Lithium Batteries and Electrical Devices

Abstract

The lithium battery and electrical device include a positive electrode piece, a negative electrode piece, and an electrolyte. The negative electrode piece includes a negative current collector and a negative electrode active material layer disposed on the surface of the negative current collector. The negative electrode active material layer includes a negative electrode active material. The surface density of one side of the negative electrode active material layer is A mg / cm. 2 , the thickness of the negative electrode active material layer is D μm, and the specific surface area of ​​the negative electrode active material is Sm 2 / g, and the viscosity of the electrolyte at 25±2°C is δmPa·sec. The negative electrode piece and the electrolyte are in a state where the following relationship exists: 1≦(δ×A 2 ) / (D×S)≦15.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This disclosure claims priority to Chinese Patent Application No. 202211169618.1, filed on September 26, 2022, entitled "LITHIUM BATTERY AND ELECTRICAL DEVICE," which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates to the technical field of lithium batteries, and in particular to lithium batteries and electrical devices. [Background technology]

[0003] With the development of lithium batteries, the demands on their performance are increasing. In particular, the demand for battery energy density is becoming increasingly high. In the industry, battery energy density is generally improved by increasing the packing density of the negative electrode plate. However, this often leads to difficulties in the complete penetration of the electrolyte into the negative electrode active material, resulting in insufficient uniformity of the solid electrolyte interface (SEI) film, ultimately leading to increased negative electrode impedance, reduced dynamic performance, and even severe lithium deposition or abnormal black spots / areas on the negative electrode plate. These issues cause a rapid decline in capacity retention during the battery cycling process, seriously affecting the battery's normal performance. Furthermore, at low temperatures, the lithium ion migration rate slows and the viscosity of the electrolyte increases. When the electrolyte cannot completely penetrate the negative electrode active material, the battery polarization becomes significantly greater during the discharge process at low temperatures, resulting in a significant deterioration of the battery's low-temperature performance. Summary of the Invention [Problem to be solved by the invention]

[0004] Although optimization efforts are being made on the compressed density of the negative electrode plate, the particle size of the electrode active material, and the composition of the electrolyte, the balance between the various factors mentioned above has not yet been determined, and there are limits to the improvement of battery performance. [Means for solving the problem]

[0005] In view of this, the present disclosure provides a lithium battery and an electric device, and by controlling the ratio coefficient between the parameters of the negative electrode plate and the parameters of the electrolyte within a certain range, it is possible to effectively ensure that the battery has excellent room temperature cycle performance and excellent low temperature performance.

[0006] In a first aspect, the present disclosure provides a lithium battery. The lithium battery includes a positive electrode plate, a negative electrode plate, and an electrolyte. The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on a surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The surface density of one side of the negative electrode active material layer is A mg / cm. 2 , the thickness of the negative electrode active material layer is D μm, and the specific surface area of ​​the negative electrode active material is Sm 2 / g, and the viscosity of the electrolyte at 25±2°C is δmPa·sec. The negative electrode plate and the electrolyte satisfy the following relationship: 1≦(δ×A 2 ) / (D×S)≦15.

[0007] By controlling the ratio coefficients of the surface density of one side of the negative electrode active material layer, the thickness of the negative electrode active material layer, the specific surface area of ​​the negative electrode active material, and the viscosity of the electrolyte within a certain range, the electrolyte can sufficiently penetrate the negative electrode active material through a balanced relationship between various parameters, thereby promoting more uniform growth of the SEI film on the surface of the negative electrode plate and promoting uniform dispersion of active lithium ions in the negative electrode plate. As a result, the battery can have a high capacity retention rate during room temperature cycling, a low expansion rate during room temperature cycling, and excellent low-temperature performance.

[0008] In some embodiments, A and D satisfy the following relationship: 1.6≦(10A) / D≦1.9.

[0009] In some embodiments, A is in the range of 6≦A≦15.

[0010] D is in the range of 40≦D≦90 in some embodiments.

[0011] In some embodiments, S is in the range 0.5≦S≦5.

[0012] In some embodiments, δ is in the range 3≦δ≦5.

[0013] The electrolyte, in some embodiments, comprises an organic solvent, a lithium salt, and an additive.

[0014] The organic solvent, in some embodiments, comprises at least one of a linear carbonate, a carboxylate, and a cyclic carbonate.

[0015] The lithium salt, in some embodiments, comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, lithium difluoro(oxalato)borate, and lithium bis(oxalato)borate.

[0016] The additive, in some embodiments, comprises at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3,6-hexanetricarbonitrile, glyceryl trinitrate, 1,2-bis(cyanoethoxy)ethane, 1,4-dicyano-2-butene, fumaronitrile, succinonitrile, adipodinitrile, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

[0017] In a second aspect, the present disclosure provides an electric device comprising the lithium battery according to the first aspect.

[0018] Due to the use of lithium batteries, the batteries of the electrical devices have a long battery life, excellent cycle performance, and high safety performance. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic structural diagram of a lithium battery according to an embodiment of the present disclosure; FIG. [Figure 2] 1 is a schematic structural diagram of an electrical device according to an embodiment of the present disclosure; DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of the present disclosure provides a lithium battery. As shown in FIG. 1 , the lithium battery 10 includes a positive electrode plate 110, a negative electrode plate 120, and an electrolyte 130. The negative electrode plate 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 disposed on the surface of the negative electrode current collector 121. The negative electrode active material layer includes a negative electrode active material. The surface density of one side of the negative electrode active material layer is A mg / cm 2 , the thickness of the negative electrode active material layer is D μm, and the specific surface area of ​​the negative electrode active material is Sm 2 / g, and the viscosity of the electrolyte at 25±2°C is δmPa·sec. The negative electrode plate and the electrolyte satisfy the following relationship:

number

[0021] For convenience of explanation,

number

[0022] It is understood that the influence of the above various parameters on the performance of the battery is diverse and difficult to quantify. However, through a series of studies, the applicant has determined that by defining the quantitative relationship between the above parameters A, D, S, and δ, the ratio coefficient M((δ×A 2We found that the relationship M (D × S) / (D × S) is defined as the ratio of the negative electrode active material layer to the negative electrode active material layer. M can reflect the comprehensive influence of various factors in the negative electrode active material layer and the viscosity of the electrolyte on the battery's cycling performance and lithium deposition. By controlling the M value between 1 and 15, the negative electrode plate can have a high compaction density and can be fully penetrated by the electrolyte. As a result, a stable and uniform SEI film can be formed at the interface of the negative electrode plate during the initial charge / discharge cycle of the battery, promoting the uniform distribution of active lithium ions within the negative electrode plate and allowing them to transport rapidly through the electrolyte. As a result, the capacity retention rate during the room-temperature cycling process of the battery is improved, the expansion rate during the room-temperature cycling process of the battery is reduced, the low-temperature performance of the battery is improved, and lithium deposition on the negative electrode is suppressed.

[0023] In general, a negative electrode plate for a battery often has a negative electrode active material layer disposed on two opposing side surfaces of a negative electrode current collector. In the present disclosure, a negative electrode active material layer having a thickness of D μm means that the thickness of the negative electrode active material layer on one side surface of the negative electrode current collector is D μm. When a negative electrode plate has negative electrode active material layers on two opposing side surfaces, the ratio coefficient M between the viscosity of the negative electrode active material layers on both side surfaces and the viscosity of the electrolyte is in the range of 1 to 15.

[0024] 1, a positive electrode plate 110 includes a positive electrode current collector 111 and a positive electrode active material layer 112 disposed on a surface of the positive electrode current collector 111. The positive electrode active material layer 112 includes a positive electrode active material.

[0025] A and D, in some embodiments of the present disclosure, are represented by the following relationship:

number

[0026] In some embodiments of the present disclosure, the thickness D μm of the negative electrode active material layer satisfies 40≦D≦90. That is, the thickness of the negative electrode active material layer is in the range of 40 μm to 90 μm. By using a thickness of the negative electrode active material layer controlled within this range in combination with the areal density A of one side, the compressed density of the negative electrode active material layer can be controlled within a suitable range, thereby allowing the electrolyte to completely permeate the negative electrode active material and facilitating the transport of active lithium ions in the negative electrode plate. When M is within the appropriate range, excellent overall performance of the battery is guaranteed. The thickness of the negative electrode active material layer may be, for example, 40 μm, 41.5 μm, 42.5 μm, 45 μm, 47.5 μm, 50 μm, 52.5 μm, 55 μm, 56 μm, 57.5 μm, 60 μm, 62.5 μm, 65 μm, 67.5 μm, 70 μm, 72.5 μm, 75 μm, 77.5 μm, 80 μm, 82.5 μm, 85 μm, 87.5 μm, or 90 μm.

[0027] In some embodiments of the present disclosure, the areal density A mg / cm of one side of the negative electrode active material layer 2 That is, the surface density of one side surface of the negative electrode active material layer is 6 mg / cm 2 ~15mg / cm 2 The surface density of one side of the negative electrode active material layer is, for example, 6.1 mg / cm 2 , 6.5 mg / cm 2 , 7 mg / cm 2 , 7.3 mg / cm 2, 7.5 mg / cm 2 , 8 mg / cm 2 , 8.1 mg / cm 2 , 8.5 mg / cm 2 , 9 mg / cm 2 , 9.5 mg / cm 2 , 9.6 mg / cm 2 , 10 mg / cm 2 , 10.5 mg / cm 2 , 11 mg / cm 2 , 11.5 mg / cm 2 , 12 mg / cm 2 , 12.5 mg / cm 2 , 13 mg / cm 2 , 13.5 mg / cm 2 , 14 mg / cm 2 , 14.5 mg / cm 2 , or 15 mg / cm 2 Similarly, when the areal density A of one side surface of the negative electrode active material is controlled to be within the above range, the negative electrode active material layer is controlled to have a high compressed density in combination with the thickness D of the negative electrode active material layer, and thus the battery has excellent overall performance.

[0028] In some embodiments of the present disclosure, the specific surface area Sm 2 / g satisfies 0.5≦S≦5. That is, the specific surface area of ​​the negative electrode active material is 0.5 m 2 / g~5m 2 The specific surface area of ​​the negative electrode active material is in the range of, for example, 0.5 m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g, 2.1m2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 3m 2 / g, 3.1m 2 / g, 3.2m 2 / g, 3.3m 2 / g, 3.4m 2 / g, 3.5m 2 / g, 3.6m 2 / g, 3.7m 2 / g, 3.8m 2 / g, 3.9m 2 / g, 4.0m 2 / g, 4.1m 2 / g, 4.2m 2 / g, 4.3m 2 / g, 4.4m 2 / g, 4.5m 2 / g, 4.6m 2 / g, 4.7m 2 / g, 4.8m 2 / g, 4.9m 2 / g, or 5.0m 2 / g. In some embodiments of the present disclosure, the specific surface area of ​​the negative electrode active material can be measured using the BET method. For example, a sample tube is weighed on a 1 / 10,000 balance, and the weight of the empty sample tube is recorded. Then, approximately 1 g of sample is added to the sample tube, weighed on the 1 / 10,000 balance, the weight is recorded, and the weight of the sample is calculated. The sample tube containing the sample is degassed at 200°C for 120 minutes in a specific surface adsorption analyzer (e.g., BSD-PS). The sample tube is removed and weighed, and the weight of the degassed sample is calculated. The sample tube containing the sample is then subjected to an adsorption and desorption test in a liquid nitrogen-cooled bath (adsorbate is nitrogen) in the specific surface adsorption analyzer, and the BET specific surface area of ​​the sample is calculated using the BET multi-point method. It should be understood that the above examples are merely illustrative of the technical solutions of the present disclosure and are not intended to be limitations of the present disclosure. The relevant details of the measurement method can be adjusted according to actual needs. In addition, the measurement method of the specific surface area is not limited in this disclosure, and other feasible methods can be used for actual measurement. When the negative electrode active material has a suitable specific surface area, the diffusion path of active lithium ions inside the negative electrode active material particles can be controlled to be short, resulting in a small negative electrode impedance. Furthermore, the number of active sites on the surface of the negative electrode active material can also be controlled within a suitable range to control the electrolyte consumption rate within a suitable range, reduce the loss of active lithium ions during the battery cycling process, and further control the battery to have a high capacity retention rate and excellent cycling performance. Furthermore, the specific surface area of ​​the negative electrode active material is controlled within an appropriate range, i.e., the particle size of the negative electrode active material particles is controlled within an appropriate range. With regard to the negative electrode plate fabrication process, an appropriate particle size can reduce the risk of the negative electrode active particles being crushed by excessive pressure during the negative electrode plate rolling process and promote the formation of a negative electrode plate with a high packed density.

[0029] In some embodiments of the present disclosure, the electrolyte includes a lithium salt, an organic solvent, and an additive. In some embodiments, the organic solvent includes at least one of a linear carbonate, a carboxylate, and a cyclic carbonate, but is not limited to these. The cyclic carbonate includes at least one of a cyclic ethylene carbonate, a cyclic propylene carbonate, a cyclic haloethylene carbonate, and a cyclic halopropylene carbonate, but is not limited to these. The linear carbonate includes at least one of a dimethyl carbonate, an ethyl methyl carbonate, a diethyl carbonate, a halogenated dimethyl carbonate, a halogenated ethyl methyl carbonate, and a halogenated diethyl carbonate, but is not limited to these. Carboxylate includes, but is not limited to, at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, ethyl haloacetate, ethyl halopropionate, propyl halopropionate, butyl halopropionate, and amyl halopropionate.

[0030] Cyclic carbonates have high viscosity, which can promote the dissolution of lithium salts in the electrolyte and ensure excellent conductivity of the electrolyte. Linear carbonates and carboxylates are low-viscosity organic solvents, and their presence reduces the overall viscosity of the electrolyte, ensuring excellent fluidity and improving the electrolyte's permeability. However, the oxidation resistance of low-viscosity organic solvents commonly used in the art is relatively poor. To avoid gas generation caused by the decomposition of excess low-viscosity organic solvents at high temperatures, the amount of low-viscosity organic solvent must be controlled to effectively reduce the risk of gas generation during storage at high temperatures or during charge / discharge processes. More importantly, the viscosity of the electrolyte must be controlled within a suitable range to ensure excellent permeability. In some specific embodiments, the organic solvent includes at least one of linear carbonates, carboxylates, and cyclic carbonates. In this case, the electrolyte will have better overall performance.

[0031] The lithium salt in the electrolyte, in some embodiments of the present disclosure, includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI, molecular formula LiN(SOCF)), lithium perchlorate (LiClO), lithium difluoro(oxalato)borate (LiODFB), and lithium bis(oxalato)borate (LiBOB).

[0032] In some embodiments of the present disclosure, the additive in the electrolyte solution includes at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3,6-hexanetricarbonitrile, glyceryl trinitrate, 1,2-bis(cyanoethoxy)ethane, 1,4-dicyano-2-butene, fumaronitrile, succinonitrile, adipoditrile, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate. Among the additives, fluoroethylene carbonate, vinylene carbonate, and 1,3-propane sultone can be used as negative electrode film-forming additives to promote the rapid formation of an SEI film on the surface of the negative electrode plate. The nitrile substance reacts with trace amounts of water after the electrolyte is injected into the battery to form an amide, reducing the risk of gas generation caused by decomposition of the organic solvent in the electrolyte at high temperatures, and forming a complex with metal ions (e.g., cobalt ions) that may be eluted from the positive electrode plate, thereby reducing the adhesion of metal ions to the surface of the negative electrode plate. In the present disclosure, the types and amounts of the additives are not limited and can be selected by those skilled in the art according to actual needs.

[0033] In some embodiments of the present disclosure, the viscosity δ mPa·sec of the electrolyte at 25±2°C satisfies 3≦δ≦5. That is, the viscosity of the electrolyte at 25±2°C is in the range of 3 mPa·sec to 5 mPa·sec. The viscosity of the electrolyte at 25±2°C is, for example, 3 mPa·sec, 3.1 mPa·sec, 3.2 mPa·sec, 3.3 mPa·sec, 3.4 mPa·sec, 3.5 mPa·sec, 3.6 mPa·sec, 3.7 mPa·sec, 3.8 mPa·sec, 3.9 mPa·sec, 4.0 mPa·sec, 4.1 mPa·sec, 4.2 mPa·sec, 4.3 mPa·sec, 4.4 mPa·sec, 4.5 mPa·sec, 4.6 mPa·sec, 4.7 mPa·sec, 4.8 mPa·sec, 4.9 mPa·sec, or 5.0 mPa·sec. From the viewpoint of fluid engineering, the electrolyte has a suitable viscosity throughout, which is beneficial for the flow of the electrolyte in the negative electrode active material layer and promotes complete penetration into the negative electrode active material, thereby reducing the risk of lithium deposition, reducing the impedance of the battery, and improving the low-temperature performance of the battery.

[0034] In embodiments of the present disclosure, the negative electrode active material may include, but is not limited to, one or more of a carbon material, a silicon-based material, a tin-based material, and lithium titanate. Carbon materials include one or more of soft carbon, hard carbon, carbon fiber, graphitized carbon microspheres, artificial graphite, and natural graphite. Silicon-based materials include one or more of elemental silicon, silicon alloys, silicon oxides, silicon-carbon composites, silicon carbide, and the like. Tin-based materials include one or more of elemental tin, tin oxide, tin-based alloys, tin-carbon compounds, and the like.

[0035] In an embodiment of the present disclosure, the negative electrode active material layer further includes a binder. The negative electrode active material layer may further include a conductive agent in some cases. The binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylonitrile (PAN), polyacrylates (such as polymethyl methacrylate, polymethyl acrylate, and polyethyl acrylate), polyolefins (such as polypropylene and polyethylene), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), and sodium alginate. The first conductive agent and the second conductive agent may be one or more independently selected from conductive carbon black (such as acetylene black, ketjen black, Supper P, and 350G carbon black), furnace black, carbon fiber, carbon nanotubes, and graphene. However, the present disclosure is not limited thereto. The current collector (specifically, the negative electrode current collector) carrying the negative electrode active material may include, but is not limited to, copper foil, stainless steel foil, copper alloy foil, carbon-coated copper foil, or copper-plated film.

[0036] The negative electrode plate is obtained by applying a negative electrode suspension containing a negative electrode active material, a binder, and an optional conductive agent to a current collector, drying the suspension, and rolling the current collector. The current collector may be coated on one or both surfaces. In other words, the negative electrode active material layer may be formed on one surface of the current collector, or on two opposing side surfaces of the negative electrode current collector. When the negative electrode current collector is coated on both surfaces, the ratio coefficient M of the negative electrode active material layer to the viscosity of the electrolyte on both sides is within the above-mentioned range.

[0037] In some embodiments of the present disclosure, as shown in FIG. 1 , the lithium battery 10 also includes a separator 140 located between the positive plate 110 and the negative plate 120. The positive electrode active material in the positive plate is a material into which lithium ions can be reversibly deintercalated and intercalated. For lithium batteries, the positive electrode active material may include, but is not limited to, one or more of lithium monoxides (such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide), lithium binary oxides (such as lithium nickel manganese oxide, lithium nickel cobalt oxide, and lithium cobalt manganese oxide), lithium ternary oxides (such as lithium nickel cobalt manganese oxide ternary materials or lithium nickel cobalt aluminum oxide ternary materials), lithium multi-element oxides, and lithium-containing phosphates (such as lithium iron phosphate and lithium manganese iron phosphate). The separator can be made of any of the separator materials used in existing batteries. The separator may include, by way of example and not limitation, a polymer separator such as a monolayer polypropylene (PP) film, a monolayer polyethylene (PE) film, a two-layer PP / PE film, a two-layer PP / PP film, and a three-layer PP / PE / PP film, or a nonwoven fabric.

[0038] An embodiment of the present disclosure further provides an electric device 1, which includes a lithium battery 10 according to an embodiment of the present disclosure, as shown in FIG.

[0039] In the present disclosure, there is no particular limitation on electrical devices that use lithium batteries, including, but not limited to, mobile phones, laptops, tablet computers, computers with stylus input, portable fax machines, portable copiers, portable printers, walkie-talkies, video recorders, cameras, televisions, radios, portable audio recorders, portable CD players, minidiscs, e-book players, electronic organizers, wearable devices (such as smart watches, smart bracelets, headphones, and Bluetooth headsets), portable vacuum cleaners, calculators, memory cards, emergency power supplies, vehicles, motorcycles, bicycles (such as electrically assisted bicycles), lighting equipment (such as flashlights), toys, game consoles, watches, power tools, large household batteries, and lithium ion capacitors.

[0040] Due to the use of lithium batteries, the batteries of the electrical devices have a long battery life, excellent cycle performance, and high safety performance.

[0041] The technical solutions of the present disclosure are further detailed in some embodiments.

[0042] The lithium batteries of the examples and comparative examples of the present disclosure were fabricated as follows.

[0043] (1) Preparation of electrolyte A solution of LiPF6 in an organic solvent was prepared in an argon-filled glove box with a water content of <1 ppm and an oxygen content of <1 ppm and used as the electrolyte. The organic solvent was a mixture of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC). The viscosity of the electrolyte was adjusted by adjusting the content of PC and DEC to finally obtain the electrolyte required for each example and comparative example. Fluoroethylene carbonate (FEC), an anode film-forming additive, was also added to the electrolyte. The viscosity of each electrolyte was tested at 25 °C using a rheometer (Anton Paar MCR92). To obtain viscosity curves at various shear rates, the electrolyte was sheared at a constant temperature of 25 °C at shear rates set by the instrument from 0.1 s to 300 s. The viscosity data at a shear rate of 100 ± 3 s was used as the viscosity value of the electrolyte.

[0044] (2) Preparation of the positive electrode plate The cathode active material, lithium cobalt oxide (LiCoO2), conductive agent, carbon nanotubes (CNT), and binder, polyvinylidene fluoride, were mixed in a weight ratio of 95:2:3, then transferred to the solvent, N-methylpyrrolidone (NMP), and thoroughly stirred in a vacuum mixer to obtain a cathode paste. The cathode suspension was evenly applied to an aluminum foil cathode current collector, dried at 85°C, rolled, cut, and dried under vacuum at 85°C for 4 hours to obtain a cathode plate.

[0045] (3) Preparation of negative electrode plate The negative electrode active material, graphite with a certain range of specific surface area, the binder, styrene butadiene rubber (SBR), and the binder, sodium carboxymethyl cellulose (CMC), were added to an appropriate amount of deionized water in a weight ratio of 95:2:3, mixed, and thoroughly stirred to obtain a negative electrode suspension. The negative electrode suspension was evenly applied to a copper foil negative electrode current collector, dried, rolled, and cut to obtain a negative electrode plate. Two opposing sides of some negative electrode current collectors had negative electrode active material layers. For the same negative electrode plate, the areal density (A mg / cm) of one of the two opposing negative electrode active material layers on each side was calculated. 2and the thickness D μm of the negative electrode active material layer on one side surface are the same.

[0046] (4) Fabrication of lithium batteries In a glove box, the fabricated positive electrode plate, separator (polyethylene film), and negative electrode plate were stacked, wound, placed in an outer foil, and dried to obtain a wound battery core. The separator was positioned between the positive electrode plate and the negative electrode plate to isolate them. The negative electrode plate located at the front or rear end of the alternatingly wound positive and negative electrode plates had a negative electrode active material layer on one side, while the remaining negative electrode plates had negative electrode active material layers on both opposing sides. The electrolyte solution fabricated in step (1) was injected into the dried, unfinished battery, followed by vacuum packaging, standing, chemical formation, shaping, and other processes to fabricate a lithium battery. The various example batteries are designated S1 to S28, and the various comparative example batteries are designated DS1 to DS4.

[0047] It should be understood that the order in which the operations involved in fabricating a lithium battery are performed is not limited to this disclosure. For example, operations (1), (2), and (3) may be performed simultaneously or in a different order than described herein.

[0048] The parameters of the lithium batteries in the various examples and comparative examples are summarized in Table 1.

[0049] The following performance tests were carried out on the batteries fabricated as each of the examples and comparative examples. Note that in the following performance tests, comparative analysis was carried out under the condition that the ratio of the reversible surface capacity of the negative electrode to the reversible surface capacity of the positive electrode (negative / positive, N / P) of various batteries was the same.

[0050] (1) Room temperature cycle test Five batteries from each example or comparative example were tested. The batteries were charged at room temperature (25±3°C) with a constant current of 1C to 4.45V, then charged at a constant voltage of 0.05C from 4.45V, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to 3.0V, allowed to stand for 5 minutes. This constituted one cycle. The capacity retention and expansion rate (thickness at the 1000th full charge / thickness at the first full charge) after 1000 cycles at room temperature were recorded for each battery. The average capacity retention and expansion rate after 1000 cycles at room temperature for each battery group were calculated. The results are summarized in Table 2 below. The test results for batteries that did not reach 1000 cycles were recorded as "NG." The expansion rate at room temperature for batteries that did not reach 1000 cycles was the expansion rate of the battery after the final cycle.

[0051] (2) Lithium deposition test after 20 cycles at 0°C Three batteries from each example or comparative example were tested. After standing at 0°C for 2 hours, the batteries were charged at a constant current of 0.5C to 4.45V, then charged at a constant voltage of 0.05C from 4.45V, held for 5 minutes, and then discharged at a constant current of 1C to 3.0V, held for 5 minutes. This constituted one cycle. After 20 cycles, the batteries were fully charged according to the above conditions and then disassembled in an inert atmosphere in a glove box. The lithium deposition on the surface of the negative electrode plate was recorded. The lithium deposition results for each battery group are summarized in Table 2 below.

[0052] (3) Battery discharge capacity retention test at -20°C Three batteries from each example or comparative example were tested. The batteries were charged at room temperature (25±3°C) with a constant current of 0.2C to 4.45V, then charged at a constant voltage of 0.05C from 4.45V, allowed to stand for 5 minutes, and then discharged at a constant current of 0.2C to 3.0V and allowed to stand for 5 minutes. The discharge capacity at 0.2C at room temperature was recorded as the initial capacity of the battery. The batteries were then charged at a constant current of 0.2C to 4.45V, then charged at a constant voltage of 0.05C from 4.45V, and allowed to stand for 5 minutes. The batteries were then allowed to stand at -20°C for 2 hours, and then discharged at a constant current of 0.2C to 3.0V. The discharge capacity of the batteries at 0.2C at -20°C was recorded.

[0053] Battery discharge capacity at -20°C = (discharge capacity at 0.2C at -20°C / initial battery capacity) x 100%. The average discharge capacity retention rate at -20°C for each battery group was calculated. The results are summarized in Table 2 below.

[0054] [Table 1]

[0055] [Table 2]

[0056] From the battery parameters in Table 1 and the battery performance in Table 2, it can be seen that when the ratio coefficient M between the composition of the negative electrode plate and the viscosity δ of the electrolyte of a lithium battery is in the range of 1 to 15, the lithium battery exhibits excellent room-temperature cycling performance, high capacity retention, and low battery thickness expansion. Furthermore, the low-temperature performance of the battery is also excellent. Slight lithium deposition on the negative electrode plate after 20 cycles at 0°C due to the edge effect of the negative electrode plate is acceptable and does not significantly affect the low-temperature performance of the battery. However, when the M value of the battery is higher or lower than the limit value specified in this disclosure (comparative batteries DS1 to DS4), the battery expansion rate during room-temperature cycling is very high and the safety performance is not very good. DS1 to DS3 even failed the room-temperature 1,000-cycle test, and the comparative battery exhibited severe lithium deposition after 20 low-temperature cycles, clearly demonstrating the inability of the comparative battery to operate stably for long periods at room and low temperatures.

[0057] Furthermore, in the batteries S8 and S7 of the example, if other parameters remain unchanged, the areal density A of one side of the negative electrode active material is 6 mg / cm 2 ~15mg / cm 2It can be seen that the cycle performance of battery (S7) when the surface density of one side is within the preferred range is superior to the cycle performance of battery (S8) of the Example when the surface density of one side is not within the preferred range. Similarly, a comparison of batteries S9 and S4 of the Example shows that, if other parameters remain unchanged, the thickness D of the negative electrode active material layer of S4 is within the preferred range of 40 μm to 90 μm, and the A value of battery S4 is smaller than the A value of battery S9, which indicates that the room temperature cycle performance and low-temperature discharge capacity retention rate of the battery are improved. As can be seen from batteries S18 to S19 and S12 to S17 of the Example, if other parameters remain unchanged, the specific surface area S of the negative electrode active material particles is 0.5 m 2 / g~5m 2 / g is in the preferred range, the overall performance of the battery is better. In particular, the expansion rate of batteries S12 to S17 is relatively low even after 1000 cycles at room temperature.

[0058] In addition, a comparison of the example batteries S24 and S28 with the batteries S21-S23 and S25-S27 shows that, with other parameters remaining unchanged, the overall performance of the example batteries is excellent when the viscosity of the electrolyte in the example batteries is in the preferred range of 3 mPa·sec to 5 mPa·sec. In particular, the expansion rates of the batteries S21-S23 and S25-S27 are relatively low even after 1000 cycles at room temperature, reducing the risk of lithium precipitation in the batteries and allowing the low-temperature performance to be maintained at a high level.

[0059] Regardless of whether the above parameters A, D, S, and δ are within the preferred ranges of the present disclosure, if the ratio coefficient M of the various parameters is within the range of 1 to 15 specified in the present disclosure, the battery performance will be improved by M((δ×A 2 The battery performance is clearly superior to that of the comparative batteries DS1 to DS4, whose values ​​of (D×S) / (D×S)) are not within the range of 1-15.

[0060] The exemplary embodiments of the present disclosure have been described above. It should be noted that without departing from the principle of the present disclosure, some improvements and modifications may be made by those skilled in the art, and they shall fall within the protection scope of the present disclosure. [Explanation of symbols]

[0061] 1 Electrical Devices 10. Lithium battery 110 Positive electrode plate 111 Positive electrode current collector 112 Cathode active material layer 120 negative electrode plate 121 Negative electrode current collector 122 Negative electrode active material layer 130 Electrolyte 140 Separator

Claims

1. A lithium battery (10) comprising a positive electrode plate (110), a negative electrode plate (120), and an electrolyte (130), wherein the negative electrode plate comprises a negative electrode current collector (121) and a negative electrode active material layer (122) disposed on the surface of the negative electrode current collector, the negative electrode active material layer containing a negative electrode active material, and the areal density of one side surface of the negative electrode active material layer is A mg / cm ２ the thickness of the negative electrode active material layer is D μm, and the specific surface area of ​​the negative electrode active material is Sm ２ / g, the viscosity of the electrolyte at 25±2° C. is δ mPa·sec, and the negative electrode plate and the electrolyte satisfy the following relational expression: 1≦(δ×A ２ ) / (D×S)≦15.

2. 2. The lithium battery according to claim 1, wherein A and D satisfy the following relationship: 1.6≦(10 A) / D≦1.

9.

3. 2. The lithium battery of claim 1, wherein A is in the range of 6≦A≦15.

4. 2. The lithium battery of claim 1, wherein D is in the range of 40≦D≦90.

5. 5. The lithium battery according to claim 1, wherein S is in the range of 0.5≦S≦5.

6. 6. The lithium battery according to claim 1, wherein δ is in the range of 3≦δ≦5.

7. 7. The lithium battery according to claim 1, wherein the electrolyte solution comprises an organic solvent, a lithium salt, and an additive.

8. 8. The lithium battery of claim 7, wherein the organic solvent comprises at least one of a linear carbonate, a carboxylate, and a cyclic carbonate.

9. 8. The lithium battery of claim 7, wherein the lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, lithium difluoro(oxalato)borate, and lithium bis(oxalato)borate.

10. 8. The lithium battery of claim 7, wherein the additive comprises at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3,6-hexanetricarbonitrile, glyceryl trinitrate, 1,2-bis(cyanoethoxy)ethane, 1,4-dicyano-2-butene, fumaronitrile, succinonitrile, adipodinitrile, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

11. An electrical device (1) comprising a lithium battery (10) according to any one of claims 1 to 10.

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