Lithium ion battery NP ratio optimization method, evaluation method and lithium ion battery

Abstract

The invention discloses a lithium ion battery NP ratio optimization method and evaluation method and a lithium ion battery, and the method comprises the steps: determining the grading standard of positive and negative pole pieces according to the design information of the battery; sampling the coated, rolled and cut positive and negative pole pieces by adopting a'nine-point sampling method-three-time sampling 'by using a sampler; numbering and weighing the sampled positive and negative pole pieces, recording the weight of the corresponding pole pieces, calculating the average value of the weight of the sampled pole pieces, and marking the gears of the positive and negative pole pieces according to a grading standard; carrying out matched winding on the positive and negative pole pieces according to the pole piece gears and the set gear matching standard and the pole piece matching principle; evaluating the NP ratio range of the positive electrode and the negative electrode of the battery and producing the battery based on the optimization method of the NP ratio of the lithium ion battery; the problem that the NP ratio deviation is large is effectively solved, the actual NP ratio range of the battery is more concentrated and is close to the ideal NP ratio, and the NP ratio accuracy, the product production stability and the product performance of the lithium ion battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of storage batteries, and more particularly to an optimization method and an evaluation method for the NP ratio of a lithium-ion battery and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries, as a recyclable and convenient mobile power source, are widely sought after by the public, and their excellent properties such as being green and environmentally friendly, high energy density, safe and reliable, and low price also play a decisive role in their rapid development.

[0003] However, in terms of the production process of lithium-ion batteries, the NP ratio will directly affect the various performance indicators of the battery. When the NP ratio is too high, the battery design cost increases, the negative electrode sheet is thicker, and the battery thickness is too thick; it will also cause the lithium ions released from the positive electrode to be over-embedded in the negative electrode, and the number of recoverable lithium ions will be reduced, resulting in low initial efficiency of lithium-ion batteries and decreased battery cycle retention rate; when the NP ratio is too low, the lithium ions cannot be fully embedded in the negative electrode material, which will cause the battery capacity, rate and cycle performance to deteriorate at the same time; in severe cases, the lithium-ion battery may cause abnormal lithium deposition, which will cause the battery safety performance to decline, catch fire, explode, etc. Therefore, in the production process of lithium-ion batteries, improving the utilization rate of the positive and negative NP ratios of lithium-ion batteries is crucial to reducing battery design costs and improving various chemical properties and safety performance of batteries.

[0004] At present, the main method for controlling the NP ratio of battery production in the industry is: during process design, the theoretical positive and negative electrode surface density is calculated according to the designed NP ratio, and then the coating surface density accuracy is controlled to make it as close as possible to the process surface density, thereby achieving the purpose of controlling the NP ratio of the produced battery.

[0005] However, on the one hand, this method ignores the fact that the actual NP of the electrode is relatively large or small due to rolling and stretching problems in the subsequent production process, which in turn has an adverse effect on battery performance; on the other hand, this control method has high requirements on the accuracy and stability of the electrode coating surface density, and there is a greater risk of production anomalies, which is prone to batch production defects.

[0006] Therefore, how to reduce the actual NP ratio caused by production process factors to be larger or smaller, so as to quickly and accurately achieve the optimal utilization of the NP ratio in the production battery, thereby improving the performance of the battery is an urgent problem that technicians in this field need to solve. Summary of the invention

[0007] In view of this, the present invention provides a method for optimizing the NP ratio of a lithium-ion battery, an evaluation method, and a lithium-ion battery to solve some of the technical problems mentioned in the background technology.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] A method for optimizing the NP ratio of a lithium-ion battery comprises the following steps:

[0010] S1. Determine the classification standards of positive and negative electrodes based on battery design information;

[0011] S2. Use a sampler of a certain area and adopt the "nine-point sampling method - three samplings" to sample the positive and negative electrode sheets after coating, rolling and slitting according to the process requirements;

[0012] S3. Number, weigh and record the corresponding electrode weights of the sampled positive and negative electrodes, calculate the average weight of the sampled electrodes, and mark the positive and negative electrode positions according to the positive and negative electrode classification standards;

[0013] S4. Match and wind the positive and negative electrode sheets according to the set matching standards and matching principles based on the positive and negative electrode sheet positions.

[0014] Preferably, in step S1, the method for calculating and obtaining the positive and negative electrode classification standards is:

[0015] Upper and lower limits of grade weight = (Z B *S+(Z+nQ)*S)*X*3

[0016] Among them, Z B is the surface density of the foil, S is the sampling area of ​​the sampler, Z is the limit surface density in the process, n is the error coefficient of the bin interval, Q is the error value of the bin interval, and X is the roller pressure correction coefficient;

[0017] Roll pressure correction factor X is:

[0018] X=1-Y

[0019] Wherein, Y is the pole piece rolling extension rate, Y = (pole piece length after rolling - pole piece length before rolling) / pole piece length before rolling * 100%;

[0020] The bin interval error coefficient n is the integer quotient of the coating machine accuracy and the bin interval error value;

[0021] The grading order is carried out in descending order of surface density. Specifically: the maximum positive error value of coating accuracy is the upper limit value of the first gear in the grading standard, and the maximum negative error value of coating accuracy is the lower limit value of the last gear in the grading standard.

[0022] Preferably, the specific content of step S2 is:

[0023] The positive electrode sheets and the negative electrode sheets are coated, rolled and cut according to the process requirements;

[0024] Take the positive and negative pole pieces from each small roll at the head, middle and tail positions respectively;

[0025] After taking the slices, the taken electrode slices are divided into nine equal parts according to the area, and each of the nine equal parts is sampled according to the geometric center position.

[0026] Preferably, the matching standard is that the positive electrode sheet matched with the negative electrode sheet is not higher than the negative electrode sheet, and the matching principle is that the same grade is given priority, and the nearest grade is matched if the grade is downgraded.

[0027] Preferably, the maximum gear difference between the negative electrode plate and the matching positive electrode plate is 2 gears.

[0028] Preferably, the NP ratio of the pole pieces of the different gears is greater than the NP ratio of the pole pieces of the same gear.

[0029] A method for evaluating the NP ratio of a lithium-ion battery, based on the optimization method for the NP ratio of a lithium-ion battery, when the negative electrode sheet and the positive electrode sheet are matched for use, the NP ratio range of the positive and negative electrodes of the lithium-ion battery is:

[0030] The minimum NP ratio when the same-level pole pieces are matched is: the NP ratio when the lower limit of the negative pole piece of the same level is matched with the upper limit of the positive pole piece of the same level;

[0031] The maximum NP ratio when the differential pole pieces are matched is: the NP ratio when the upper limit pole piece of the high-gear negative pole piece is matched with the lower limit pole piece of the low-gear positive pole piece.

[0032] Preferably, the minimum NP ratio when the pole pieces of the same gear are matched is specifically:

[0033] When the negative electrode surface density - the positive electrode surface density < Q, the minimum NP ratio of the same-level pole pieces decreases as the level decreases. At this time, the minimum NP is the NP ratio of the lowest-level positive and negative pole pieces.

[0034] When the negative electrode surface density - the positive electrode surface density > Q, the minimum NP ratio when the same-level pole pieces are matched increases as the gear decreases. At this time, the minimum NP is the NP ratio when the positive and negative pole pieces are matched at the highest level.

[0035] Preferably, the maximum NP ratio when the differential pole piece is matched is specifically:

[0036] When the positive electrode surface density - the negative electrode surface density > 2Q, the maximum NP ratio of the differential electrode piece matching decreases as the gear position decreases. At this time, the maximum NP is the NP ratio when the upper limit electrode piece of the highest gear negative electrode piece is matched with the lower limit electrode piece of the low gear positive electrode piece;

[0037] When the positive electrode surface density - the negative electrode surface density is less than 2Q, the maximum NP ratio of the differential electrode piece increases as the gear position decreases. At this time, the maximum NP is the NP ratio of the upper limit electrode piece of the lowest gear negative electrode piece and the lower limit electrode piece of the low gear positive electrode piece.

[0038] A lithium-ion battery is manufactured by using the lithium-ion battery NP ratio optimization method.

[0039] Through the above technical solutions, it can be known that compared with the prior art, the present invention discloses a method for optimizing the NP ratio of a lithium-ion battery, an evaluation method and a lithium-ion battery. By using the "nine-point sampling method-three-time sampling" for sampling and weighing, and calculating the average value as the sampling weight for gear matching, the comprehensiveness of sampling can be effectively improved, and the weight distortion problem caused by the abnormality of individual sampling points can be avoided, thereby ensuring the accuracy of the pole piece gearing; by using the same punch sampler for sampling and weighing, the weight distortion problem caused by the coating size error can be avoided, and the pole piece gearing can be ensured to be more accurate; by determining the increasing and decreasing relationship between the estimated positive and negative electrode surface density settings and the maximum NP ratio and the minimum NP ratio, the NP ratio range of the battery made by the method of the present invention can be quickly determined, which is conducive to realizing the application control of the NP ratio; by using the method of the present invention to match the positive and negative pole pieces, the large NP ratio deviation caused by equipment accuracy errors and production process abnormalities can be effectively reduced, so that the actual NP ratio range of the battery made by the present invention is more concentrated and close to the ideal NP ratio, which has guiding significance for improving the accuracy of the NP ratio of lithium-ion batteries, product production stability and product performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0041] Figure 1 A schematic diagram of a method for optimizing the NP ratio of a lithium-ion battery provided by the present invention;

[0042] Figure 2 A schematic diagram of the electrode sampling method using the "nine-point sampling method - three-time sampling" provided by the present invention;

[0043] Figure 3 A schematic diagram of the sampling data of the positive electrode sheet provided by the present invention;

[0044] Figure 4 A schematic diagram of the negative electrode plate sampling data provided by the present invention;

[0045] Figure 5 A schematic diagram of high temperature short circuit test results of batteries prepared in the embodiments and comparative examples provided by the present invention;

[0046] Figure 6A bar chart comparing the first effects of batteries prepared in the embodiments and comparative examples provided by the present invention;

[0047] Figure 7 A cycle comparison curve diagram of batteries prepared in the embodiments and comparative examples provided by the present invention;

[0048] Figure 8 The figure is a rate comparison curve of the batteries prepared in the embodiments and comparative examples provided by the present invention. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] Embodiment 1 discloses a method for optimizing the NP ratio of a lithium-ion battery, such as Figure 1 As shown, the following steps are included:

[0051] S1. Determine the classification standards of positive and negative electrodes based on battery design information;

[0052] S2. Use a sampler of a certain area and adopt the "nine-point sampling method - three samplings" to sample the positive and negative electrodes after coating, rolling and slitting according to the process requirements;

[0053] S3. Number, weigh and record the corresponding electrode weights of the sampled positive and negative electrodes, calculate the average weight of the sampled electrodes, and mark the positive and negative electrode positions according to the positive and negative electrode classification standards;

[0054] S4. Match and wind the positive and negative electrode sheets according to the set matching standards and matching principles based on the positive and negative electrode sheet positions.

[0055] In this embodiment, a 1160100-10000mAh lithium-ion battery is taken as an example to provide a specific example, which is only a part of the embodiments of the present invention, but not all of the embodiments.

[0056] In this embodiment, the positive electrode current collector is made of 12um aluminum foil (the foil surface density is 34g / m 2 ), the negative electrode current collector uses 6um copper foil (the foil surface density is 53g / m 2 ), the positive electrode surface density standard is 378g / m 2 The negative electrode surface density standard is 218g / m 2The gram capacity of the positive electrode active material is 171.6mAh / g, the gram capacity of the negative electrode active material is 340mAh / g, the positive electrode active material accounts for 96.6%, the negative electrode active material accounts for 95.0%, the positive electrode design pole piece length is 1752mm, the negative electrode design pole piece length is 1711mm, the measured positive pole piece length after rolling is 1760mm, the measured negative pole piece length after rolling is 1716mm, the coating machine accuracy is ±4g / m 2 , the coating interval error value of the grading process is 2g / m 2 , the sampling area of ​​the sampler is 800mm2.

[0057] In order to further implement the above technical solution, in step S1, the calculation method for obtaining the positive and negative electrode sheet classification standard is:

[0058] Upper and lower limits of grade weight = (Z B *S+(Z+nQ)*S)*X*3

[0059] Among them, Z B is the surface density of the foil, S is the sampling area of ​​the sampler, Z is the limit surface density in the process, n is the error coefficient of the bin interval, Q is the error value of the bin interval, and X is the roller pressure correction coefficient;

[0060] Roll pressure correction factor X is:

[0061] X=1-Y

[0062] Wherein, Y is the pole piece rolling extension rate, Y = (pole piece length after rolling - pole piece length before rolling) / pole piece length before rolling * 100%;

[0063] In this example, the pole piece rolling extension rate Y is:

[0064] Y 正极 =(1760-1752) / 1752*100%=0.46%

[0065] Y 负极 =(1716-1711) / 1711*100%=0.29%

[0066] The pole piece rolling correction factor X is:

[0067] X 正极 =1-Y 正极 =1-0.46%=99.54%

[0068] X 负极 =1-Y 负极 =1-0.29%=99.71%;

[0069] The bin interval error coefficient n is the integer quotient of the coating machine accuracy and the bin interval error value;

[0070] In this example, the bin interval error coefficient n is specifically calculated as:

[0071] Coating machine accuracy is ±4g / m 2 , the coating interval error value of the grading process is 2g / m 2 , then we can know that the error coefficient n can be -2, -1, 0, 1, 2;

[0072] The grading order is carried out in descending order of surface density. Specifically, the maximum positive error value of coating accuracy is the upper limit value of the first grading position in the grading standard, and the maximum negative error value of coating accuracy is the lower limit value of the last grading position in the grading standard.

[0073] In this example, the calculation of the positive electrode grading standard is as follows:

[0074] Lower limit of level 1 = (34*800 / 1000000 + (378+1*2)*800 / 1000000)*99.54%*3 = 0.989g

[0075] The upper limit of level 1 = (34*800 / 1000000 + (378+2*2)*800 / 1000000)*99.54%*3 = 0.994g, so the weight standard of the pole piece of level 1 is: 0.989g~0.994g;

[0076] 2nd gear lower limit = (34*800 / 1000000 + (378+0*2)*800 / 1000000)*99.54%*3 = 0.984g 2nd gear upper limit = (34*800 / 1000000 + (378+1*2)*800 / 1000000)*99.54%*3 = 0.989g Then the 2nd gear pole piece weight standard is: 0.984g ~ 0.989g;

[0077] 3rd gear lower limit = (34*800 / 1000000 + (378-1*2)*800 / 1000000)*99.54%*3 = 0.979g3rd gear upper limit = (34*800 / 1000000 + (378+0*2)*800 / 1000000)*99.54%*3 = 0.984g Then the 3rd gear pole piece weight standard is: 0.979g ~ 0.984g;

[0078] 4th gear lower limit = (34*800 / 1000000 + (378-2*2)*800 / 1000000)*99.54%*3 = 0.975g 4th gear upper limit = (34*800 / 1000000 + (378-1*2)*800 / 1000000)*99.54%*3 = 0.979g Then the 1st gear pole piece weight standard is: 0.975g ~ 0.979g;

[0079] That is, the classification standards for positive electrode sheets are as follows:

[0080] Level 1: 0.989g to 0.994g;

[0081] 2nd gear: 0.984g~0.989g;

[0082] 3rd gear: 0.979g~0.984g;

[0083] 4th gear: 0.975g~0.979g;

[0084] The calculation of the negative electrode plate classification standard is as follows: 1st grade lower limit = (53*800 / 1000000 + (218 + 1*2) * 800 / 1000000) * 99.71% * 3 = 0.653g 1st grade upper limit = (53*800 / 1000000 + (218 + 2*2) * 800 / 1000000) * 99.71% * 3 = 0.658g Then the 1st grade electrode weight standard is: 0.653g ~ 0.658g;

[0085] 2nd gear lower limit = (53*800 / 1000000+(218+0*2)*800 / 1000000)*99.71%*3=0.648g 2nd gear upper limit = (53*800 / 1000000+(218+1*2)*800 / 1000000)*99.71%*3=0.653g Then the 2nd gear pole piece weight standard is: 0.648g~0.653g;

[0086] Lower limit of level 3 = (53*800 / 1000000+(218-1*2)*800 / 1000000)*99.71%*3=0.643g

[0087] The upper limit of level 3 = (53*800 / 1000000+(218+0*2)*800 / 1000000)*99.71%*3=0.648g, so the weight standard of level 3 pole piece is: 0.643g~0.648g;

[0088] 4th gear lower limit = (53*800 / 1000000+(218-2*2)*800 / 1000000)*99.71%*3=0.639g

[0089] The upper limit of level 4 = (53*800 / 1000000+(218-1*2)*800 / 1000000)*99.71%*3=0.643g, so the weight standard of level 4 pole piece is: 0.639g~0.643g;

[0090] That is, the negative electrode is divided into the following categories:

[0091] 1st gear: 0.653g~0.658g;

[0092] 2nd gear: 0.648g~0.653g;

[0093] Level 3: 0.643g~0.648g;

[0094] 4th gear: 0.639g~0.643g;

[0095] In order to further implement the above technical solution, the specific content of step S2 is:

[0096] The positive electrode sheets and the negative electrode sheets are coated, rolled and cut according to the process requirements;

[0097] Take the positive and negative pole pieces from each small roll at the head, middle and tail positions respectively;

[0098] After taking the slices, divide the taken electrode into nine equal parts according to the area, and sample each electrode according to the geometric center position after the nine equal parts, such as Figure 2 shown.

[0099] In this embodiment, the sampling area must be kept consistent and the same punch sampler is used for sampling. For example, the area used is 800mm 2 The punch sampler is used for sampling;

[0100] Number, weigh and record the corresponding weight (M 1+ 、M 2+ 、M 3+ 、M 4+ ...M 9+ ), calculate the average value M j+ =(M 1+ +M 2+ +M 3+ +M 4+ +M 5+ +M 6+ +M 7+ +M 8+ +M 9+ ) / 9, and mark the pole piece position, the specific data is as follows Figure 3 As shown; the negative electrode pieces after sampling are numbered, weighed, and the corresponding weights are recorded (M 1- 、M 2- 、M 3- 、M 4- ...M 9- ), calculate the average value M j- =(M 1- +M 2- +M 3- +M 4- +M 5- +M6- +M 7- +M 8- +M 9- ) / 9, and mark the pole piece position, the specific data is as follows Figure 4 As shown;

[0101] In practical applications, it is necessary to ensure that the weighing equipment (such as an electronic scale) used to weigh the positive and negative electrode sampling pieces has an accuracy of one thousandth and is the same equipment that is recalibrated before use to reduce the impact of weighing errors on experimental results.

[0102] In order to further implement the above technical solution, the matching standard is that the positive electrode sheet matched with the negative electrode sheet should not be higher than the negative electrode sheet, and the matching principle is that the same grade is given priority, and downgraded grades are matched with the nearest grade.

[0103] In order to further implement the above technical solution, the maximum gear difference between the negative electrode plate and the matching positive electrode plate is 2 gears.

[0104] In order to further implement the above technical solution, the NP ratio of the pole pieces of different gears is greater than the NP ratio of the pole pieces of the same gear.

[0105] In this example, according to the set matching standards and matching principles for the positive and negative electrode sheet positions, it can be determined that the negative electrode 1-2 coil and the positive electrode 1-1 coil are used for electrode sheet matching winding.

[0106] Embodiment 2

[0107] A method for evaluating the NP ratio of a lithium-ion battery, based on an optimization method for the NP ratio of a lithium-ion battery, is used to match the negative electrode sheet with the positive electrode sheet. The range of the NP ratio of the positive and negative electrodes of the lithium-ion battery is:

[0108] The minimum NP ratio when the same-level pole pieces are matched is: the NP ratio when the lower limit of the negative pole piece of the same level is matched with the upper limit of the positive pole piece of the same level;

[0109] The maximum NP ratio when the differential pole pieces are matched is: the NP ratio when the upper limit pole piece of the high-gear negative pole piece is matched with the lower limit pole piece of the low-gear positive pole piece.

[0110] In order to further implement the above technical solution, the minimum NP ratio when the same gear pole piece is matched is specifically:

[0111] When the negative electrode surface density - the positive electrode surface density < Q, the minimum NP ratio of the same-level pole pieces decreases as the level decreases. At this time, the minimum NP is the NP ratio of the lowest-level positive and negative pole pieces.

[0112] When the negative electrode surface density - the positive electrode surface density > Q, the minimum NP ratio when the same-level pole pieces are matched increases as the gear decreases. At this time, the minimum NP is the NP ratio when the positive and negative pole pieces are matched at the highest level.

[0113] In order to further implement the above technical solution, the maximum NP ratio when the differential pole piece is matched is specifically:

[0114] When the positive electrode surface density - the negative electrode surface density > 2Q, the maximum NP ratio of the differential electrode piece matching decreases as the gear position decreases. At this time, the maximum NP is the NP ratio when the upper limit electrode piece of the highest gear negative electrode piece is matched with the lower limit electrode piece of the low gear positive electrode piece;

[0115] When the positive electrode surface density - the negative electrode surface density is less than 2Q, the maximum NP ratio of the differential electrode piece increases as the gear position decreases. At this time, the maximum NP is the NP ratio of the upper limit electrode piece of the lowest gear negative electrode piece and the lower limit electrode piece of the low gear positive electrode piece.

[0116] In this embodiment, NP ratio = negative electrode actual surface density * negative electrode active material gram capacity * negative electrode active material ratio * negative electrode rolling correction coefficient / (positive electrode actual surface density * positive electrode active material gram capacity * positive electrode active material ratio * positive electrode rolling correction coefficient).

[0117] In this embodiment, the NP ratio of the positive and negative electrodes of the battery ranges from 1.111 to 1.146, and the specific calculation process is as follows:

[0118] Negative electrode surface density = - positive electrode surface density = 218 g / m 2 -378g / m 2 <2g / m 2 At this time, when the same-level pole piece is matched, the minimum NP ratio decreases as the level decreases. It can be seen that the minimum NP ratio is the NP ratio when the negative 4-level lower limit pole piece is matched with the positive 4-level upper limit pole piece, that is:

[0119] NP min =(218-4)*340*95%*99.71% / ((378-2)*171.6*96.6%*99.54%)=1.111

[0120] Positive electrode surface density - negative electrode surface density = 378g / m 2 -218g / m 2 >2*2g / m 2 At this time, the maximum NP ratio of the differential gear pole piece matching decreases as the gear position decreases. It can be seen that the maximum NP ratio is the NP ratio when the upper limit pole piece of the negative electrode 1 gear is matched with the lower limit pole piece of the positive electrode 2 gear, that is:

[0121] NP max =(218+4)*340*95%*99.71% / (378*171.6*96.6%*99.54%)=1.146

[0122] Through the above calculations, it can be known that when a lithium-ion battery NP ratio optimization method is used to match the negative electrode sheet and the positive electrode sheet, the actual NP ratio range of the battery is: 1.111-1.146.

[0123] Embodiment 3

[0124] A lithium-ion battery is manufactured by using a lithium-ion battery NP ratio optimization method.

[0125] In this embodiment, taking the 1160100-10000mAh lithium-ion battery electrode in the first embodiment as an example, two comparative examples are used to compare the performance of lithium-ion batteries made by the present invention using a lithium-ion battery NP ratio optimization method.

[0126] Comparative Example 1

[0127] When winding, the positive electrode uses a positive electrode sheet whose density after coating is the upper limit of the coating accuracy, that is, the positive electrode surface density is 378+4=382g / m 2 The negative electrode uses a negative electrode with a density of 218-4 = 214g / m 2 The electrode is produced, and the resulting battery is the minimum NP ratio battery under the conventional production method. After production is completed, the battery performance is tested.

[0128] Comparative Example 2

[0129] The 1160100-10000mAh lithium-ion battery pole piece in Example 1 is used. When winding, the positive electrode uses a positive electrode pole piece whose density after coating is the lower limit of the coating accuracy, that is, the positive electrode surface density is 378-4=374g / m 2 The negative electrode uses a negative electrode whose density after coating is the upper limit of the coating accuracy, that is, the negative electrode surface density is 218+4=222g / m 2 The electrode is produced, and the resulting battery is the maximum NP ratio battery under the conventional production method. After production is completed, the battery performance is tested.

[0130] Through calculation, we know that:

[0131] After matching and winding according to comparative example 1, the actual NP ratio of the battery is: 1.093. The specific calculation process is as follows:

[0132] NP min1 =214*340*95%*99.71% / (382*171.6*96.6%*99.54%)=1.093

[0133] After matching and winding according to comparative example 2, the actual NP ratio of the battery is: 1.159. The specific calculation process is as follows:

[0134] NP max1 =222*340*95%*99.71% / (374*171.6*96.6%*99.54%)=1.159

[0135] Through the above calculation process, it can be known that the actual NP ratio range of the battery produced after matching winding according to the conventional production method is: 1.093-1.159.

[0136] The ideal NP ratio is calculated as:

[0137] NP 理想 =218*340*95%*99.71% / (378*171.6*96.6%*99.54%)=1.126

[0138] By comparing the NP ratio range of batteries produced by the method of the present invention, it can be found that the actual NP ratio range of the batteries produced by the method of the present invention is more concentrated. By using the method of the present invention, the actual NP ratio range of the manufactured batteries can be effectively made more concentrated and close to the ideal NP ratio, which has guiding significance for improving the accuracy of the NP ratio of lithium-ion batteries, product production stability and product performance.

[0139] In this embodiment, high temperature short circuit test comparison, first efficiency comparison, cycle retention ratio comparison and rate discharge performance of the prepared batteries were also carried out. Figure 5-Figure 8 As shown:

[0140] High temperature short circuit test comparison results are as follows Figure 5 As shown, it can be seen that the maximum temperature of the battery body of the battery prepared by the method of the present invention is similar to that of the battery of Comparative Example 2 during the high-temperature short-circuit process, and the maximum temperature of the battery body of the battery of Comparative Example 1 during the high-temperature short-circuit process is lower;

[0141] The first effect comparison bar chart is as follows Figure 6 As shown, it can be seen that the first effect of the battery made by the method of the present invention is higher than the first effect of the battery of Comparative Example 1-2;

[0142] The cycle comparison curve is as follows Figure 7 As shown in the figure, it can be seen that the cycle retention rate of the battery prepared by the method of the present invention is similar to the cycle retention rate of the battery in Comparative Example 2 and is better than the cycle retention rate of the battery in Comparative Example 1;

[0143] The ratio comparison curve is as follows: Figure 8 As shown in the figure, it can be seen that the rate discharge performance of the battery prepared by the method of the present invention is better than that of the battery in Comparative Example 1-2;

[0144] It is further explained that the method of the present invention can effectively make the actual NP ratio range of the manufactured battery more concentrated and close to the ideal NP ratio, which has guiding significance for improving the accuracy of the NP ratio of lithium-ion batteries, product production stability and product performance.

[0145] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0146] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for optimizing the NP ratio of a lithium-ion battery, characterized in that: The following steps are involved: S1. Determine the classification standards of positive and negative electrodes based on battery design information; S2. Use a sampler of a certain area and adopt the "nine-point sampling method - three samplings" to sample the positive and negative electrodes after coating, rolling and slitting according to the process requirements; S3. Number, weigh and record the corresponding electrode weights of the sampled positive and negative electrodes, calculate the average weight of the sampled electrodes, and mark the positive and negative electrode positions according to the positive and negative electrode classification standards; S4. Match and wind the positive and negative electrode sheets according to the set matching standards and matching principles based on the positive and negative electrode sheet positions.

2. The method for optimizing the NP ratio of a lithium-ion battery according to claim 1, characterized in that: In step S1, the calculation method for obtaining the positive and negative electrode classification standard is: Upper and lower limits of grade weight = (Z B *S+(Z+nQ)*S)*X*3 Among them, Z B is the surface density of the foil, S is the sampling area of ​​the sampler, Z is the limit surface density in the process, n is the error coefficient of the bin interval, Q is the error value of the bin interval, and X is the roller pressure correction coefficient; Roll pressure correction factor X is: X=1-Y Wherein, Y is the pole piece rolling extension rate, Y = (pole piece length after rolling - pole piece length before rolling) / pole piece length before rolling * 100%; The bin interval error coefficient n is the integer quotient of the coating machine accuracy and the bin interval error value; The grading order is carried out in descending order of surface density. Specifically: the maximum positive error value of coating accuracy is the upper limit value of the first gear in the grading standard, and the maximum negative error value of coating accuracy is the lower limit value of the last gear in the grading standard.

3. The method for optimizing the NP ratio of a lithium-ion battery according to claim 1, characterized in that: The specific content of step S2 is: The positive electrode sheets and the negative electrode sheets are coated, rolled and cut according to the process requirements; Take the positive and negative pole pieces from each small roll at the head, middle and tail positions respectively; After taking the slices, the taken electrode slices are divided into nine equal parts according to the area, and each of the nine equal parts is sampled according to the geometric center position.

4. The method for optimizing the NP ratio of a lithium-ion battery according to claim 1, characterized in that: The matching standard is that the positive electrode matched with the negative electrode should not be higher than the negative electrode. The matching principle is that electrodes of the same grade should be given priority, and electrodes of downgraded grade should be matched with the nearest electrode.

5. The method for optimizing the NP ratio of a lithium-ion battery according to claim 4, characterized in that: The maximum gear difference between the negative electrode plate and the matching positive electrode plate is 2 gears.

6. The method for optimizing the NP ratio of a lithium-ion battery according to claim 4, characterized in that: The NP ratio of the pole pieces of different gears is greater than the NP ratio of the pole pieces of the same gear.

7. A method for evaluating the NP ratio of a lithium-ion battery, characterized in that: When the negative electrode sheet and the positive electrode sheet are matched for use according to the method for optimizing the NP ratio of a lithium-ion battery as described in any one of claims 1 to 6, the NP ratio range of the positive and negative electrodes of the lithium-ion battery is: The minimum NP ratio when the same-level pole pieces are matched is: the NP ratio when the lower limit of the negative pole piece of the same level is matched with the upper limit of the positive pole piece of the same level; The maximum NP ratio when the differential pole pieces are matched is: the NP ratio when the upper limit pole piece of the high-gear negative pole piece is matched with the lower limit pole piece of the low-gear positive pole piece.

8. The method for evaluating the NP ratio of a lithium-ion battery according to claim 7, characterized in that: The minimum NP ratio when the pole pieces of the same gear are matched is as follows: When the negative electrode surface density - the positive electrode surface density < Q, the minimum NP ratio of the same-level pole pieces decreases as the level decreases. At this time, the minimum NP is the NP ratio of the lowest-level positive and negative pole pieces. When the negative electrode surface density - the positive electrode surface density > Q, the minimum NP ratio when the same-level pole pieces are matched increases as the gear decreases. At this time, the minimum NP is the NP ratio when the positive and negative pole pieces are matched at the highest level.

9. The method for evaluating the NP ratio of a lithium-ion battery according to claim 7, characterized in that: The maximum NP ratio when the differential pole piece is matched is as follows: When the positive electrode surface density - the negative electrode surface density > 2Q, the maximum NP ratio of the differential electrode piece matching decreases as the gear position decreases. At this time, the maximum NP is the NP ratio when the upper limit electrode piece of the highest gear negative electrode piece is matched with the lower limit electrode piece of the low gear positive electrode piece; When the positive electrode surface density - the negative electrode surface density is less than 2Q, the maximum NP ratio of the differential electrode piece increases as the gear position decreases. At this time, the maximum NP is the NP ratio of the upper limit electrode piece of the lowest gear negative electrode piece and the lower limit electrode piece of the low gear positive electrode piece.

10. A lithium ion battery, characterized in that: The lithium-ion battery is manufactured using the lithium-ion battery NP ratio optimization method described in any one of claims 1 to 6.

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