Method for detecting lithium precipitation of negative electrode of lithium ion battery

Abstract

The invention provides a method for detecting lithium precipitation of a negative electrode of a lithium ion battery. The lithium ion battery lithium precipitation detection method comprises the following steps: a to-be-detected lithium ion battery is repeatedly subjected to constant-current and constant-voltage charging and discharging processes, and the charging current in each round of charging and discharging process is greater than the charging current in the previous round of charging and discharging process; and establishing a current-time change curve of the battery in each charging process, and detecting the lithium precipitation condition of the negative electrode of the lithium ion battery to be detected according to the current-time change curve. According to the detection method provided by the invention, rapid lithium precipitation detection can be realized, the purpose can be achieved by detecting a single battery, the detection cost is low, the detection process is simple, and the method is suitable for large-batch battery detection.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries and relates to a method for detecting lithium deposition at a negative electrode of a lithium ion battery. Background Art

[0002] Lithium-ion batteries have become the most promising secondary batteries due to their significant advantages such as high specific energy density, long cycle life, high operating voltage, fast charging speed, low self-discharge rate, and no memory effect. With the widespread application of lithium-ion batteries in electronic products (including mobile phones, digital cameras and laptops, etc.), electric vehicles and other fields, the safety of lithium-ion batteries has also received more and more widespread attention.

[0003] In lithium-ion battery systems, negative electrode materials have a great impact on the overall performance of the battery. The industrialized negative electrode materials for lithium-ion batteries are mainly various carbon materials, including graphitized carbon materials and amorphous carbon materials, such as natural graphite, modified graphite, mesophase carbon microspheres, soft carbon and some hard carbon, etc. Other non-carbon negative electrode materials, including nitrides, silicon-based materials, tin-based materials, titanium-based materials, alloy materials, etc., have become research hotspots for seeking the next generation of high specific capacity and high energy density lithium-ion battery negative electrode materials.

[0004] When the reaction potential of carbon materials, silicon-based materials, tin-based materials, nitrides and transition metal oxides as negative electrode materials of lithium-ion batteries is close to the deposition potential of metallic lithium, lithium deposition is prone to occur at the negative electrode. Lithium deposition at the negative electrode of lithium-ion batteries occurs under conditions such as high rate, low temperature or overcharge. The main reason for lithium deposition is that the embedding reaction kinetics of lithium ions and the diffusion rate in the solid phase of the negative electrode material are reduced, polarization increases, resulting in a large negative electrode overpotential. When the negative electrode potential reaches the lithium deposition potential, lithium deposition and the formation of lithium dendrites will occur. The deposited lithium reacts with the electrolyte to consume active lithium, resulting in the loss of active lithium and the thickening of the surface SEI film, causing the capacity loss of the battery and the reduction of the battery life. The growth of negative electrode lithium dendrites and the formation of dead lithium can easily puncture the diaphragm and cause a short circuit between the positive and negative electrodes of the battery, thereby causing safety problems. Therefore, in order to ensure the normal use of the battery system and reduce safety risks, it is necessary to detect lithium deposition in the battery in a timely manner.

[0005] At present, there are several main methods for detecting lithium deposition at the negative electrode of lithium-ion batteries. One is to observe the negative electrode after disassembling the battery to determine whether lithium deposition occurs. This method is destructive and cannot detect the lithium deposition of the battery in real time. Another method is to assemble three electrodes and monitor the change of the negative electrode potential during the charging process through the three electrodes to determine whether lithium deposition occurs. This method requires the preparation of complex three electrodes, which will introduce and interfere with other factors, making it difficult to monitor lithium deposition and the repeatability is poor. There is also a physical detection method, which is to prepare a specific test battery for in-situ observation to determine whether lithium deposition occurs. However, the equipment for in-situ physical testing is expensive and difficult to operate. The in-situ observation device platform for dendrite growth requires different conditions, resulting in a lack of comparability and repeatability of the experimental results, and commercial lithium-ion batteries cannot be tested directly.

[0006] Therefore, it is urgently needed to provide a simple, feasible detection method that can detect the problem of battery lithium deposition in real time and accurately. Summary of the invention

[0007] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for detecting lithium deposition in the negative electrode of a lithium-ion battery. The detection method provided by the present invention can realize rapid lithium deposition detection, and can achieve the purpose by detecting a single battery, with low detection cost and simple detection process, and is suitable for large batches of battery detection.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for detecting lithium deposition in a negative electrode of a lithium ion battery, the method comprising the following steps:

[0010] The lithium-ion battery to be tested is repeatedly subjected to constant current and constant voltage charging and discharging processes, and the charging current in each round of charging and discharging process is greater than the charging current in the previous round of charging and discharging process;

[0011] The current-time variation curve of the battery during each round of charging is established, and the lithium plating condition of the negative electrode of the lithium-ion battery to be tested is detected based on the current-time variation curve.

[0012] The lithium ion battery provided by the present invention is a lithium ion battery that has undergone a conventional chemical composition and capacity determination procedure; and the charging and discharging process provided is a performance characterization process of first charging under constant current and constant voltage and then discharging.

[0013] The detection method provided by the present invention adopts different currents, which are charging currents that increase in sequence, to carry out constant current and constant voltage charging and discharging processes, thereby obtaining current-time variation curves under different charging rates, and determining whether lithium deposition occurs in the battery under the charging rate based on whether a characteristic peak exists in the current-time variation curve. The detection method is simple and rapid, thereby realizing lithium deposition detection of lithium-ion batteries under different charging rates, and the purpose can be achieved by detecting a single battery, and the detection cost is low.

[0014] Moreover, the detection method provided by the present invention requires a complete charging and discharging process in each round. If only the charging process is performed, it is impossible to realize the sequential increase of the charging current and achieve the purpose of detecting lithium deposition by detecting a single battery. At the same time, the detection method provided by the present invention increases the charging current in each round in sequence. If this rule is not adopted, it is difficult to obtain the exact critical point of lithium deposition.

[0015] Preferably, the charging current in each round of charging and discharging is independently 0.1 to 10C, for example, 0.1C, 0.2C, 0.5C, 1C, 1.5C, 2C, 2.25C, 2.5C, 2.75C, 3C, 3.25C, 3.5C, 4C, 4.5C, 5C, 6C, 7C, 8C, 9C or 10C.

[0016] Preferably, during each round of charging and discharging, the voltage range is 2.8 to 4.2 V, such as 2.8 V, 3 V, 3.3 V, 3.5 V, 3.8 V, 4 V or 4.2 V. The voltage range provided in this application can be adaptively selected by those skilled in the art according to different requirements.

[0017] Preferably, during the first round of charging and discharging, the charging current is 0.1 to 3C, for example, 0.1, 0.2, 0.25C, 0.5C, 0.75C, 1C, 1.25C, 1.5C, 1.75C, 2C, 2.25C, 2.5C, 2.75C or 3C.

[0018] In the detection method provided by the present invention, if the charging current in the first round of charge and discharge process is too large, it will affect the battery state, and further affect the judgment of the battery lithium deposition rate. In addition, too large a current may cause lithium deposition during the first charge of the battery, making it impossible to judge the exact critical point of lithium deposition of the battery.

[0019] Preferably, in the repeated charging and discharging process, the difference between the charging current in each round of charging and discharging process and the charging current in the previous round of charging and discharging process is independently 0.1 to 5C, for example, 0.1C, 0.2C, 0.5C, 1C, 1.5C, 2C, 2.25C, 2.5C, 2.75C, 3C, 3.25C, 3.5C, 4C, 4.5C or 5C, etc.

[0020] In the present invention, the difference in charging current during two adjacent rounds of charging and discharging may not be uniform, that is, it can be adaptively selected within the range of 0.1 to 5C.

[0021] Preferably, the discharge current in each round of charging and discharging is independently 0.1 to 5C, for example, 0.1C, 0.2C, 0.5C, 1C, 1.5C, 2C, 2.25C, 2.5C, 2.75C, 3C, 3.25C, 3.5C, 4C, 4.5C or 5C.

[0022] Preferably, the discharge current in each round of charging and discharging process remains consistent.

[0023] In the present invention, the discharge current in each round of charge and discharge process remains consistent, which can better realize the judgment of the lithium deposition state and the critical point of lithium deposition of the battery. If the discharge current in each round is different, it is easy for the battery to be in a different state during each round of battery charging, which will interfere with the judgment of the lithium deposition state of the battery in the next round of charge and discharge.

[0024] Preferably, the current-time variation curve of the battery in each round of charging is differentiated to obtain a processed current-time variation curve, and the lithium deposition condition of the lithium-ion battery to be tested is detected based on the processed current-time variation curve.

[0025] Preferably, when the processed current-time variation curve has a characteristic peak, it is determined that the negative electrode of the lithium ion battery to be tested has lithium deposition under the charging current; when the processed current-time variation curve does not have a characteristic peak, it is determined that the negative electrode of the lithium ion battery to be tested has not lithium deposition under the charging current.

[0026] Preferably, according to the characteristic peak of the processed current-time variation curve, the charging current value at which the characteristic peak appears for the first time is the critical point at which lithium deposition occurs at the negative electrode of the lithium-ion battery to be tested.

[0027] In the present invention, according to the provided lithium deposition detection method, the charging current is increased gradiently (i.e., it is increased by a fixed charging current difference), and when the battery is determined to have lithium deposition at a certain current, the current is the critical point of lithium deposition. The judgment method is simple and fast, easy to promote and operate, and the batteries of the same batch can be charged, disassembled, and mutually verified before and after the critical point current of lithium deposition is determined.

[0028] As a preferred technical solution, the lithium ion battery lithium deposition detection method comprises the following steps:

[0029] (1) The lithium-ion battery to be tested is charged at a charging current of 0.1 to 3C for the first round, and then discharged at a discharge current of 0.1 to 5C for the first round;

[0030] (2) In the next round of charging and discharging, the charging current is increased, and then the battery is discharged with the discharge current of the first round of discharging;

[0031] Repeat the process of step (2);

[0032] The difference between the charging current in each round of charging and discharging and the charging current in the previous round of charging and discharging is independently 0.1 to 5C;

[0033] Establishing a current-time variation curve of the battery during each round of charging, performing differentiation processing on the current-time variation curve of the battery during each round of charging to obtain a processed current-time variation curve;

[0034] When a characteristic peak appears in the current-time variation curve after treatment, it is determined that lithium deposition occurs at the negative electrode of the lithium ion battery to be tested under the charging current; when no characteristic peak appears in the current-time variation curve after treatment, it is determined that no lithium deposition occurs at the negative electrode of the lithium ion battery to be tested under the charging current; at the same time, the charging current value at which the characteristic peak appears for the first time is the critical point at which lithium deposition occurs at the negative electrode of the lithium ion battery to be tested.

[0035] It should be noted that the lithium ion battery provided by the present invention is commonly known to those skilled in the art.

[0036] For example, a lithium-ion battery includes a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte are all selected by conventional technology, and their preparation methods are also conventional technical means.

[0037] Optionally, the positive electrode includes a positive electrode collector and a positive electrode active material layer located on at least one side of the positive electrode collector, the positive electrode active material layer includes a positive electrode active material, a conductive agent and a binder, and the negative electrode includes a negative electrode collector and a negative electrode active material layer located on at least one side of the negative electrode collector (it may also be a pure metal negative electrode), the negative electrode active material includes a negative electrode active material, a conductive agent and a binder (it may also be a pure metal negative electrode).

[0038] The types of the above raw materials are not particularly limited. Any known substances can be used in the present application without violating the inventive concept of the present application.

[0039] Optionally, the positive electrode active material includes but is not limited to lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (LiNi x Mn y Co 1-x- y O2, referred to as NMC), lithium nickel cobalt aluminum oxide (LiNiCoAlO2, referred to as NCA), lithium manganese oxide (LiMn2O4), lithium manganese iron phosphate (LiMn x Fe 1-x PO4, referred to as LMFP), lithium vanadium phosphate (Li3V2(PO4)3), lithium vanadium phosphate (LiVOPO4), lithium iron phosphate (LiFePO4), lithium titanate (Li2TiO3) and one or more of lithium-rich manganese-based materials.

[0040] Optionally, the negative electrode active material includes graphite, non-graphite carbon and non-carbon-based graphite materials. In other embodiments, the negative electrode active material is a silicon-based negative electrode active material, which contains silicon, such as silicon alloys, silicon oxides or combinations thereof, which may also be mixed with graphite in some cases. In other embodiments, the negative electrode may include a carbonaceous-based negative electrode active material, which includes one or more of graphite, graphene, carbon nanotubes (CNTs) and combinations thereof. In another embodiment, the negative electrode active material includes one or more negative electrode active materials that accept lithium, such as lithium titanium oxide (Li4Ti5O 12 ), one or more transition metals (such as tin (Sn)), one or more metal oxides (such as vanadium oxide (V2O5), tin oxide (SnO), titanium dioxide (TiO2)), titanium niobium oxide (Ti x Nb y O z , where 0≤x≤2, 0≤y≤24 and 0≤z≤64), a metal alloy such as copper tin alloy (Cu6Sn5) and one or more metal sulfides such as iron sulfide (FeS).

[0041] Optionally, the positive electrode current collector and the negative electrode current collector are not particularly limited as long as they have conductivity without causing chemical changes in the battery. Specifically, copper, stainless steel, aluminum, nickel, titanium, or a metal current collector with a surface treated with carbon or other substances can be used.

[0042] Optionally, the binder is a component used to assist the bonding of active materials, conductive materials, etc. and to the current collector, and specifically may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber and fluororubber.

[0043] Conductive agents can be used to assist and improve the conductivity in secondary batteries, and there is no particular limitation as long as they have conductivity without causing chemical changes. Specifically, graphite, such as natural graphite or artificial graphite, carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers, such as carbon fibers and metal fibers, conductive tubes, such as carbon nanotubes, metal powders, such as fluorocarbon powders, aluminum powders, and nickel powders, conductive whiskers, such as zinc oxide and potassium titanate, conductive metal oxides, such as titanium oxide, and polyphenylene derivatives.

[0044] Alternatively, the separator separates the negative electrode from the positive electrode and provides a path for the movement of lithium ions. Any separator can be used without particular limitation, as long as it is a separator commonly used in secondary batteries. In particular, a separator having excellent electrolyte moisture content and low resistance to ion movement in the electrolyte is preferred. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer, or a laminated structure having two or more layers thereof. In addition, a typical porous nonwoven fabric can be used, for example, a nonwoven fabric formed of glass fiber, polyethylene terephthalate fiber, etc. having a high melting point. In addition, a coated separator comprising a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multilayer structure.

[0045] Optionally, the electrolyte solution includes an electrolyte salt and a solvent.

[0046] Optionally, the electrolyte salt includes but is not limited to one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate.

[0047] Optionally, the solvent includes but is not limited to one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0048] Optionally, the electrolyte further includes an additive, which may be a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive that can improve certain battery properties, for example, an additive that improves battery overcharge performance, an additive that improves battery high temperature or low temperature performance, etc. Without violating the inventive concept of the present application, any known type of additive can be applied to the present application. There are no special requirements for the mixing method of the additive, for example, it can be directly mixed with a conductive agent, an active substance, and a binder to form a mixture.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The detection method provided by the present invention adopts different currents, which are charging currents that increase in sequence, to carry out a charging and discharging process under constant current and constant voltage, thereby obtaining current-time variation curves under different charging rates, and determining whether lithium deposition occurs in the battery under the charging rate according to whether a characteristic peak exists in the current-time variation curve. The detection method is simple and quick to read, thereby realizing lithium deposition detection of lithium-ion batteries under different charging rates, and the purpose can be achieved by detecting a single battery, and the detection cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a current-time curve diagram of the lithium-ion battery provided in Example 1 during the charge and discharge process.

[0052] Figure 2 For Figure 1 The differential curve after differentiation processing.

[0053] Figure 3 This is a disassembly diagram of a lithium-ion battery after charging to 2.25C rate cutoff during the verification process provided in Example 1.

[0054] Figure 4 This is a disassembly diagram of a lithium-ion battery after charging to 2.5C rate cutoff during the verification process provided in Example 1.

[0055] Figure 5 This is a disassembly diagram of a lithium-ion battery after charging to 2.75C rate cutoff during the verification process provided in Example 1.

[0056] Figure 6 This is a current-time curve diagram of the lithium-ion battery provided in Example 2 during the charge and discharge process.

[0057] Figure 7 For Figure 6 The differential curve after differentiation processing.

[0058] Figure 8 This is a current-time curve diagram of the lithium-ion battery provided in Example 3 during the charge and discharge process.

[0059] Fig. 9 For Figure 8 The differential curve after differentiation processing.

[0060] Fig.10 This is a current-time curve diagram of the lithium-ion battery provided in Example 4 during the charge and discharge process.

[0061] Fig.11 For Fig.10 The differential curve after differentiation processing. DETAILED DESCRIPTION

[0062] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0063] Example 1

[0064] This embodiment provides a method for detecting lithium deposition at a negative electrode of a lithium ion battery, and the detection method is as follows:

[0065] In an environment of 25°C:

[0066] The lithium-ion battery (NCM523 / single-grain graphite) after the capacity conversion was first charged to 4.2V at a charging current of 0.2C, and then discharged to 2.8V at 1C;

[0067] After the first charge and discharge, charge to 4.2V at 1.5C, then charge at constant voltage until the current is less than 0.05C, and then discharge to 2.8V at 1C.

[0068] Continue to repeat the charging and discharging process. In each subsequent round of charging and discharging, the difference in charging current is 0.25C, and the voltage range is consistent with the previous one (that is, starting from the third round, the charging and discharging process is carried out with a charging current increase of 0.25C in each round, and the discharge current is kept at 1C);

[0069] The current-time curve of each round of constant voltage charging is established. In order to compare the current-time curve changes at different rates on the same graph, the current magnitude at different rates is moved up or down to different degrees, and the following is obtained: Figure 1 The charging time-current curves at different rates are shown in Figure 1 It can be seen that as the charging rate increases, there is no lithium precipitation characteristic peak at the beginning, until the characteristic peak begins to appear at 2.5C, and the subsequent rate lithium precipitation characteristic peak becomes more and more obvious, indicating that the lithium precipitation critical point of the lithium ion battery in this embodiment is 2.5C, but because the lithium precipitation reaction is weak at the lithium precipitation critical point, the characteristic peak is not obvious, and the data can be differentiated;

[0070] Will Figure 1 The current-time curve in the differential processing is carried out. For the convenience of curve viewing, the rate curve before and after lithium is selected to obtain Figure 2 ,from Figure 2 It can be clearly seen that the lithium-ion battery has a characteristic peak starting from 2.5C, indicating that the critical point of lithium deposition of the lithium-ion battery in this embodiment is 2.5C.

[0071] In order to verify the accuracy of the detection method provided in this embodiment, the same batch of lithium-ion batteries were used, that is, all materials, structures and preparation processes were exactly the same, one group of batteries were charged to 2.25C rate cutoff according to the previous test steps, one group was charged to 2.5C rate cutoff, and one group was charged to 2.75C rate cutoff, and then the batteries were disassembled.

[0072] The disassembly diagram of the battery after charging to 2.25C rate cutoff is as follows Figure 3 As shown, the disassembly diagram of the battery after charging to 2.5C rate is as follows Figure 4 As shown, the disassembly diagram of the battery after charging to 2.75C rate cutoff is as follows Figure 5 As shown, from Figures 3 to 5 It can be seen that when the batteries are charged to a rate of 2.25C and then disassembled, there is no obvious lithium deposition on the surface of the electrode. When the batteries are charged to a rate of 2.5C and then disassembled, slight lithium deposition occurs on the surface of the electrode. When the batteries are charged to a rate of 2.75C and then disassembled, the lithium deposition on the surface of the electrode is significantly aggravated, which proves the accuracy of the method.

[0073] Example 2

[0074] This embodiment provides a method for detecting lithium deposition at a negative electrode of a lithium ion battery, and the detection method is as follows:

[0075] In an environment of 25°C:

[0076] The lithium-ion battery (NCM523 / secondary graphite particles) after the chemical composition was charged to 4.2V at a charging current of 0.2C, and then discharged to 2.8V at 1C;

[0077] After the first charge and discharge, charge to 4.2V at 1.5C, then discharge to 2.8V at 1C;

[0078] Continue to repeat the charging and discharging process. In each subsequent round of charging and discharging, the difference in charging current is 0.25C, and the voltage range is consistent with the previous one (that is, starting from the third round, the charging and discharging process is carried out with a charging current increase of 0.25C in each round, and the discharge current is kept at 1C);

[0079] The current-time curve of each round of constant voltage charging is established. In order to compare the current-time curve changes at different rates on the same graph, the current magnitudes of the above curves at different rates are differentiated to move up or down to different degrees, and the following is obtained: Figure 6 The charging time-current curves at different rates are shown in Figure 6 It can be seen that as the charging rate increases, there is no lithium precipitation characteristic peak at the beginning, until the characteristic peak begins to appear at 3C, and the subsequent lithium precipitation characteristic peak becomes more and more obvious, indicating that the lithium precipitation critical point of the lithium ion battery in this embodiment is 3C, but because the lithium precipitation reaction is weak at the lithium precipitation critical point, the characteristic peak is not obvious, and the data can be differentiated;

[0080] Will Figure 6 The current-time curve in the differential processing is carried out. For the convenience of curve viewing, the rate curve before and after lithium is selected to obtain Figure 7 ,from Figure 7 It can be clearly seen that the lithium-ion battery has a characteristic peak starting from 3C, indicating that the critical point of lithium deposition of the lithium-ion battery in this embodiment is 3C, which is better than embodiment 1 and conforms to the fast charging and lithium deposition rules of the two negative electrodes.

[0081] Example 3

[0082] This embodiment provides a method for detecting lithium deposition at a negative electrode of a lithium ion battery, and the detection method is as follows:

[0083] In an environment of 25°C:

[0084] The lithium-ion battery (NCM523 / single-grain graphite, which is exactly the same as the battery in Example 1) after the capacity conversion was first charged to 4.2V at a charging current of 0.2C, and then discharged to 2.8V at 0.2C;

[0085] After the first charge and discharge, charge to 4.2V at 1.5C, then charge at constant voltage until the current is less than 0.05C, and then discharge to 2.8V at 1.5C.

[0086] Continue to repeat the charging and discharging process. In each subsequent round of charging and discharging, the difference in charging current is 0.25C, and the voltage range is consistent with the previous one (that is, starting from the third round, the charging current is increased by 0.25C in each round of charging and discharging, and the discharge current is consistent with the charging current in each round);

[0087] The current-time curve of each round of constant voltage charging is established. In order to compare the current-time curve changes at different rates on the same graph, the current magnitudes of the above curves at different rates are differentiated to move up or down to different degrees, and the following is obtained: Figure 8The charging time-current curves at different rates are shown in Figure 8 It can be seen that as the charging rate increases, there is no lithium precipitation characteristic peak at the beginning, but due to the gradual increase in the discharge current, the discharge is insufficient, and a characteristic peak begins to appear at 2.25C. The subsequent lithium precipitation characteristic peak becomes more and more obvious, indicating that the critical point of lithium precipitation of the lithium ion battery in this embodiment is 2.25C;

[0088] Will Figure 8 The current-time curve in the differential processing is carried out. For the convenience of curve viewing, the rate curve before and after lithium is selected to obtain Fig. 9 ,from Fig. 9 It can be clearly seen that the lithium-ion battery has a characteristic peak starting from 2.25C, indicating that the critical point of lithium deposition of the lithium-ion battery in this embodiment is 2.25C.

[0089] Comprehensive analysis Figure 1-Figure 3 and Figure 8-Figure 9 By comparison, it can be concluded that, in the control case of exactly the same battery, when the discharge current is inconsistent during each round of charging and discharging, the battery is in a different state during each round of charging, causing the battery lithium deposition phenomenon to occur earlier or later, interfering with the judgment of the battery's critical point of lithium deposition, resulting in poor accuracy of the test results.

[0090] Example 4

[0091] This embodiment provides a method for detecting lithium deposition at a negative electrode of a lithium ion battery, and the detection method is as follows:

[0092] In an environment of 25°C:

[0093] The lithium-ion battery (NCM523 / single-grain graphite) after the capacity conversion was first charged to 4.2V at a charging current of 3.25C, and then discharged to 2.8V at 1C;

[0094] After the first charge and discharge, charge to 4.2V at 3.5C, then charge at constant voltage until the current is less than 0.05C, and then discharge to 2.8V at 1C.

[0095] Continue to repeat the charging and discharging process. In each subsequent round of charging and discharging, the difference in charging current is 0.25C, and the voltage range is consistent with the previous one (that is, starting from the second round, the charging and discharging process is carried out with a charging current increase of 0.25C in each round, and the discharge current is kept at 1C);

[0096] The current-time curve of the constant voltage charging process in each round of constant voltage charging is established. In order to compare the current-time curve changes at different rates on the same graph, the current size of the above curve at different rates is differentiated to move up or down to different degrees, and the following is obtained: Fig.10 The charging time-current curves at different rates are shown in Fig.10 It can be seen that when charging at 3.25C, the characteristic peak of lithium deposition appears in the first charge, and the characteristic peak of lithium deposition becomes more and more obvious at the subsequent rates;

[0097] Will Fig.10 Differentiate the current-time curve in Fig.11 ,from Fig.11 It can also be clearly seen that the lithium-ion battery has a characteristic peak starting from 3.25C.

[0098] From the test results of Example 1 and Example 2, it can be seen that after verification, the detection method provided by the present invention has accurate results and a simple and fast detection process, and can achieve the purpose by detecting a single battery, and the detection cost is low; at the same time, the critical point of lithium deposition of the battery is also obtained, which provides strong support for the subsequent application of lithium-ion batteries.

[0099] It can be seen from the results of Example 1 and Example 3 that in the detection method provided by the present invention, if the discharge current in each round of discharge process is different, it will cause the battery to be in a different state during each round of battery charging, which will cause the battery lithium deposition phenomenon to occur earlier or later, and interfere with the judgment of the battery's lithium deposition critical point.

[0100] From the results of Example 1 and Example 4, it can be seen that in the detection method provided by the present invention, if the charging current in the first round of charging and discharging is too large, lithium deposition may occur during the initial charging, and the critical point of lithium deposition cannot be accurately obtained.

[0101] In summary, the detection method provided by the present invention adopts different currents, and the charging current is increased in sequence, and the charging and discharging process under constant current and constant voltage is carried out, thereby obtaining the current-time variation curve under different charging rates, and determining whether the battery has lithium deposition at the charging rate according to whether there is a characteristic peak in the current-time variation curve. The detection method is simple and fast to read, thereby realizing lithium deposition detection of lithium-ion batteries at different charging rates, and the purpose can be achieved by detecting a single battery, and the detection cost is low.

[0102] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for detecting lithium deposition at a negative electrode of a lithium ion battery, characterized in that: The lithium ion battery lithium deposition detection method comprises the following steps: The lithium-ion battery to be tested is repeatedly subjected to constant current and constant voltage charging and discharging processes, and the charging current in each round of charging and discharging process is greater than the charging current in the previous round of charging and discharging process; The current-time variation curve of the battery during each round of charging is established, and the lithium plating condition of the negative electrode of the lithium-ion battery to be tested is detected based on the current-time variation curve.

2. The method for detecting lithium deposition at the negative electrode of a lithium ion battery according to claim 1, wherein: The charging current in each round of charging and discharging process is independently 0.1 to 10C.

3. The method for detecting lithium deposition at the negative electrode of a lithium ion battery according to claim 1 or 2, wherein: During the first round of charging and discharging, the charging current is 0.1 to 3C; Preferably, during each round of charging and discharging, the voltage range is 2.8 to 4.2V.

4. The method for detecting lithium deposition at the negative electrode of a lithium ion battery according to any one of claims 1 to 3, characterized in that: During the repeated charging and discharging process, the difference between the charging current in each round of charging and discharging process and the charging current in the previous round of charging and discharging process is independently 0.1 to 5C.

5. The method for detecting lithium deposition at the negative electrode of a lithium ion battery according to any one of claims 1 to 4, characterized in that: The discharge current in each round of charging and discharging process is independently 0.1 to 5C.

6. The method for detecting lithium deposition at the negative electrode of a lithium ion battery according to any one of claims 1 to 5, characterized in that: The discharge current remains consistent during each cycle of charging and discharging.

7. The method for detecting lithium deposition at the negative electrode of a lithium ion battery according to any one of claims 1 to 6, characterized in that: The current-time variation curve of the battery in each round of charging is differentiated to obtain a processed current-time variation curve, and the lithium deposition situation of the lithium-ion battery to be tested is detected based on the processed current-time variation curve.

8. The method for detecting lithium deposition at the negative electrode of a lithium ion battery according to claim 7, wherein: When the processed current-time variation curve has a characteristic peak, it is determined that the negative electrode of the lithium ion battery to be tested has lithium deposition under the charging current; when the processed current-time variation curve does not have a characteristic peak, it is determined that the negative electrode of the lithium ion battery to be tested has not lithium deposition under the charging current.

9. The method for detecting lithium deposition at the negative electrode of a lithium ion battery according to claim 8, characterized in that: According to the characteristic peak of the processed current-time variation curve, the charging current value at which the characteristic peak appears for the first time is the critical point at which lithium deposition occurs at the negative electrode of the lithium-ion battery to be tested.

10. The method for detecting lithium deposition at the negative electrode of a lithium ion battery according to any one of claims 1 to 9, characterized in that: The lithium ion battery lithium deposition detection method comprises the following steps: (1) The lithium-ion battery to be tested is charged at a charging current of 0.1 to 3C for the first round, and then discharged at a discharge current of 0.1 to 5C for the first round; (2) In the next round of charging and discharging, the charging current is increased, and then the battery is discharged with the discharge current of the first round of discharging; Repeat the process of step (2); The difference between the charging current in each round of charging and discharging and the charging current in the previous round of charging and discharging is independently 0.1 to 5C; Establishing a current-time variation curve of the battery during each round of charging, performing differentiation processing on the current-time variation curve of the battery during each round of charging to obtain a processed current-time variation curve; When a characteristic peak appears in the current-time variation curve after treatment, it is determined that lithium deposition occurs at the negative electrode of the lithium ion battery to be tested under the charging current; when no characteristic peak appears in the current-time variation curve after treatment, it is determined that no lithium deposition occurs at the negative electrode of the lithium ion battery to be tested under the charging current; at the same time, the charging current value at which the characteristic peak appears for the first time is the critical point at which lithium deposition occurs at the negative electrode of the lithium ion battery to be tested.

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