, use a battery thickness gauge to measure and record the initial battery thickness.

[0089] 2. Charge and discharge within the range of charging cutoff voltage and first discharge cutoff voltage (2.8V), and measure the current battery thickness after every 10 cycles;

[0090] 3. When the battery thickness change rate is greater than the first thickness change rate threshold (10.9%), the first discharge cutoff voltage is increased to the second discharge cutoff voltage (2.9V); otherwise, the charging and discharging continues at the first discharge cutoff voltage.

[0091] 4. When the battery thickness change rate is greater than the second thickness change rate threshold (12.2%), the second discharge cutoff voltage is increased to the third discharge cutoff voltage (3.0V); otherwise, the charging and discharging continues at the second discharge cutoff voltage.

[0092] 5. Stop charging and discharging when the battery cycle count exceeds 1000 cycles or the capacity retention rate is less than 80%.

[0093] Comparative Example 2

[0094] The electrochemical device in this comparative example is a lithium-ion battery. The negative electrode active material is a blend of 7% silicon-carbon and 93% graphite. The silicon content in the silicon-carbon material is 33.7%. The specific charging and discharging steps of the battery are as follows:

[0095] 1. Before charging begins, use a battery thickness gauge to measure and record the initial battery thickness.

[0096] 2. Charge and discharge within the range of charging cutoff voltage and first discharge cutoff voltage (2.8V), and measure the current battery thickness after every 10 cycles;

[0097] 3. Stop charging and discharging when the battery cycle count is greater than 1000 cycles or the capacity retention rate is less than 80%.

[0098] Example 4

[0099] The electrochemical device in this embodiment is a lithium-ion battery. The negative electrode active material is a blend of 5% silicon-carbon and 95% graphite. The silicon content in the silicon-carbon material is 47.1%. The specific charging and discharging steps of the battery are as follows:

[0100] 1. Before charging begins, use a battery thickness gauge to measure and record the initial battery thickness.

[0101] 2. Charge and discharge within the range of charging cutoff voltage and first discharge cutoff voltage (2.8V), and measure the current battery thickness after every 10 cycles;

[0102] 3. When the battery thickness change rate is greater than the first thickness change rate threshold (11.1%), the first discharge cutoff voltage is increased to the second discharge cutoff voltage (2.9V); otherwise, the charging and discharging continues at the first discharge cutoff voltage.

[0103] 4. When the battery thickness change rate is greater than the second thickness change rate threshold (12.5%), the second discharge cutoff voltage is increased to the third discharge cutoff voltage (3.0V); otherwise, the charging and discharging continues at the second discharge cutoff voltage.

[0104] 5. Stop charging and discharging when the battery cycle count exceeds 1000 cycles or the capacity retention rate is less than 80%.

[0105] Comparative Example 3

[0106] The electrochemical device in this comparative example is a lithium-ion battery. The negative electrode active material is a blend of 5% silicon-carbon and 95% graphite. The silicon content in the silicon-carbon material is 47.1%. The specific charging and discharging steps of the battery are as follows:

[0107] 1. Before charging begins, use a battery thickness gauge to measure and record the initial battery thickness.

[0108] 2. Charge and discharge within the range of charging cutoff voltage and first discharge cutoff voltage (2.8V), and measure the current battery thickness after every 10 cycles;

[0109] 3. Stop charging and discharging when the battery cycle count is greater than 1000 cycles or the capacity retention rate is less than 80%.

[0110] like Figure 2 , Figure 3 As shown, within the first 600 cycles, Examples 1 and 2, and Comparative Example 1 exhibited comparable capacity retention and thickness expansion rates. When the first thickness change rate threshold (0.8ΔV) was reached... 负极 When the first discharge cutoff voltage in Example 1 was increased to the second discharge cutoff voltage (=10%), the capacity retention rate and thickness expansion rate were improved. When the second thickness change rate threshold (0.9ΔV) was reached... 负极 When the discharge cutoff voltage was increased from the second to the third discharge cutoff voltage (=11.3%), the capacity retention and thickness expansion rate of the battery were further improved, showing a significant improvement in cycle performance compared to Comparative Example 1 without the voltage increase operation. In contrast, although the discharge cutoff voltage increase was the same for Example 2 and Example 1, Example 2, which only underwent one voltage increase operation (i.e., increasing the discharge cutoff voltage), showed limited improvement in capacity retention and thickness expansion rate compared to Example 1. When the battery thickness change rate reached 0.9ΔV... 负极 When the lithium insertion depth of the negative electrode active material is relatively deep and the irreversible capacity is also larger, it is difficult to reduce the capacity reduction and expansion caused by the irreversible capacity when the discharge cutoff voltage is increased.

[0111] Table 1

[0112]

[0113] Table 1 shows the effects of different silicon-carbon mixing amounts and silicon content on the thickness change rate thresholds of the negative electrode active materials and the effect of pressure rise on the capacity retention rate and expansion rate of the electrochemical energy storage devices in Examples 1-4 and Comparative Examples 1-3. Based on the analysis of Examples 1-4 and Comparative Examples 1-3 in conjunction with Table 1, the following conclusions can be drawn:

[0114] As can be seen from Examples 1, 3, and 4, the expansion rate of the battery increases when the silicon-carbon doping content in the negative electrode active material and / or the silicon content in the silicon-carbon material increases. According to the thickness change rate threshold calculation formula provided in this embodiment of the invention, increasing the silicon-carbon doping content in the negative electrode active material and / or the silicon content in the silicon-carbon material corresponds to a higher thickness change rate threshold. Therefore, appropriately increasing the thickness change rate threshold of the battery allows it to exert more capacity before increasing the discharge cutoff voltage, thereby improving the battery's energy density.

[0115] As can be seen from Examples 1-2 and Comparative Example 1, Examples 3 and Comparative Example 2, and Examples 4 and Comparative Example 3, the capacity retention rate and thickness expansion rate of the battery are improved after using the charging and discharging method provided by the present invention. This indicates that the charging and discharging method provided by the present invention has universality and can effectively improve the cycle performance of silicon-carbon anode lithium-ion batteries.

[0116] In summary, the charging and discharging method provided by this invention, when the thickness change rate is less than the first thickness change rate threshold, performs charging and discharging according to the conventional charging cut-off voltage and discharging cut-off voltage; if the thickness change rate reaches or exceeds the first thickness change rate threshold, it indicates that a significant volume expansion problem begins to appear. By increasing the discharging cut-off voltage, the degree of lithium intercalation of the negative electrode active material is appropriately reduced, thereby reducing the volume expansion effect generated by the negative electrode active material during lithium intercalation; similarly, after one voltage increase, when the thickness change rate further increases and reaches the second thickness change rate threshold, it indicates that the volume expansion problem is aggravated. Further reducing the degree of lithium intercalation of the negative electrode active material suppresses the volume expansion effect generated by the negative electrode active material during lithium intercalation, thereby solving the technical problem of decreased cycle performance or even failure of electrochemical devices due to volume expansion during charge and discharge cycles, achieving the technical effect of suppressing the volume expansion effect of electrochemical devices and improving the cycle performance of electrochemical devices.

[0117] According to another aspect of the present invention, an electrochemical device is provided. The electrochemical device includes: a negative electrode active material comprising a first active material and a second active material; the specific capacity of the first active material is less than that of the second active material; and the discharge operating voltage range of the first active material includes a first voltage range not greater than the upper limit of the discharge operating voltage of the second active material.

[0118] When the thickness change rate of the electrochemical device after multiple charge-discharge cycles is less than the first thickness change rate threshold, the electrochemical device is charged and discharged according to the charging cut-off voltage and discharging cut-off voltage of the electrochemical device.

[0119] When the thickness change rate of the electrochemical device after multiple charge-discharge cycles is greater than or equal to the first thickness change rate threshold and less than the second thickness change rate threshold, the discharge cut-off voltage is increased, and the electrochemical device is charged and discharged according to the charging cut-off voltage and the increased discharge cut-off voltage.

[0120] When the thickness change rate of the electrochemical device after multiple charge-discharge cycles is greater than or equal to the second thickness change rate threshold, the discharge cutoff voltage is increased again, and the electrochemical device is charged and discharged according to the charging cutoff voltage and the increased discharge cutoff voltage; wherein, the first thickness change rate threshold is less than the second thickness change rate threshold.

[0121] The upper limit of the discharge working voltage of the first active material is higher than the upper limit of the discharge working voltage of the second active material.

[0122] In this embodiment of the invention, the electrochemical device performs charging and discharging according to conventional charging and discharging cutoff voltages when the thickness change rate is less than a first thickness change rate threshold. If the thickness change rate reaches or exceeds the first thickness change rate threshold, it indicates that a significant volume expansion problem has begun to occur. By increasing the discharge cutoff voltage, the degree of lithium intercalation of the negative electrode active material is appropriately reduced, thereby reducing the volume expansion effect generated by the negative electrode active material during lithium intercalation. Similarly, after one voltage increase, when the thickness change rate further increases and reaches a second thickness change rate threshold, it indicates that the volume expansion problem has intensified. The degree of lithium intercalation of the negative electrode active material is further reduced to suppress the volume expansion effect generated by the negative electrode active material during lithium intercalation. This solves the technical problem of decreased cycle performance or even failure of the electrochemical device due to volume expansion during charge and discharge cycles, achieving the technical effect of suppressing the volume expansion effect of the electrochemical device and improving the cycle performance of the electrochemical device.

[0123] In embodiments of the present invention, such as Figure 4 As shown, the electrochemical device can also communicate with a battery thickness gauge and a computer. The battery thickness gauge mainly consists of a measuring fixture and a data acquisition unit, which is used to measure the initial and current battery thickness of the electrochemical device and provide the collected thickness data to the computer and / or the electrochemical device (which integrates a memory and a processor, etc.). In addition, the computer mainly consists of a memory and a processor, which is used to control the operation of the battery thickness gauge and the electrochemical device.

[0124] As an optional embodiment, the first active material includes graphite, and the second active material includes silicon or silicon-carbon material; in the negative electrode active material, the doping amount of silicon-carbon ranges from 1% to 99%, and the tap density of the silicon-carbon material ranges from 1.1 to 2.3 g / cm³. 3 The mass percentage of silicon in silicon-carbon materials ranges from 1% to 99%.

[0125] Optionally, the values ​​of the silicon-carbon blending amount mentioned above include, but are not limited to: 3%, 5%, 7%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%.

[0126] Low doping (e.g., 3%–10%): Lower silicon content can reduce the volume expansion effect during charge and discharge, and improve the cycle stability and structural stability of the battery, but may sacrifice some energy density.

[0127] Medium blending content (e.g., 20%–50%): A moderate silicon content can significantly improve the energy density of the battery while maintaining good cycle performance. Optimizing the binder and electrolyte can effectively alleviate the problem of silicon particle breakage and shedding.

[0128] High doping levels (e.g., 60%–90%): Extremely high silicon content can achieve higher theoretical specific capacity, but it also poses a great challenge to the structural stability and cycle life of the battery, requiring advanced material design and technology to overcome the problem of huge volume changes.

[0129] Optionally, the tap density of the aforementioned silicon carbide may include, but is not limited to, 1.5 g / cm³. 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 2.0g / cm 3 2.1g / cm 3 2.2g / cm 3 .

[0130] Low tap density (e.g., 1.5–1.8 g / cm³) 3 A lower tap density means more voids inside the material, which may reduce the energy density of the battery, but it helps the electrolyte to penetrate and improves the efficiency of the electrochemical reaction.

[0131] High tap density (e.g., 1.9–2.2 g / cm³) 3 Increasing the tap density can increase the energy density of the battery, allowing more active materials to be encapsulated within the same volume. However, care must be taken not to over-compact the material, which could obstruct the electronic conduction path or generate excessive stress within the material.

[0132] Optionally, the mass percentage of silicon in the above-mentioned silicon-carbon materials may include, but is not limited to, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%.

[0133] Low silicon mass percentage (e.g., 10%–30%) tends to have better cycle stability and processing performance, making it suitable for applications requiring long life and stability.

[0134] High silicon mass percentage (e.g., 40%–90%): Applications that pursue high energy density require more complex battery management systems and material modification technologies to overcome the volume expansion problem of silicon and ensure battery safety and cycle performance.

[0135] In embodiments of the present invention, by adjusting the amount of silicon, tap density, and mass percentage of silicon in the silicon-carbon composite material, a trade-off can be made between energy density, cycle stability, and processing performance to meet the needs of different application scenarios.

[0136] According to another aspect of the present invention, an electronic device is provided, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the electrochemical device charging and discharging method of the present invention.

[0137] According to another aspect of the present invention, a computer-readable storage medium is provided having a computer program / instructions stored thereon, which, when executed by a processor, implements the electrochemical device charging and discharging method of the present invention.

[0138] According to another aspect of the present invention, a computer program product is provided, including a computer program / instructions that, when executed by a processor, implement the electrochemical device charging and discharging method of the present invention.

[0139] refer to Figure 5 The present invention will now describe a structural block diagram of an electronic device that can serve as a server or client in embodiments of the present invention, which is an example of a hardware device that can be applied to various aspects of the present invention. The electronic device is intended to represent various forms of digital electronic computer devices, such as laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device can also represent various forms of mobile devices, such as personal digital processors, cellular phones, smartphones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely illustrative and are not intended to limit the implementation of the invention described and / or claimed herein.

[0140] like Figure 5As shown, the electronic device includes a computing unit 501, which can perform various appropriate actions and processes based on a computer program stored in a read-only memory (ROM) 502 or a computer program loaded from a storage unit 508 into a random access memory (RAM) 503. The RAM 503 may also store various programs and data required for the operation of the electronic device. The computing unit 501, ROM 502, and RAM 503 are interconnected via a bus 504. An input / output (I / O) interface 505 is also connected to the bus 504.

[0141] Multiple components in the electronic device are connected to I / O interface 505, including: input unit 506, output unit 507, storage unit 508, and communication unit 509. Input unit 506 can be any type of device capable of inputting information into the electronic device. Input unit 506 can receive input digital or character information and generate key signal inputs related to user settings and / or function control of the electronic device. Output unit 507 can be any type of device capable of presenting information and may include, but is not limited to, a display, speaker, video / audio output terminal, vibrator, and / or printer. Storage unit 508 may include, but is not limited to, disks and optical discs. Communication unit 509 allows the electronic device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunications networks, and may include, but is not limited to, modems, network cards, infrared communication devices, and wireless communication transceivers, such as Bluetooth devices, WiFi devices, WiMax devices, cellular communication devices, and / or the like.

[0142] The computing unit 501 can be a variety of general-purpose and / or special-purpose processing components with processing and computing capabilities. Some examples of the computing unit 501 include, but are not limited to, CPUs, graphics processing units (GPUs), various special-purpose artificial intelligence (AI) computing units, various computing units running machine learning model algorithms, digital signal processors (DSPs), and any suitable processor, controller, microcontroller, etc. The computing unit 501 performs the various methods and processes described above. For example, in some embodiments, the method embodiments of the present invention can be implemented as a computer program tangibly contained in a machine-readable medium, such as storage unit 508. In some embodiments, part or all of the computer program can be loaded and / or installed on an electronic device via ROM 502 and / or communication unit 509. In some embodiments, the computing unit 501 can be configured to perform the methods described above by any other suitable means (e.g., by means of firmware).

[0143] Computer programs for implementing the methods of embodiments of the present invention may be written in any combination of one or more programming languages. These computer programs may be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus, such that when executed by the processor or controller, the computer programs cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The computer programs may be executed entirely on a machine, partially on a machine, or as a standalone software package, partially on a machine and partially on a remote machine, or entirely on a remote machine or server.

[0144] In the context of embodiments of the present invention, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. A machine-readable signal medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0145] It should be noted that the term "comprising" and its variations used in the embodiments of the present invention are open-ended, meaning "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". The modifications of "one" and "multiple" mentioned in the embodiments of the present invention are illustrative and not restrictive. Those skilled in the art should understand that, unless explicitly indicated otherwise in the context, they should be understood as "one or more".

[0146] The steps described in the method embodiments provided by this invention can be performed in different orders and / or in parallel. Furthermore, the method embodiments may include additional steps and / or omit the steps shown. The scope of protection of this invention is not limited in this respect.

[0147] The term "embodiment" in this specification refers to a specific feature, structure, or characteristic described in connection with an embodiment that may be included in at least one embodiment of the invention. The appearance of this phrase in various places in the specification does not necessarily imply the same embodiment, nor does it imply independence or alternativeity from other embodiments. The various embodiments in this specification are described in a related manner, with reference to each other for similar or identical parts. In particular, for apparatus, device, and system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, and relevant details are referred to in the description of the method embodiments.

[0148] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of patent protection. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A charging and discharging method for an electrochemical device, characterized in that, include: The thickness change rate of the electrochemical device after multiple charge-discharge cycles was obtained. When the thickness change rate is less than the first thickness change rate threshold, the electrochemical device is charged and discharged according to the charging cut-off voltage and discharging cut-off voltage of the electrochemical device. When the thickness change rate is greater than or equal to the first thickness change rate threshold and less than the second thickness change rate threshold, the discharge cutoff voltage is increased, and the electrochemical device is charged and discharged according to the charging cutoff voltage and the increased discharge cutoff voltage. When the thickness change rate is greater than or equal to the second thickness change rate threshold, the discharge cutoff voltage is increased again, and the electrochemical device is charged and discharged according to the charging cutoff voltage and the increased discharge cutoff voltage. Wherein, the first thickness change rate threshold is less than the second thickness change rate threshold; The relationship between the thickness change rate and the current thickness of the electrochemical device and the initial thickness of the electrochemical device is expressed as follows: in, This represents the rate of change of thickness. This indicates the thickness of the current electrochemical device. This indicates the initial thickness of the electrochemical device; Increasing the discharge cutoff voltage includes: determining the amount of increase in the discharge cutoff voltage based on the amount of silicon-carbon material mixed in the negative electrode active material of the electrochemical device and the mass percentage of silicon in the silicon-carbon material; and increasing the discharge cutoff voltage according to the amount of increase in the discharge cutoff voltage.

2. The method according to claim 1, characterized in that, The range of the increase in the discharge cutoff voltage is 0.01V to 0.5V.

3. The method according to claim 1, characterized in that, The values ​​of the first thickness change rate threshold and the second thickness change rate threshold are both determined based on the number of voltage boosts of the electrochemical device and the theoretical expansion rate of the negative electrode active material.

4. The method according to claim 3, characterized in that, The theoretical expansion rate of the negative electrode active material is determined based on the amount of silicon-carbon material mixed in the negative electrode active material, the tap density of the silicon-carbon material, and the mass percentage of silicon in the silicon-carbon material.

5. The method according to claim 1, characterized in that, The charging cutoff voltage ranges from 4.4V to 4.7V, and the discharging cutoff voltage ranges from 2.2V to 3.7V.

6. The method according to any one of claims 1 to 5, characterized in that, The method further includes: When the number of cycles of the electrochemical device is not less than 1000 or the capacity retention rate of the electrochemical device is not greater than 80%, the charge-discharge cycle of the electrochemical device shall be stopped.

7. An electrochemical device, characterized in that, include: The negative electrode active material of the electrochemical device includes a first active material and a second active material; The specific capacity of the first active material is less than that of the second active material; The discharge operating voltage range of the first active material includes a first voltage range that is not greater than the upper limit of the discharge operating voltage of the second active material; When the thickness change rate of the electrochemical device after multiple charge-discharge cycles is less than the first thickness change rate threshold, the electrochemical device is charged and discharged according to the charging cut-off voltage and the discharging cut-off voltage of the electrochemical device. When the thickness change rate of the electrochemical device after multiple charge-discharge cycles is greater than or equal to the first thickness change rate threshold and less than the second thickness change rate threshold, the discharge cut-off voltage is increased, and the electrochemical device is charged and discharged according to the charging cut-off voltage and the increased discharge cut-off voltage. When the thickness change rate of the electrochemical device after multiple charge-discharge cycles is greater than or equal to the second thickness change rate threshold, the discharge cut-off voltage is increased again, and the electrochemical device is charged and discharged according to the charge cut-off voltage and the increased discharge cut-off voltage. Wherein, the first thickness change rate threshold is less than the second thickness change rate threshold; The relationship between the thickness change rate and the current thickness of the electrochemical device and the initial thickness of the electrochemical device is expressed as follows: in, This represents the rate of change of thickness. This indicates the thickness of the current electrochemical device. This indicates the initial thickness of the electrochemical device; Increasing the discharge cutoff voltage includes: determining the amount of increase in the discharge cutoff voltage based on the amount of silicon-carbon material mixed in the negative electrode active material of the electrochemical device and the mass percentage of silicon in the silicon-carbon material; and increasing the discharge cutoff voltage according to the amount of increase in the discharge cutoff voltage.

8. The electrochemical device according to claim 7, characterized in that, The first active material includes graphite, and the second active material includes silicon-carbon material; In the negative electrode active material, the doping amount of the silicon-carbon material ranges from 1% to 99%, and the tap density of the silicon-carbon material ranges from 1.1 to 2.3 g / cm³. 3 The mass percentage of silicon in the silicon-carbon material ranges from 1% to 99%.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the electrochemical device charging and discharging method according to any one of claims 1 to 6.

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