CN1521882A - Lithium-ion secondary battery - Google Patents

Abstract

A lithium ion secondary battery includes a positive pole, a negative pole, an electrolyte and a diaphragm. The battery pole core is formed by stacking the positive and negative electrode sheets inserted into the bag-type diaphragm sleeve, and is clamped by the clamping device with the upper and lower ends of the open box structure to form the pole core body. The positive and negative current collectors are fastened with screws or riveted to form a current collecting structure, and are connected to the upper and lower cover plates of the battery through specific connecting parts. The pole core is closely matched with the battery shell and the battery cover to form a battery body with a strong pole core. The lithium-ion secondary battery has outstanding advantages such as high safety performance, excellent high-rate discharge characteristics, and simple production process, and is suitable for high-capacity, high-power applications such as electric vehicle power batteries.

Description

Lithium-ion secondary battery

【Technical field】

The invention relates to a secondary battery, in particular to a lithium-ion power battery with high safety performance, superior high-rate discharge characteristics and cycle characteristics.

【Background technique】

With the widespread use of various portable electronic products, lithium-ion secondary batteries are favored for their many superior properties such as high voltage, large specific energy, small self-discharge and no memory effect. In the civilian field, lithium-ion secondary batteries with a capacity of hundreds to thousands of mAh and low-to-medium power output have been successfully commercialized, and the world's total output has reached about 500 million per year. Recently, lithium-ion batteries with high capacity and high power output have also been studied, and their application directions are mainly electric vehicle power batteries, aerospace vehicle power supplies, and industrial and household energy storage systems. Lithium-ion batteries that meet these application requirements must have the following characteristics: (1) safe and reliable (2) high capacity (3) high-rate discharge characteristics and excellent cycle characteristics.

At present, lithium-ion secondary batteries generally adopt a winding structure. For small and medium capacity batteries, the manufacturing process is very simple. However, for high-capacity electric vehicle power batteries, if a winding structure is used, the pole pieces are more than ten meters or even tens of meters long, and the winding is extremely difficult. Moreover, the heat dissipation area of this structure is small, which is not conducive to the heat dissipation inside the battery, and affects the high rate discharge characteristics of the battery. Therefore, it is not suitable to use wound-type batteries in occasions that often need to be charged and discharged with a large current. A lithium-ion secondary battery is disclosed in CN2433736Y. The square battery pole pieces are arranged in layers separated by separators, and the two ends of the battery pole pieces are connected and fixed by stainless steel plates, copper plates or nickel plates. Although the battery with this structure improves the above-mentioned problems, it is more complicated and expensive in production to maintain the correct position of the pole piece and the diaphragm during the battery processing process and to place it with the correct procedure. Once the diaphragm is dislocated, it will cause a short circuit, which will definitely affect the safety performance of the battery. Moreover, the two ends of the battery pole core are connected and fixed, which greatly reduces the effective space inside the battery, which will inevitably affect the capacity of the battery. Simultaneously, this pole core fixing device is difficult to be fixed in the battery case, and it will bring great threat to the safety of the battery when it is used in the occasion with relatively large vibration like this. This is not allowed by high-capacity power batteries.

In addition, compared with other secondary batteries, lithium-ion batteries have higher internal resistance, so the voltage drops sharply when discharged at a high rate, the discharge time is greatly shortened, and the battery capacity is greatly reduced. The low conductivity of conventional electrodes is one of the main reasons for the high internal resistance of lithium-ion secondary batteries. At present, most commercial lithium-ion secondary batteries use single or multiple tabs as the current extraction method, but the current extraction and introduction are limited to a limited number of welding points, the conduction capacity is low, and the battery charge and discharge The current distribution in the process is not uniform enough. Therefore, power batteries with high capacity, high rate discharge characteristics and excellent cycle characteristics are not easy to use this current extraction method.

More importantly, in the design of large-capacity batteries, such as power batteries, their safety performance is the primary factor that must be considered. In common lithium-ion secondary batteries, the tabs used for current extraction are connected to the positive and negative cover plates by welding. When the battery is dropped and oscillated, the pole core is prone to movement, causing the positive and negative plates to deform, resulting in an internal short circuit of the battery. At the same time, the stress-bearing parts are concentrated on the welding points of the tabs, which can easily cause the welding points to fall off, thus causing a series of safety problems. Therefore, effective measures must be taken in the design to eliminate such hidden dangers.

【Content of invention】

The purpose of the present invention is to improve the prior art lithium-ion secondary battery internal resistance is relatively large, high-rate discharge performance and poor safety performance, thereby providing a high-safety performance, high-rate discharge characteristics and excellent cycle characteristics, production Lithium-ion power battery with outstanding advantages such as simple process.

The purpose of the present invention is achieved through the following technical solutions:

A lithium-ion secondary battery, mainly comprising: positive and negative electrode sheets, a diaphragm, an electrolyte and a battery case. The positive electrode sheet, the diaphragm and the negative electrode sheet are stacked and arranged to form a laminated pole core, which is fixed and stored in the battery case by a clamp. The clamping device is a box-type structure with upper and lower ends open, and clamps the pole core through single-side screw fastening.

The clamping tool is further improved to have protruding parts at both ends, and the sum of the protruding height and the height of the side wall of the clamping tool is equal to the height of the battery minus the thickness of the upper and lower cover plates.

The clamping device can also be further improved to be made of stainless steel plate, copper plate or aluminum plate, and the outer wall is indented.

The diaphragm is further improved into a single-side open pocket diaphragm case, and at least one of the stacked positive and negative pole pieces is inserted into the bag-type diaphragm case to form a stacked pole core.

The upper and lower ends of the lithium-ion secondary battery each include a current collector. The current collector includes a connecting block, a clip and a connecting piece. The clip clamps the positive and negative current collectors of the battery along the overlapping direction of the pole pieces. On the side wall of the connection block and through the connection piece, it is connected to the battery pole for conduction.

The positive and negative current collectors, connection blocks, clips, connection pieces and battery poles are connected as a whole by screw fastening or rivet riveting or screw fastening and welding or rivet riveting and welding.

The connecting sheet is further improved into a flexible connecting sheet formed by overlapping multiple layers of metal foils.

The positive pole of the lithium ion secondary battery of the present invention contains a layered composite oxide of lithium and transition metals, which are active materials with a specific structure and can react reversibly with lithium ions. Examples of such active material materials include: Li _x Ni _1-y Co _y O ₂ (wherein, 0.9 ≤ x ≤ 1.1, 0 ≤ y ≤ 1.0), Li _x Mn _2-y B _y O ₂ (wherein, B is transition metals, 0.9≤x≤1.1, 0≤y≤1.0). And the positive electrode also contains an electrode collector (usually aluminum foil) made of metal, a carbon-based material conductive agent, and a binder that bonds the positive electrode material to the electrode collector. Examples of the carbon-based material conductive agent include carbon black, carbon fiber and graphite, examples of the binder include fluorine-containing resins and polyolefin compounds such as PVDF, PTFE, VDF-HFP-TFE copolymer, and SBR.

The negative active material of the lithium ion secondary battery of the present invention is a carbon-based material capable of repeatedly intercalating and deintercalating lithium ions, and its examples include natural graphite, artificial graphite, mesocarbon microspheres (MCMB), and mesocarbon fibers (MCF). . And the negative electrode also contains a metal electrode collector (usually copper foil) and a binder that binds the negative electrode material to the electrode collector. Examples of the binder include fluorine-containing resins and polyolefin compounds such as PVDF, PTFE , VDF-HFP-TFE copolymer and SBR.

The electrolyte solution of the lithium ion secondary battery of the present invention is a mixed solution containing lithium salt chain acid ester and cyclic acid acid ester. Examples of lithium salts include lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium chloroaluminate, lithium halides, lithium fluorocarbonyl oxyphosphate and lithium fluorocarbonyl sulfonate, among which one or a mixture thereof. Examples of chain esters include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl propyl carbonate (EPC), diphenyl carbonate (DPC), methyl acetate (MA), ethyl acetate (EA), ethyl propionate (PA), dimethoxyethane, diethoxyethane and other chain organic esters containing fluorine, sulfur or unsaturated bonds , one or a mixture of them can be used. Examples of cyclic acid esters include ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), sultone, and other fluorine- and sulfur-containing Or unsaturated bond-containing cyclic organic esters, one of them or a mixture thereof can be used.

The lithium ion secondary battery of the invention has the advantages of low internal resistance, excellent high rate discharge performance, no obvious temperature rise during high current discharge, and good safety performance. The battery made of this structure is suitable for high-capacity and high-power output applications, especially for automotive power batteries.

The present invention will be further described below with reference to the accompanying drawings and embodiments.

【Description of drawings】

FIG. 1 is a schematic structural view of the lithium ion secondary battery of the present invention.

Fig. 2 is a schematic diagram of the battery pole piece of the lithium ion secondary battery of the present invention.

FIG. 3 is a structural diagram of a clamping tool for a lithium-ion secondary battery of the present invention.

Fig. 4 is a schematic diagram of cooperation between the pole core body, the battery case and the battery cover plate of the lithium ion secondary battery of the present invention.

Labels are explained as follows:

1 Laminated battery pole core 2 Clamping device

3 Battery case 4,4’ Connecting pieces

5, 5’ Connection Block 6, 6’ Clip

7, 7’ Spacer 8, 8’ Battery cover

9 bag diaphragm sleeve 10 pole piece

11 Electrode current collector 12 Protruding part

13, 13' Pole

【Detailed ways】

Please refer to Fig. 1, the lithium-ion secondary battery of the present invention includes a laminated battery pole core 1, a clamping tool 2, a battery case 3, a connecting piece 4, 4' at the upper and lower ends, and a connecting piece 5 each. , 5', each of a clip 6,6', each of a spacer 7,7', each of a battery cover 8,8', each of a pole 13,13'.

Please refer to FIG. 2 , the lithium-ion secondary battery of the present invention forms a laminated battery pole core 1 through a bag-type diaphragm case 9 , that is, at least one of the positive and negative electrode sheets 10 is inserted into the bag-type diaphragm case 9 and stacked. In this way, the original very long pole piece can be divided into several small pieces, thereby greatly reducing the difficulty of battery assembly. The bag-type diaphragm sleeve 9 is formed by high-temperature welding of the periphery of the diaphragm to form a single-side open bag structure. The pole piece 10 is inserted from the opening edge, the electrode collector 11 is exposed outside, and the other periphery of the bag-type diaphragm sleeve 9 is welded firmly, completely isolating the positive and negative pole pieces 10 of the battery. Therefore, the advantages of the bag-type diaphragm sleeve 9 are: (1) the production process is simple and easy; (2) it can effectively prevent the internal short circuit of the battery and improve the safety performance. In addition, the square stacked structure increases the heat dissipation area, which is conducive to improving the high rate discharge characteristics of the battery.

Please refer to Figure 3, the clamping device 2 is a box-type structure with upper and lower ends open, and is used to clamp the above-mentioned laminated pole core 1. The clamping device 2 is made of stainless steel plate, copper plate or aluminum plate, and the outer wall is marked with Indentation, the pole core is clamped by one-sided screw fastening. This can not only effectively prevent the movement of the pole core, avoid the deformation of the positive and negative pole pieces during the battery drop and vibration process and cause the internal short circuit of the battery, but also the box-type unilateral fastening method effectively saves the internal effective space of the battery , to provide convenience for the large capacity of the battery. At the same time, there are protruding parts 12 on both sides of the clamping device. During battery assembly (please refer to Figure 4), when the upper and lower battery cover plates 8, 8' are welded to the battery case 3, the protruding parts 12 at both ends are pushed against The two sides of the battery cover plate 8, 8' prevent the entire pole core body from moving up and down, and at the same time, the outer wall of the clamping device is closely matched with the inner wall of the battery case to form a battery body with a firm pole core.

The connecting sheets 4, 4' are flexible connecting sheets made of overlapping layers of metal foils, which are superior to other commonly used methods in terms of electrical conductivity and flexibility. When a battery with such a structure is used in an environment with large vibrations, the force on each part of the battery current collection structure is further dispersed. There is almost no force at the connection point of the connecting sheet, and it is not easy to fall off, which greatly improves the safety performance of the battery.

In the present invention, the positive and negative electrode current collectors at both ends of the lithium-ion secondary battery are respectively clamped on the side walls of the connecting blocks 5, 5' along the overlapping direction of the pole pieces by clips 6, 6', and welded Fastened with screws or welded with rivets and riveted together to form a current collecting structure. The connection blocks 5 and 5' are T-shaped structures made of aluminum or copper. The force-bearing surface of this connection block determines that it will not be affected by the strength of the positive and negative current collectors, and the process is simple, which fully guarantees the charging and discharging process. The uniform distribution of medium current effectively eliminates the influence of contact resistance and greatly reduces the internal resistance of the battery.

The preparation process of the positive plate of the lithium ion secondary battery of the present invention: PVDF is dissolved in NMP, LiCoO ₂ and acetylene black are added in this solution, fully mix and make slurry, and its composition is LiCoO ₂ : acetylene black : PVDF =92:4:4. This slurry was evenly coated on both sides of a 20 μm aluminum foil, and dried at 120° C. for 3 hours. After rolling, a positive electrode sheet with a size of 220×120 mm ² and a thickness of 160 μm was obtained. Then scrape off the dressing layer on the edge of the positive electrode sheet to expose an aluminum foil with a width of 20 mm.

The preparation process of the negative plate of the lithium-ion secondary battery of the present invention: dissolve PVDF in NMP, add artificial graphite into the solution, fully mix to make slurry, and its composition is artificial graphite:PVDF=95:5. The slurry was evenly coated on both sides of a 20 μm copper foil, and dried at 120° C. for 3 hours. After calendering, a negative electrode sheet with a size of 220×120 mm2 and a thickness of 160 μm was obtained. The coating layer on the edge of the negative electrode sheet was scraped off again to expose a copper foil with a width of 20 mm.

The assembly method of the lithium-ion secondary battery of the present invention is to pack the above-mentioned positive and negative electrodes into bag-type separator bags made of microporous polypropylene material with a thickness of 40 μm respectively, stack them neatly and clamp them with clamping device 2. Into the battery pole core body. At this time, the positive and negative electrode collectors of aluminum foil and copper foil are respectively exposed at both ends of the pole core body, and the positive and negative electrode collectors of the battery are respectively fastened to the upper and lower connecting blocks with screws and clips along the overlapping direction of the pole pieces to form Positive and negative polarity collector structure. Put the battery pole core into the battery shell, assemble the battery connecting piece 4, 4', the spacer 7, 7', the cover plate 8, 8' and other accessories at both ends, and then weld the battery cover plate to the battery shell port. The outer wall of the pole core is closely matched with the inner wall of the battery case, and the protruding parts at both ends of the clamping device on the pole core body are supported on both sides of the battery cover plate. After the battery is assembled, the electrolyte solution formed by dissolving LiPF ₆ in a mixed solvent of EC/DEC=1:1 at a concentration of 1mol/dm3 is injected into the battery case and sealed to make a 100Ah square stacked lithium-ion power pack. Battery.

Battery Characteristic Test

【Discharge performance】

Charge the square lithium-ion power battery made by the above method to 4.1V with a constant current of 20A, charge with a constant voltage after the voltage rises to 4.1V, and the cut-off current is 0.5A; then discharge with a constant current of 20A, and the cut-off voltage 3.0V. Measure initial capacity and battery internal resistance.

【Load characteristics】

Charge the square lithium-ion secondary battery made by the above method to 4.1V with a constant current of 20A, charge with a constant voltage after the voltage rises to 4.1V, and cut off the current at 0.5A; then discharge with a constant current of 100A, until Voltage 3.0V. The capacity retention rate under high load conditions and the magnitude of temperature rise during discharge were measured.

【Safety Features】

Drop test: Charge the square lithium-ion power battery made by the above method to 4.1V at a constant current of 20A, charge at a constant voltage after the voltage rises to 4.1V, and cut off the current at 0.5A; measure the internal resistance of the battery before dropping and voltage; then the battery is dropped horizontally from a drop platform with a height of 1m to the concrete floor on one side, and each six sides are horizontally free-falled once for 1 cycle, and the battery is measured after each drop cycle At the same time, carefully observe whether the battery has leakage, heat, smoke and explosion during the drop process; a total of 3 cycles have been dropped.

The results of the above tests are shown in the table below.

Li-ion secondary battery performance test results structure type Initial discharge capacity (Ah) Battery internal resistance (mΩ) 100A/20A discharge capacity maintenance rate (%) Temperature rise at 100A discharge (°C) Whether the internal resistance and voltage of the battery change before and after the drop Whether the battery leaks, heats up, smokes, explodes before and after the drop Example square stack 102 2.3 93.2 1.5 none none

Claims (10)

1. A lithium-ion secondary battery, mainly comprising: positive and negative electrode sheets, a diaphragm, an electrolyte and a battery case, and the stacked pole core is formed by stacking the positive electrode sheet, the diaphragm and the negative electrode sheet, and is fixed and stored in the battery by a clamp The shell is characterized in that: the clamping device is a box-type structure with upper and lower ends open, and the pole core is clamped by a single side screw fastening method. 2. The lithium-ion secondary battery as claimed in claim 1, wherein both ends of the clamping tool have protruding parts, and the sum of the protruding height and the height of the side wall of the clamping tool is equal to the height of the battery minus its upper and lower parts. Cover thickness. 3. The lithium-ion secondary battery according to claim 1 or 2, wherein the clamping device is made of stainless steel plate, copper plate or aluminum plate, and the outer wall is indented. 4. The lithium-ion secondary battery as claimed in claim 1, characterized in that: the separator is a unilaterally opened pocket-type separator sleeve, and at least one of the positive and negative pole pieces arranged in layers is inserted into the pole piece. The bag-type diaphragm sleeve forms a laminated pole core. 5. The lithium-ion secondary battery as claimed in claim 1, characterized in that: each of the two ends of the lithium-ion secondary battery includes a current collecting part, and the current collecting part includes a connecting block, a clip and a connecting piece, and the clip The sheet clamps the positive and negative electrode collectors of the battery on the side wall of the connection block along the overlapping direction of the pole pieces, and is connected to the battery pole through the connection sheet. 6. The lithium-ion secondary battery according to claim 5, characterized in that: the positive and negative electrode current collectors, connection blocks, clips, connection pieces and battery poles are fastened by screws or rivets It is connected as a whole by means of fastening or screw fastening and welding or rivet riveting and welding. 7. The lithium ion secondary battery according to claim 5, characterized in that the connecting sheet is a flexible connecting sheet formed by overlapping multiple layers of metal foil. 8. The lithium ion secondary battery according to claim 1, characterized in that: the positive electrode active material is selected from the general formula: Li _x Ni _1-y Co _y O ₂ (wherein, 0.9≤x≤1.1, 0 ≤y≤1.0), Li _x Mn _2- yB _{yO 2} (wherein, B is a transition metal, 0.9≤x≤1.1, 0≤y≤1.0) lithium and transition metal layered composite oxide. 9. The lithium ion secondary battery according to claim 1, characterized in that: the negative electrode active material is selected from natural graphite, artificial graphite, mesocarbon microspheres, and mesocarbon fibers, which are capable of repeatedly intercalating lithium ions and deintercalated graphitized carbon-based materials. 10. The lithium ion secondary battery according to claim 1, characterized in that: the electrolyte is a mixed solution of chain esters and cyclic esters containing lithium salts, wherein the lithium salts include lithium perchlorate, Lithium hexafluorophosphate, lithium tetrafluoroborate, lithium chloroaluminate, lithium halide, lithium fluorocarbonyl oxyphosphate and lithium fluorocarbon sulfonate or their mixture; chain esters include dimethyl carbonate, diethyl carbonate, methyl carbonate Ethyl, ethyl propyl carbonate, diphenyl carbonate, methyl acetate, ethyl acetate, ethyl propionate, dimethoxyethane, diethoxyethane and other fluorine-containing, sulfur-containing or unsaturated One or a mixture of chain organic esters with bonds; cyclic esters include ethylene carbonate, propylene carbonate, vinylene carbonate, γ-butyrolactone, sultone and other fluorine-containing, sulfur-containing or One or a mixture of cyclic organic esters of unsaturated bonds.

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