A method for improving the cycling performance of thick electrode batteries

Abstract

The present invention provides a method for improving the cycle performance of a thick electrode battery. First, the charging boundary of the thick electrode battery is explored, and a suitable current range and a SOC value of 0%-100% are divided. By limiting the division method of the current segment and the division method of the SOC value, different SOC charging boundary values ​​corresponding to different fixed currents are found, and finally a method is formed in which a high-rate current charging can be adopted for 0-80% SOC and a low-rate current charging can be adopted for 80-100% SOC, thereby reducing the polarization phenomenon of the battery cell in a high SOC state. The charging and discharging method of the thick electrode of the present application can effectively improve the cycle performance of the thick electrode battery, and the charging method explored by the present application can achieve the effect of fast charging, effectively shorten the charging time, and the method is simple to operate, low in cost, and good in safety, and will not have adverse effects on other properties of the battery itself, thereby facilitating industrial promotion and application.

Description

Technical Field

[0001] The invention relates to the technical field of thick electrode batteries, and in particular to a method for improving the cycle performance of thick electrode batteries. Background Art

[0002] Increasing the thickness of the electrode can effectively increase the energy density of the battery cell on the one hand; on the other hand, it can reduce the proportion of inactive substances, such as conductive agents, binders, copper foil or aluminum foil, which is conducive to reducing the overall cost of the battery cell. However, increasing the thickness of the electrode will cause problems such as longer electron transmission paths and poor electrolyte wettability, which will lead to a decrease in the cycle performance of the battery cell.

[0003] In response to the above problems, researchers usually optimize and improve the cycle performance of thick electrode batteries in the following three aspects: (1) Using a new double-layer coating process, mainly by adjusting the porosity of the negative electrode to optimize the electrochemical performance, that is, using a small-particle main material close to the current collector and a large-particle main material away from the current collector, thereby optimizing the charge transfer rate during the charge and discharge process; but this process has disadvantages, that is, there will be a clear boundary between the two coatings, resulting in increased interface peeling force or interface impedance. (2) Using a new physical pore-making process, that is, using laser to form channels, but the pore-making process is cumbersome and costly, and it is difficult to be truly applied in production. (3) Using a chemical pore-making method, adding a small amount of magnetic material or pore-forming agent to the electrode slurry, the pore-forming agent volatilizes during the coating process, and bubbles are formed in the electrode to float up to produce airways, but this method is easy to introduce new substances such as magnetic materials, which are easy to pierce the diaphragm during the charge and discharge process, thereby causing safety hazards. Summary of the invention

[0004] The purpose of the present invention is to provide a method for improving the cycle performance of thick electrode batteries in view of the problems that the methods for improving the cycle performance of thick electrode batteries in the prior art have complicated processes, high costs, low safety or may cause increased battery interface peeling force. The method optimizes the charging and discharging process, reduces the polarization phenomenon of the battery under a high SOC state, and achieves the effect of improving the cycle performance of the thick electrode battery. The method is simple to operate, low in cost, and safe, and will not have an adverse effect on other properties of the battery itself, so it is easy to promote and apply in industry.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for improving the cycle performance of a thick electrode battery comprises the following steps:

[0007] Step 1: Explore the charging boundary of thick electrode batteries:

[0008] Step 11, dividing the current range of 1C to 4C into several continuous current segments, and the spacing value of each current segment is 0.5C to 1.5C; at the same time, dividing the SOC value range of 0% to 100% into several continuous SOC value segments, and the spacing value of each SOC value segment is 5% to 10%; then, in several of the continuous current segments and the 0.1C to 1C current segment, respectively select a current value to obtain several current values; in several continuous SOC value segments, respectively select a SOC value to obtain several SOC values;

[0009] Step 12, randomly select a current value from a number of current values, and use the selected current value as a fixed current to charge the thick electrode battery. The charging process is as follows: the discharged thick electrode battery is charged with a constant current from 0% SOC to a number of SOC values ​​selected in step 1 in order from small to large, and the thick electrode battery is charged to be shelved under each SOC value condition, and the voltage fluctuation curve of the thick electrode battery lithium battery during the shelving period is observed at the same time, until the curve with the first inflection point among the several voltage fluctuation curves is found, that is, the curve of the process of charging from a% SOC value to b% SOC value, then a% SOC is the SOC charging boundary value corresponding to the selected fixed current value; (wherein, a% SOC value and b% SOC value are two of the several SOC values ​​selected in step 1, and the shelved curve has a peak value and an inflection point during the process of charging from a% SOC value to b% SOC value.)

[0010] Step 13: Obtain SOC charging boundary values ​​corresponding to other current values ​​among the multiple current values ​​according to the method of step 12;

[0011] Step 2, performing cyclic charge and discharge treatment on the thick electrode;

[0012] Step 21, charging the thick electrode battery to several SOC charging boundary values ​​in sequence, using the corresponding current value as the fixed current during charging to each SOC charging boundary value, and then charging to a cut-off charging voltage with constant current and constant voltage; then, discharging to a cut-off discharge voltage with constant current;

[0013] Step 22: Perform a charge-discharge cycle test on the thick electrode battery according to the method of step 21.

[0014] The method for improving the cycle performance of thick electrode batteries provided by the present invention mainly changes the charging and discharging mode. First, the charging boundary of the thick electrode battery is explored, and the appropriate current range and the SOC value (battery state of charge) of 0%-100% are divided. By limiting the division mode of the current segment and the division mode of the SOC value, different SOC charging boundary values ​​corresponding to different fixed currents are found to ensure that under the corresponding fixed current conditions, the thick battery electrode is charged to the corresponding SOC charging boundary value and the battery will not undergo lithium deposition. Finally, a method is formed in which a high rate current (≥1C) can be used for charging at 0-80% SOC and a low rate current (0.1-1C) can be used for charging at 80-100% SOC, thereby reducing the polarization phenomenon of the battery cell under the high SOC state and effectively improving the cycle performance of the thick electrode battery. Moreover, the charging method explored by the present application can achieve the effect of fast charging and effectively shorten the charging time. Moreover, the method is simple to operate, low in cost, and safe, and will not have adverse effects on other properties of the battery itself, thereby facilitating industrial promotion and application.

[0015] Further, the thick electrode battery is a lead-acid battery, a nickel-cadmium battery, a nickel-hydrogen battery or a lithium battery. Preferably, the thick electrode battery is a lithium iron phosphate ion battery, a ternary lithium battery or a lithium iron manganese phosphate battery.

[0016] Furthermore, the thick electrode battery includes a thick electrode, the surface density of the active material layer on the current collector surface of the thick electrode is ≥200 g / ㎡, and the thickness of the thick electrode is >160 μm.

[0017] Furthermore, when the thick electrode battery is a lithium iron phosphate battery, when the temperature is ≤0°C, the charge and discharge voltage range is 2.0V~3.65V; when the temperature is >0°C, the charge and discharge voltage range is 2.5V~3.65V; when the thick electrode battery is a ternary lithium battery, a lead-acid battery or a lithium iron manganese phosphate battery, when the temperature is ≤0°C, the charge and discharge voltage range is 2.0V~4.2V; when the temperature is >0°C, the charge and discharge voltage range is 2.8V~4.2V; when the thick electrode battery is a nickel-cadmium or nickel-metal hydride battery, when the temperature is ≤0°C, the charge and discharge voltage range is 1.0V~1.4V; when the temperature is >0°C, the charge and discharge voltage range is 1.2V~1.4V.

[0018] Furthermore, in step 11, the interval value of each SOC value segment is 5% to 9%, for example, 5%, 6%, 7%, 8%, and 9%.

[0019] Furthermore, in step 11, the spacing value of each current segment is 0.8C to 1.5C, for example, 0.8C, 0.9C, 1.0C, 1.1C, 1.2C, 1.3C, 1.4C, and 1.5C.

[0020] Furthermore, in step 12, the thick electrode battery is left standing for 0.5 h to 1 h at each SOC value, which can be 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, or 1.0 h.

[0021] Furthermore, in step 12, the curve with an inflection point refers to a peak value on the smooth curve; when a peak value appears, lithium deposition occurs in the battery. The inflection point on the shelving curve indicates that during the process of lithium ions being removed from the positive electrode and embedded in the negative electrode, due to excessive charging current, a portion of the lithium ions are not completely embedded in the graphite negative electrode layered structure and are deposited on the surface of the negative electrode. During the shelving process, they are re-embedded in the negative electrode layered structure, causing the potential to shift.

[0022] Furthermore, in step 11 or step 13, the current value mC in the 0.1C to 1C current segment corresponds to the SOC charging boundary value. In step 21, during constant current and constant voltage charging to the cut-off charging voltage, the current is 0.1C to mC; during constant current discharge to the cut-off discharge voltage, the current is 0.5C to 1C. (m is a positive number)

[0023] Furthermore, step 1 and step 2 are carried out at a temperature of 20°C to 45°C.

[0024] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0025] The method for improving the cycle performance of thick electrode batteries provided by the present invention mainly changes the charging and discharging method. First, the charging boundary of the thick electrode battery is explored, and the appropriate current range and the SOC value of 0%-100% are divided. By limiting the division method of the current segment and the division method of the SOC value, different SOC charging boundary values ​​corresponding to different fixed currents are found to ensure that under the corresponding fixed current conditions, the thick battery electrode is charged to the corresponding SOC charging boundary value and lithium deposition will not occur in the battery. Finally, a high rate current (≥1C) can be used for charging at 0-80% SOC, and 80- The 100% SOC adopts a charging method with a small rate current (0.1~1C), which reduces the polarization phenomenon of the battery cell under the high SOC state. The 2000-cycle capacity retention rate can be increased by more than 14% compared with the thick electrode battery of the prior art charging and discharging method by adopting the thick electrode charging and discharging method of the present application, which effectively improves the cycle performance of the thick electrode battery. The charging method explored in the present application can achieve the effect of fast charging and effectively shorten the charging time. The method is simple to operate, low in cost, and safe. It will not have an adverse effect on other properties of the battery itself, and is convenient for industrial promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Partial shelving curve diagram under 3.5C fixed current condition in Example 1.

[0027] Figure 2 This is a diagram showing lithium deposition inside a thick electrode battery when charged to a 35% SOC value in Example 1.

[0028] Figure 3 This is a diagram showing lithium deposition inside the thick electrode when charged to 45% SOC value in Example 1. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] Example 1

[0031] Preparation of soft pack batteries

[0032] 1) Preparation of positive electrode slurry: The instrument used in the present invention is a double planetary mixer, in which lithium iron phosphate (LFP) accounts for 92% by mass, PVDF as a binder accounts for 1%, and carbon black as a conductive agent accounts for 4%. The three are mixed and evenly mixed at a certain speed in a stirring tank, and 3% by mass of NMP is added to prepare a positive electrode slurry to obtain a uniformly stirred positive electrode slurry.

[0033] 2) Preparation of positive electrode sheet: The positive electrode slurry is evenly coated on the aluminum foil, where the surface density is 300g / m 2 After drying, it is cold pressed and die-cut into strips to prepare the positive electrode sheet with a bottom thickness of 250μm.

[0034] 3) Preparation of negative electrode slurry and negative electrode sheet: 92% by mass of graphite, 2% by conductive agent carbon black, and 3% by binder PVDF are mixed evenly in a stirring tank at a certain speed, and 3% by mass of deionized water is added to prepare the negative electrode slurry. The viscosity and solid content of the negative electrode slurry are controlled, and then it is evenly coated on the copper foil and cold pressed and baked.

[0035] 4) Preparation of soft-pack battery cells: The positive electrode sheet, separator, and negative electrode sheet are assembled into a soft-pack battery in order. Subsequently, the electrolyte is injected into the battery cell under negative pressure conditions, and after sufficient rest, subsequent processes such as packaging, formation, and capacity division are carried out to obtain a thick electrode battery.

[0036] Improving the cycling performance of thick electrode batteries

[0037] Step 1: Explore the charging boundary of thick electrode batteries:

[0038] Step 11, dividing the current range of 1C to 4C into a number of continuous current segments, the spacing value of each current segment is 1C, and the number of continuous current segments are 1C to 2C, 2C to 3C, and 3C to 4C;

[0039] At the same time, the SOC value range of 0% to 100% is divided into several continuous SOC value segments, the interval value of each SOC value segment is 10%, and the several continuous SOC value segments are 0% to 10%, 10% to 20%, 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 70% to 80%, 80% to 90%, and 90% to 100%.

[0040] Then, in the several continuous current segments and the current segments of 0.1C to 1C, a current value is selected respectively, and several current values ​​are obtained, namely 0.5C, 1.5C, 2.5C and 3.5C; in the several continuous SOC value segments, a SOC value is selected respectively, and several SOC values ​​are obtained, namely 5%, 15%, 25%, 35%, 45%, 55%, 65%, 75%, 85%, 95%;

[0041] Step 12, at 25°C, select 3.5C as a fixed current, and charge the thick electrode battery. The charging process is: charge the discharged thick electrode battery from 0% SOC to 5%, 15%, 25%, 35%, 45%, 55%, 65%, 75%, 85%, and 95% at a constant current in sequence; and the thick electrode battery is left for 1 hour under each SOC value condition, with a cut-off voltage of 3.65V and a cut-off current of 0.05C. At the same time, observe the voltage fluctuation curve of the lithium battery during the shelf period until the SOC value corresponding to the curve where the inflection point first appears in several voltage fluctuation curves is found, that is, the SOC charging boundary value corresponding to the current value is obtained, such as Figure 1 As shown in the figure, under 3.5C charging conditions, a curve with an inflection point appears when charging from 35% SOC to 45% SOC. During the process of charging from 35% SOC to 45% SOC, lithium ions are removed from the positive electrode and embedded in the negative electrode. Due to the excessive charging current, a part of the lithium ions are not completely embedded in the graphite negative electrode layered structure and are precipitated on the surface of the negative electrode. During the shelving process, they are re-embedded into the negative electrode layered structure, causing the potential to shift. It can be judged that under 3.5C charging conditions, the current can be charged to 35% at a constant current without lithium precipitation, and 35% is the SOC charging boundary value corresponding to 3.5C.

[0042] At the same time, the battery charged to 35% SOC under 3.5C charging condition was disassembled, such as Figure 2 As shown in the figure, no lithium deposition occurs in the battery. The battery charged to 45% SOC under 0.35C charging condition is disassembled. Figure 3 As shown, lithium deposition occurred in the battery.

[0043] Step 13, according to the method of step 12, the SOC charging boundary value corresponding to the current value of 2.5C is 55%, the SOC charging boundary value corresponding to the current value of 1.5C is 75%, and the SOC charging boundary value corresponding to the current value of 0.5C is 85%.

[0044] Step 2, performing cyclic charge and discharge treatment on the thick electrode;

[0045] Step 21, charging the thick electrode battery to several SOC charging boundary values ​​in sequence, using the corresponding current value as the fixed current during charging to each SOC charging boundary value, and then charging to the cut-off charging voltage with constant current and constant voltage; then, discharging to the cut-off discharge voltage with constant current; specifically:

[0046] At 25°C, the thick electrode battery is charged to 35% SOC value at 3.5C current; charged to 55% SOC value at 2.5C current, charged to 75% SOC value at 1.5C current, charged to 85% SOC value at 0.5C current, and then charged to 3.65V at 0.1C current. The single charging time is 1.5h, and the 1C current is discharged to 2.5V to complete one charge and discharge. Then, the thick electrode battery is subjected to charge and discharge cycle test using step 21, and the test results are shown in Table 1.

[0047] Example 2

[0048] Preparation of soft pack batteries

[0049] 1) Preparation of positive electrode slurry: The instrument used in the present invention is a double planetary mixer, in which lithium iron phosphate (LFP) accounts for 90% by mass, PVDF as a binder accounts for 1.5%, and carbon black as a conductive agent accounts for 3.5%. The three are mixed and evenly mixed at a certain speed in a stirring tank, and 5% by mass of NMP is added to prepare a positive electrode slurry to obtain a uniformly stirred positive electrode slurry.

[0050] 2) Preparation of positive electrode sheet: The positive electrode slurry is evenly coated on the aluminum foil, where the surface density is 210g / m 2 After drying, it is cold pressed and die-cut into strips to prepare the positive electrode sheet with a bottom thickness of 180μm.

[0051] 3) Preparation of negative electrode slurry and negative electrode sheet: 90% by mass of graphite, 2% by conductive agent carbon black, and 4% by binder PVDF are mixed evenly in a stirring tank at a certain speed, and 4% by mass of deionized water is added to prepare the negative electrode slurry. The viscosity and solid content of the negative electrode slurry are controlled, and then it is evenly coated on the copper foil and cold pressed and baked.

[0052] 4) Preparation of soft-pack battery cells: The positive electrode sheet, separator, and negative electrode sheet are assembled into a soft-pack battery in order. Subsequently, the electrolyte is injected into the battery cell under negative pressure conditions, and after sufficient rest, subsequent processes such as packaging, formation, and capacity division are carried out to obtain a thick electrode battery.

[0053] Improving the cycling performance of thick electrode batteries

[0054] Step 1: Explore the charging boundary of thick electrode batteries:

[0055] Step 11, dividing the current range of 1C to 4C into a number of continuous current segments, the several continuous current segments are 1C to 1.8C, 1.8C to 2.6C, 2.6C to 3.4C, and 3.4C to 4C;

[0056] At the same time, the SOC value range of 0% to 100% is divided into several continuous SOC value segments, the interval value of each SOC value segment is 10%, and the several continuous SOC value segments are 0% to 10%, 10% to 20%, 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 70% to 80%, 80% to 90%, and 90% to 100%.

[0057] Then, in several of the continuous current segments and the current segments of 0.1C to 1C, a current value is selected respectively, and several current values ​​are obtained, which are 0.5C, 1.6C, 2.4C, 3.2C, and 4C respectively; in several of the continuous SOC value segments, a SOC value is selected respectively, and several SOC values ​​are obtained, which are 5%, 15%, 25%, 35%, 45%, 55%, 65%, 75%, 85%, and 95% respectively;

[0058] Step 12, at 30°C, 4C is selected as a fixed current, and the thick electrode battery is charged. The charging process is as follows: the discharged thick electrode battery is charged with a constant current from 0% SOC to 5%, 15%, 25%, 35%, 45%, 55%, 65%, 75%, 85%, and 95% in sequence; and the thick electrode battery is placed for 1 hour under each SOC value condition, with a cut-off voltage of 3.65V and a cut-off current of 0.05C. At the same time, the voltage fluctuation curve of the lithium battery during the placement period is observed, and the SOC values ​​corresponding to the curves with inflection points in several voltage fluctuation curves are found, that is, the SOC charging boundary value corresponding to the current value is obtained. Under the 4C charging condition, a curve with an inflection point appears for the first time when charging from 25% SOC to 35% SOC. It can be judged that under the 4C charging condition, the current can be charged to 25% with a constant current without lithium precipitation, and 25% is the SOC charging boundary value corresponding to 4C.

[0059] Step 13. According to the method of step 12, the SOC charging boundary value corresponding to the current value of 3.2C is 45%, the SOC charging boundary value corresponding to the current value of 2.4C is 65%, the SOC charging boundary value corresponding to the current value of 1.6C is 75%, and when the current value is 0.5C, there is no battery with an inflection point.

[0060] Select 0.7C as the fixed current to carry out the charging process in step 12. When the current value is 0.7C, the corresponding SOC charging boundary value is 85%.

[0061] Step 2, performing cyclic charge and discharge treatment on the thick electrode;

[0062] Step 21, charging the thick electrode battery to several SOC charging boundary values ​​in sequence, using the corresponding current value as the fixed current during charging to each SOC charging boundary value, and then charging to the cut-off charging voltage with constant current and constant voltage; then, discharging to the cut-off discharge voltage with constant current; specifically:

[0063] At 30°C, the thick electrode battery is charged to 25% SOC value at 4C current; charged to 45% SOC value at 3.2C current, charged to 65% SOC value at 2.4C current, charged to 75% SOC value at 1.6C current, charged to 85% SOC value at 0.7C current, then charged to 3.65V at 0.3C current, discharged to 2.5V at 1C current, and completed one charge and discharge. Then, the thick electrode battery is subjected to charge and discharge cycle test using step 21, and the test results are shown in Table 1.

[0064] Example 3

[0065] Preparation of soft pack batteries

[0066] 1) Preparation of positive electrode slurry: The instrument used in the present invention is a double planetary mixer, in which lithium iron phosphate (LFP) accounts for 95% by mass, PVDF as a binder accounts for 1%, and carbon black as a conductive agent accounts for 3%. The three are mixed and evenly mixed at a certain speed in a stirring tank, and 1% by mass of NMP is added to prepare a positive electrode slurry to obtain a uniformly stirred positive electrode slurry.

[0067] 2) Preparation of positive electrode sheet: The positive electrode slurry is evenly coated on the aluminum foil, where the surface density is 250g / m 2 After drying, it is cold pressed and die-cut into strips to prepare positive electrode sheets with a bottom thickness of 200μm.

[0068] 3) Preparation of negative electrode slurry and negative electrode sheet: 95% by mass of graphite, 1% by mass of conductive agent carbon black, and 3% by mass of binder PVDF are mixed evenly in a stirring tank at a certain speed, and 1% by mass of deionized water is added to prepare the negative electrode slurry. The viscosity and solid content of the negative electrode slurry are controlled, and then it is evenly coated on the copper foil and cold pressed and baked.

[0069] 4) Preparation of soft-pack battery cells: The positive electrode sheet, separator, and negative electrode sheet are assembled into a soft-pack battery in order. Subsequently, the electrolyte is injected into the battery cell under negative pressure conditions, and after sufficient rest, subsequent processes such as packaging, formation, and capacity division are carried out to obtain a thick electrode battery.

[0070] Improving the cycling performance of thick electrode batteries

[0071] Step 1: Explore the charging boundary of thick electrode batteries:

[0072] Step 11, dividing the current range of 1C to 4C into a number of continuous current segments, the spacing value of each current segment is 1.5C, and the number of continuous current segments are 1C to 2.5C and 2.5C to 4C respectively;

[0073] At the same time, the SOC value range of 0% to 100% is divided into several continuous SOC value segments, the interval value of each SOC value segment is 10%, and the several continuous SOC value segments are 0% to 10%, 10% to 20%, 20% to 30%, 30% to 40%, 40% to 50%, 50% to 60%, 60% to 70%, 70% to 80%, 80% to 90%, and 90% to 100%.

[0074] Then, in the several continuous current segments and the current segments of 0.1C to 1C, a current value is selected respectively, and several current values ​​are obtained, namely 0.6C, 2.C, and 3C; in the several continuous SOC value segments, a SOC value is selected respectively, and several SOC values ​​are obtained, namely 6%, 16%, 26%, 36%, 46%, 56%, 66%, 76%, 86%, and 96%;

[0075] Step 12, at 35°C, 3C is selected as a fixed current, and the thick electrode battery is charged. The charging process is: the discharged thick electrode battery is charged with a constant current from 0% SOC to 6%, 16%, 26%, 36%, 46%, 56%, 66%, 76%, 86%, and 96% in sequence; and the thick electrode battery is placed for 1 hour under each SOC value condition, with a cut-off voltage of 3.65V and a cut-off current of 0.05C. At the same time, the voltage fluctuation curve of the lithium battery during the placement period is observed, and the SOC values ​​corresponding to the curves with inflection points in several voltage fluctuation curves are found, that is, the SOC charging boundary value corresponding to the current value is obtained. Under the 3C charging condition, a curve with an inflection point first appears when charging from 46% SOC to 56% SOC. It can be judged that under the 3C charging condition, the current can be charged to 46% with a constant current without lithium precipitation, and 46% is the SOC charging boundary value corresponding to 3C.

[0076] Step 13: According to the method of step 12, the SOC charging boundary value corresponding to the current value of 2C is 66%, and the SOC charging boundary value corresponding to the current value of 0.6C is 86%.

[0077] Step 2, performing cyclic charge and discharge treatment on the thick electrode;

[0078] Step 21, charging the thick electrode battery to several SOC charging boundary values ​​in sequence, using the corresponding current value as the fixed current during charging to each SOC charging boundary value, and then charging to the cut-off charging voltage with constant current and constant voltage; then, discharging to the cut-off discharge voltage with constant current; specifically:

[0079] At 35°C, the thick electrode battery is charged to 46% SOC value at 3C current; charged to 66% SOC value at 2C current; charged to 86% SOC value at 0.6C current; charged to 3.65V at 0.1C current; discharged to 2.5V at 0.5C current, completing one charge and discharge. Then, the thick electrode battery is subjected to charge and discharge cycle test using step 21, and the test results are shown in Table 1.

[0080] Example 4

[0081] The thick electrode battery is a nickel-hydrogen battery purchased from Panasonic, with a thick electrode surface density of 230 g / m2 and a thickness of 215 μm.

[0082] Improving the cycling performance of thick electrode batteries

[0083] Step 1: Explore the charging boundary of thick electrode batteries:

[0084] Step 11, divide the current range of 1C to 4C into several continuous current segments, the interval value of each current segment is 0.5C, and the several continuous current segments are 1C to 1.5C, 1.5C to 2C, 2C to 2.5C, 2.5C to 3C, 3C to 3.5C, and 3.5C to 4C;

[0085] At the same time, the SOC value range of 0% to 100% is divided into several continuous SOC value segments, the interval value of each SOC value segment is 5%, and the several continuous SOC value segments are 0% to 5%, 5% to 10%, 10% to 15%, 15% to 20%, 20% to 25%, 25% to 30%, 30% to 35%, 35% to 40%, 40% to 45%, 45% to 50%, 50% to 55%, 55% to 60%, 60% to 65%, 65% to 70%, 70% to 75%, 75% to 80%, 80% to 85%, 85% to 90%, 90% to 95%, and 95% to 100%.

[0086] Then, in several of the continuous current segments and the current segments of 0.1C to 1C, a current value is selected respectively to obtain several current values, namely 0.5C, 1.5C, 2C, 2.5C, 3C, 3.5C, and 4C; in several of the continuous SOC value segments, a SOC value is selected respectively to obtain several SOC values, namely 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, and 100%;

[0087] Step 12, at 40°C, select 4C as a fixed current, and charge the thick electrode battery. The charging process is: charge the discharged thick electrode battery from 0% SOC to 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100% in sequence at a constant current; and the thick electrode battery is placed for 1 hour under each SOC value condition, with a cut-off voltage of 1.4V and a cut-off current of 0.05C. At the same time, observe the voltage fluctuation curve of the lithium battery during the placement period, find out the SOC value corresponding to the curve where the inflection point first appears in several voltage fluctuation curves, that is, obtain the SOC charging boundary value corresponding to the current value, and under the 4C charging condition, a curve with an inflection point appears when charging from 25% SOC to 35% SOC. From this, it can be judged that under 4C charging conditions, the current can be charged at a constant current to 25% without lithium deposition, and 25% is the SOC charging boundary value corresponding to 4C.

[0088] Step 13. According to the method of step 12, the SOC charging boundary value corresponding to the current value of 3.5C is 30%, the SOC charging boundary value corresponding to the current value of 3C is 45%, the SOC charging boundary value corresponding to the current value of 2.5C is 55%, the SOC charging boundary value corresponding to the current value of 2C is 60%, the SOC charging boundary value corresponding to the current value of 1.5C is 75%, and the SOC charging boundary value corresponding to the current value of 0.5C is 90%.

[0089] Step 2, performing cyclic charge and discharge treatment on the thick electrode;

[0090] Step 21, charging the thick electrode battery to several SOC charging boundary values ​​in sequence, using the corresponding current value as the fixed current during charging to each SOC charging boundary value, and then charging to the cut-off charging voltage with constant current and constant voltage; then, discharging to the cut-off discharge voltage with constant current; specifically:

[0091] At 40°C, the thick electrode battery is charged to 25% SOC value at 4C current; charged to 30% SOC value at 3.5C current, charged to 45% SOC value at 3C current, charged to 55% SOC value at 2.5C current, charged to 60% SOC value at 2C current, charged to 75% SOC value at 1.5C current, charged to 90% SOC value at 0.5C current, then charged to 1.4V at 0.1C current, discharged to 1.2V at 1C current, and completed one charge and discharge. Then, the thick electrode battery is subjected to charge and discharge cycle test using step 21, and the test results are shown in Table 1.

[0092] Example 5

[0093] The thick electrode battery is a lead-acid battery purchased from Panasonic, and the surface density of the thick electrode is 285g / m 2 , the thickness of the bottom is 225μm.

[0094] Improving the cycling performance of thick electrode batteries

[0095] Step 1: Explore the charging boundary of thick electrode batteries:

[0096] Step 11, dividing the current range of 1C to 4C into a number of continuous current segments, the spacing value of each current segment is 1C, and the number of continuous current segments are 1C to 2C, 2C to 3C, and 3C to 4C;

[0097] At the same time, the SOC value range of 0% to 100% is divided into several continuous SOC value segments, the interval value of each SOC value segment is 8%, and the several continuous SOC value segments are 0% to 8%, 8% to 16%, 16% to 24%, 24% to 32%, 32% to 40%, 40% to 48%, 48% to 56%, 56% to 64%, 64% to 72%, 72% to 80%, 80% to 88%, 88% to 96%, and 96% to 100%.

[0098] Then, in several of the continuous current segments and the current segments of 0.1C to 1C, a current value is selected respectively, and several current values ​​are obtained, which are 0.5C, 1.5C, 2.5C and 3.5C respectively; in several of the continuous SOC value segments, a SOC value is selected respectively, and several SOC values ​​are obtained, which are 8%, 16%, 24%, 32%, 40%, 48%, 56%, 64%, 72%, 80%, 88%, 96% respectively;

[0099] Step 12, at 45°C, select 3.5C as a fixed current, and charge the thick electrode battery. The charging process is: the discharged thick electrode battery is charged with a constant current from 0% SOC to 8%, 16%, 24%, 32%, 40%, 48%, 56%, 64%, 72%, 80%, 88%, and 96% in sequence; and the thick electrode battery is placed for 1 hour under each SOC value condition, with a cut-off voltage of 4.2V and a cut-off current of 0.05C. At the same time, the voltage fluctuation curve of the lithium battery during the placement period is observed, and the SOC value corresponding to the curve with an inflection point in several voltage fluctuation curves is found, that is, the SOC charging boundary value corresponding to the current value is obtained. Under the 3.5C charging condition, a curve with an inflection point appears when charging from 40% SOC to 48% SOC. It can be judged that under the 3.5C charging condition, the current can be charged to 40% with a constant current without lithium precipitation, and 40% is the SOC charging boundary value corresponding to 3.5C.

[0100] Step 13. According to the method of step 12, the SOC charging boundary value corresponding to the current value of 2.5C is 56%, the SOC charging boundary value corresponding to the current value of 1.5C is 72%, and the SOC charging boundary value corresponding to the current value of 0.5C is 88%.

[0101] Step 2, performing cyclic charge and discharge treatment on the thick electrode;

[0102] Step 21, charging the thick electrode battery to several SOC charging boundary values ​​in sequence, using the corresponding current value as the fixed current during charging to each SOC charging boundary value, and then charging to the cut-off charging voltage with constant current and constant voltage; then, discharging to the cut-off discharge voltage with constant current; specifically:

[0103] At 45°C, the thick electrode battery is charged to 40% SOC value at 3.5C current; charged to 56% SOC value at 2.5C current; charged to 72% SOC value at 1.5C current; charged to 88% SOC value at 0.5C current; then charged to 4.2V at 0.1C current; discharged to 2.8V at 1C current, completing one charge and discharge. Then, the thick electrode battery is subjected to charge and discharge cycle test using step 21, and the test results are shown in Table 1.

[0104] Comparative Example 1

[0105] The thick electrode batteries of Examples 1-5 were respectively subjected to cycle performance tests in the conventional charge and discharge manner of the prior art. During the charge and discharge process of Comparative Example 1, the temperature conditions were the same as those of Examples 1-5.

[0106] Among them, in Comparative Example 1, the thick electrode battery prepared in Example 1 is charged and discharged in the following manner: 0.33C constant current charging to 3.65V, cut-off current 0.05C, charging time 2.5h, 0.33C constant current discharging to 2.5V, and cyclic charging and discharging.

[0107] The thick electrode battery prepared in Example 2 is charged and discharged in the following manner: 0.5C constant current charging to 3.65V, cut-off current 0.05C, 0.5C constant current discharging to 2.5V, and cyclic charging and discharging.

[0108] The thick electrode prepared in Example 3 is charged and discharged in the following manner: 3C constant current charging to 3.65V, cut-off current 0.05C, 0.5C constant current discharging to 2.5V, and cyclic charging and discharging.

[0109] The thick electrode prepared in Example 4 is charged and discharged in the following manner: 2C constant current charging to 1.4V, cut-off current 0.05C, 0.5C constant current discharging to 1.2V, and cyclic charging and discharging.

[0110] The thick electrode prepared in Example 5 is charged and discharged in the following manner: 1.5C constant current charging to 4.2V, cut-off current 0.05C, 0.5C constant current discharging to 2.8V, and cyclic charging and discharging.

[0111] The test results are shown in Table 1. The thick electrode batteries of Example 1 are marked as Comparative Example 1-1 group, the thick electrode batteries of Example 2 are marked as Comparative Example 1-2 group, the thick electrode batteries of Example 3 are marked as Comparative Example 1-3 group, the thick electrode batteries of Example 4 are marked as Comparative Example 1-4 group, and the thick electrode batteries of Example 5 are marked as Comparative Example 1-5 group.

[0112] Comparative Example 2

[0113] Comparative Example 2 uses the same soft-pack battery as Example 1, but does not select the current in the 0.1-1C current range. The specific charging and discharging method is:

[0114] At 25°C, the thick electrode battery is charged to 35% SOC value at 3.5C current; charged to 55% SOC value at 2.5C current; charged to 75% SOC value at 1.5C current; charged to 3.65V at 1.2C current; discharged to 2.5V at 1C current, completing one charge and discharge. Then, the thick electrode battery is subjected to charge and discharge cycle test using step 21, and the test results are shown in Table 1.

[0115] Comparative Example 3

[0116] Comparative Example 3 uses the soft-pack battery prepared in Example 1, and Comparative Example 3 changes the charging method of Example 1, as shown below:

[0117] At 25°C, the thick electrode battery is charged to 35% SOC value at 2.5C current; charged to 55% SOC value at 1.5C current; charged to 75% SOC value at 0.5C current; charged to 85% SOC value at 1C current; then charged to 3.65V at 0.1C current; discharged to 2.5V at 1C current, completing one charge and discharge. Then, the thick electrode battery is subjected to charge and discharge cycle test using step 21, and the test results are shown in Table 1.

[0118] Table 1

[0119]

[0120] As shown in Table 1, the thick electrode charge and discharge method of the present application can effectively improve the cycle performance of thick electrode batteries, and the 2000-cycle capacity retention rate can be increased by more than 14% compared with the thick electrode batteries of the prior art charge and discharge method.

[0121] By limiting the division method of current segments and the division method of SOC values, different SOC charging boundary values ​​corresponding to different fixed currents are found to ensure that under the corresponding fixed current conditions, the thick battery electrode is charged to the corresponding SOC charging boundary value without lithium deposition. Finally, a method is formed in which a high rate current (≥1C) can be used for charging at 0-80% SOC and a low rate current (0.1-1C) can be used for charging at 80-100% SOC. The polarization phenomenon of the battery cell under high SOC state is reduced, and the cycle performance of the thick electrode battery is effectively improved. The charging method explored in the present application can achieve the effect of fast charging and effectively shorten the charging time. The method is simple to operate, low in cost, and safe. It will not have an adverse effect on other properties of the battery itself, and is convenient for industrial promotion and application.

[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the cycle performance of thick electrode batteries, characterized in that: The following steps are involved: Step 1: Explore the charging boundary of thick electrode batteries: Step 11, dividing the current range of 1C to 4C into several continuous current segments, and the spacing value of each current segment is 0.5C to 1.5C; at the same time, dividing the SOC value range of 0% to 100% into several continuous SOC value segments, and the spacing value of each SOC value segment is 5% to 10%; then, in several of the continuous current segments and the 0.1C to 1C current segment, respectively select a current value to obtain several current values; in several continuous SOC value segments, respectively select a SOC value to obtain several SOC values; Step 12, randomly select a current value from a number of current values, use the selected current value as a fixed current, and charge the thick electrode battery. The charging process is as follows: the discharged thick electrode battery is charged with a constant current from 0% SOC to a number of SOC values ​​selected in step 1 in order from small to large, and the thick electrode battery is placed under the condition of each SOC value, and the voltage fluctuation curve of the thick electrode battery during the placement period is observed, until the curve with the first inflection point among the several voltage fluctuation curves is found, that is, the curve of the process of charging from a% SOC value to b% SOC value, then a% SOC is the SOC charging boundary value corresponding to the selected fixed current value; Step 13: Obtain SOC charging boundary values ​​corresponding to other current values ​​among the multiple current values ​​according to the method of step 12; Step 2, performing cyclic charge and discharge treatment on the thick electrode; Step 21, charging the thick electrode battery to several SOC charging boundary values ​​in sequence, using the corresponding current value as the fixed current during charging to each SOC charging boundary value, and then charging to the cut-off charging voltage with constant current and constant voltage; and discharging to the cut-off discharge voltage with constant current; Step 22, performing charge and discharge cycle treatment on the thick electrode battery according to the method of step 21; Wherein, in step 12 or step 13, when the current value selected in the 0.1C to 1C current segment is used as the fixed current, if a curve with an inflection point does not appear, a larger current value is selected in the 0.1C to 1C current segment as the fixed current until the corresponding SOC charging boundary value in the 0.1C to 1C current segment is obtained; In step 11 or step 13, the current value m C in the current segment of 0.1C to 1C corresponds to the SOC charging boundary value. In step 21, during constant current and constant voltage charging to the cut-off charging voltage, the current is 0.1C to m C; during constant current discharge to the cut-off discharge voltage, the current is 0.5C to 1C.

2. The method for improving the cycle performance of thick electrode batteries according to claim 1, characterized in that: Thick electrode batteries are lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries or lithium batteries.

3. The method for improving the cycle performance of thick electrode batteries according to claim 2, characterized in that: The thick electrode battery comprises a thick electrode, the surface density of the active material layer on the current collector surface of the thick electrode is ≥200g / ㎡, and the thickness of the thick electrode is >160μm.

4. The method for improving the cycle performance of thick electrode batteries according to claim 1, characterized in that: In step 11, the interval value of each SOC value segment is 5% to 9%.

5. The method for improving the cycle performance of thick electrode batteries according to claim 4, characterized in that: In step 11, the spacing value of each current segment is 0.8C to 1.5C.

6. The method for improving the cycle performance of thick electrode batteries according to claim 5, characterized in that: In step 12, the shelf treatment time is 0.5h to 1h.

7. The method for improving the cycle performance of thick electrode batteries according to claim 6, characterized in that: In step 12, the curve with an inflection point refers to a smooth curve with a peak value; when the peak value appears, lithium deposition occurs in the battery.

8. The method for improving the cycle performance of thick electrode batteries according to any one of claims 1 to 7, characterized in that: The step 1 and the step 2 are carried out at a temperature of 20°C to 45°C.

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