Method for producing negative electrode carbon material

Abstract

A method for manufacturing a negative electrode carbon material, suitable for a lithium ion secondary battery, comprising: (A) heating a heavy oil to become a green coke; (B) heating the green coke to 850-900°C at a first heating rate of 3-5°C / min for at least 4 hours to become a carbon-containing material; (C) grinding the carbon-containing material and classifying the ground carbon-containing material to obtain a carbon-containing powder having a D50 of 8-12 μm and a D10 of 1-8 μm; (D) heating the carbon-containing powder to 1030-1220°C at a second heating rate of 3-10°C / min for at least 4 hours to become a carbon material powder; and (E) heating the carbon material powder to which a predetermined amount of pitch is added to 1030-1220°C at a third heating rate of 0.90-1.25°C / min for at least 5 hours to become a pitch-modified soft carbon. By adjusting the D50 and D10 particle size distribution of the carbon-containing powder through the grinding classification of step (C) and the third heating rate and heating temperature range of step (E), the properties of the soft carbon produced in step (E) can be changed to thereby improve the fast charge and discharge capability of the lithium ion secondary battery after assembly.

Description

Technical Field

[0001] This invention relates to a method for manufacturing carbon materials, and more particularly to a method for manufacturing a negative electrode carbon material. Background Technology

[0002] Among the many types of rechargeable batteries supplied to the general consumer, lithium-ion batteries are currently the most widely used and popular choice. As is well known, common lithium-ion batteries use lithium cobalt oxide, lithium iron phosphate, or lithium manganese oxide as the positive electrode, while the negative electrode material is carbon.

[0003] Furthermore, technicians in the oil refining industry know that the refining process often produces large quantities of heavy hydrocarbon oil. For refineries, this heavy hydrocarbon oil is generally sold as low-priced fuel oil, generating little economic value. However, it should be noted that because the main component of heavy hydrocarbon oil is hydrocarbons, it can be processed through multiple steps to produce carbon anode materials used in lithium-ion secondary batteries.

[0004] For example, the applicant previously disclosed precursor components and amorphous carbon materials in Taiwan Invention Patent Certificate No. TWI603528 (hereinafter referred to as Case 1), and also disclosed soft carbon and its preparation method in Taiwan Invention Patent Certificate No. TWI720805 (hereinafter referred to as Case 2). In the disclosed technologies of Case 1 and Case 2, numerous analyses were made regarding the application of amorphous carbon materials and soft carbon in the charge-discharge capabilities of lithium-ion secondary batteries. However, for researchers and developers of negative electrode materials for lithium-ion secondary batteries, improving the battery's capacity retention during fast charging and discharging, as well as its cycle life, has always been a major issue requiring breakthroughs in the industry.

[0005] As explained above, improving the manufacturing process of negative electrode carbon materials to enhance the rapid charge / discharge capability and cycle life of lithium-ion secondary batteries is a challenge that those skilled in the art need to overcome. Summary of the Invention

[0006] The purpose of this invention is to provide a method for manufacturing a negative electrode carbon material that can improve the fast charging and discharging capability and cycle life of a battery.

[0007] The method for preparing the negative electrode carbon material of the present invention is applicable to lithium-ion secondary batteries and includes the following steps in sequence: step (A), step (B), step (C), step (D), and step (E).

[0008] Step (A) involves heating a batch of heavy oil to turn it into a batch of green coke.

[0009] Step (B) involves heating the batch of raw coke to 850°C to 900°C at a first heating rate of 3°C to 5°C to 5°C and holding it at that temperature for at least 4 hours to transform it into a batch of carbon-containing material.

[0010] Step (C) involves grinding the batch of carbon-containing material and separating a batch of carbon-containing powder with a D50 between 8 μm and 12 μm and a D10 between 1 μm and 8 μm from the ground carbon-containing material.

[0011] Step (D) involves heating the batch of carbon-containing powder to 1030°C to 1220°C at a second heating rate of 3°C to 10°C to 10°C to hold at that temperature for at least 4 hours, thereby making it a batch of carbon material powder.

[0012] Step (E) involves adding a predetermined amount of asphalt to the batch of carbon powder, then heating the batch of carbon powder with added asphalt to 1030°C to 1220°C at a third heating rate of 0.90°C / min to 1.25°C / min and holding it at that temperature for at least 5 hours, so that it becomes a batch of asphalt-modified soft carbon.

[0013] In the method for preparing the negative electrode carbon material of the present invention, in step (C), carbon powder with D50 between 10 μm and 12 μm and D10 between 6 μm and 8 μm is graded from the ground carbon-containing material; in step (D), the batch of carbon powder is heated to 1080°C to 1120°C; in step (E), the predetermined amount is at least 4 parts by weight based on 100 parts by weight of the total weight of the batch of carbon powder, and the batch of carbon powder with added asphalt is heated to 1080°C to 1120°C at a third heating rate of 1.20°C / min to 1.25°C / min, so that the batch of asphalt-modified soft carbon becomes a batch of general soft carbon.

[0014] In the method for preparing the negative electrode carbon material of the present invention, in step (C), carbon powder with D50 between 8 μm and 10 μm and D10 between 2 μm and 6 μm is graded from the ground carbon-containing material; in step (D), the batch of carbon powder is heated to 1080°C to 1120°C; in step (E), based on a total weight of 100 parts by weight of the carbon powder, the predetermined amount is at least 4 parts by weight, and the batch of carbon powder with added asphalt is heated to 1080°C to 1120°C at a third heating rate of 1.20°C / min to 1.25°C / min, so that the batch of asphalt-modified soft carbon becomes a batch of fast-charging soft carbon.

[0015] In the method for preparing the negative electrode carbon material of the present invention, in step (C), carbon powder with D50 between 10 μm and 12 μm and D10 between 6 μm and 8 μm is graded from the ground carbon-containing material; in step (D), the batch of carbon powder is heated to 1180°C to 1220°C; in step (E), based on a total weight of 100 parts by weight of the carbon powder, the predetermined amount is at least 4 parts by weight, and the batch of carbon powder with added asphalt is heated to 1180°C to 1220°C at a third heating rate of 0.92°C / min to 0.98°C / min, so that the batch of asphalt-modified soft carbon becomes a batch of high-temperature life-life soft carbon.

[0016] In the method for preparing the negative electrode carbon material of the present invention, in step (C), carbon powder with D50 between 10 μm and 12 μm and D10 between 6 μm and 8 μm is graded from the ground carbon-containing material; in step (D), the batch of carbon powder is heated to 1030°C to 1070°C; in step (E), based on a total weight of 100 parts by weight of the carbon powder, the predetermined amount is at least 4 parts by weight, and the batch of carbon powder with added asphalt is heated to 1030°C to 1070°C at a third heating rate of 1.12°C / min to 1.18°C / min, so that the batch of asphalt-modified soft carbon becomes a batch of high-capacity soft carbon.

[0017] The beneficial effects of the present invention are as follows: by grinding and classifying in step (C) to adjust the particle size distribution of D50 and D10 of the carbon-containing powder, and in conjunction with the third heating rate between 0.90°C / min and 1.25°C / min and the heating temperature range of 1030°C to 1220°C in step (E), the characteristics of the batch of asphalt-modified soft carbon obtained in step (E) can be changed, thereby improving the fast charge and discharge capability and cycle life of the batch of asphalt-modified soft carbon after being assembled into a lithium-ion secondary battery. Attached Figure Description

[0018] Other features and effects of the present invention will be clearly presented in the embodiments with reference to the accompanying drawings, wherein:

[0019] Figure 1 This is a partial cross-sectional view illustrating a first embodiment of the lithium-ion secondary battery of the present invention;

[0020] Figure 2 This is a partial cross-sectional view illustrating a second, a third, and a fourth embodiment of the lithium-ion secondary battery of the present invention;

[0021] Figure 3 It is a voltage-to-capacity curve, illustrating the charge-discharge curves of the general type half-cell of the first embodiment of the present invention and the fast-charging type half-cell of the second embodiment.

[0022] Figure 4 It is a graph showing the relationship between capacity retention rate and charge rate (charge C rate), illustrating the charging capabilities of the general full battery (8Ah) of the first embodiment of the present invention and the fast-charging full battery (8Ah) of the second embodiment of the present invention;

[0023] Figure 5 It is a graph showing the relationship between capacity retention rate and discharge rate (C rate), illustrating the discharge capacity of the general full battery (8Ah) of the first embodiment of the present invention and the fast-charging full battery (8Ah) of the second embodiment of the present invention;

[0024] Figure 6 It is a voltage-to-capacity curve, illustrating the charge-discharge curves of the general type half-cell of the first embodiment of the present invention and the high-temperature life type half-cell of the third embodiment.

[0025] Figure 7 It is a graph showing the relationship between capacity retention rate and charge / discharge cycles, illustrating the fast charge / discharge (2C) cycle life test of the general full battery (8Ah) of the first embodiment of the present invention and the high temperature life full battery (8Ah) of the third embodiment at room temperature (25°C);

[0026] Figure 8 It is a graph showing the relationship between capacity retention rate and charge / discharge cycles, illustrating the fast charge / discharge (2C) cycle life test of the general full battery (8Ah) of the first embodiment of the present invention and the high temperature life full battery (8Ah) of the third embodiment at high temperature (45°C);

[0027] Figure 9 It is a voltage-to-capacity curve diagram, illustrating the charge-discharge curves of the general type half-cell of the first embodiment of the present invention and the high-capacity type half-cell of the fourth embodiment.

[0028] Figure 10 This is a graph showing the relationship between capacity retention and charge / discharge cycles, illustrating the fast charge / discharge (2C) cycle life test of the general full battery (8Ah) of the first embodiment and the high-capacity full battery (8Ah) of the fourth embodiment at room temperature (25°C); and

[0029] Figure 11 This is a graph showing the relationship between capacity retention and charge / discharge cycles, illustrating the fast charge / discharge (2C) cycle life test of the general full battery (8Ah) of the first embodiment and the high-capacity full battery (8Ah) of the fourth embodiment at high temperature (45°C). Detailed Implementation

[0030] See Figure 3A first embodiment of the method for preparing the negative electrode carbon material of the present invention is a negative electrode carbon material suitable for lithium-ion secondary batteries and includes the following steps in sequence: step (A), step (B), step (C), step (D), and step (E).

[0031] Step (A) is the coke formation step. Specifically, it involves heating a batch of heavy oil to form a batch of coke. More specifically, step (A) involves first transferring the batch of heavy oil to a reaction vessel (not shown) and heating it for 1 to 16 hours at a coking temperature of 480°C to 550°C and a pressure range of 0.2 MPa to 4 MPa, causing the batch of heavy oil in the reaction vessel to undergo cracking and condensation polymerization to generate the batch of coke. In step (A) of the first embodiment of the present invention, the batch of heavy oil is heated for 4 hours at a coking temperature of 500°C and a pressure of 1.0 MPa.

[0032] Step (B) is a pre-calcination carbonization step. Specifically, step (B) involves heating the batch of green coke to 850°C to 900°C at a first heating rate of 3°C / min to 5°C / min and holding it at that temperature for at least 4 hours, thereby transforming it into a batch of carbon-containing material. The purpose of this pre-calcination carbonization step is to allow the batch of green coke to undergo at least one of a polycondensation reaction, a dehydrogenation reaction, and a cracking reaction, causing the batch of green coke to begin to tend towards having sp... 2 Hybrid orbital domain (sp 2 The batch of carbon-containing materials (hybridized). In step (B) of the first embodiment of the present invention, the batch of coke is heated to 900°C at a first heating rate of 5°C / min for 4 hours.

[0033] Step (C) is a grinding and grading step. Specifically, step (C) involves grinding the batch of carbon-containing material and grading a batch of carbon-containing powder with a D50 between 8 μm and 12 μm and a D10 between 1 μm and 8 μm from the ground carbon-containing material. In step (C) of this first embodiment of the present invention, a cyclone classifier is used to sieve the ground carbon-containing material to grade carbon-containing powder with a D50 between 10 μm and 12 μm, a D10 between 6 μm and 8 μm, and a D90 between 18 μm and 20 μm.

[0034] Step (D) is a high-temperature carbonization step. Specifically, step (D) involves heating the batch of carbon-containing powder to 1030°C to 1220°C at a second heating rate of 3°C / min to 10°C / min and holding it at that temperature for at least 4 hours, thereby forming a batch of carbon material powder. The purpose of this high-temperature carbonization step of the present invention is to enable the residual coke in the batch of carbon-containing powder to undergo at least one of a condensation reaction, a cracking reaction, and a dehydrogenation reaction, so that the carbon in the residual coke rearranges into sp... 2 The mixture is then mixed to form the batch of carbon powder. Preferably, in step (D), the batch of carbon powder is heated to 1080°C to 1120°C. In step (D) of the first embodiment of the present invention, the batch of carbon powder is heated to 1100°C at a second heating rate of 10°C / min.

[0035] Step (E) is a modification carbonization step. Specifically, step (E) involves adding a predetermined amount of asphalt to the batch of carbon powder, then heating the batch of carbon powder with added asphalt to 1030°C to 1220°C at a third heating rate of 0.90°C / min to 1.25°C / min and holding it at that temperature for at least 5 hours, thus creating a batch of asphalt-modified soft carbon. Given that the carbon powder obtained in step (C) of this first embodiment of the invention has surface damage and micropores, resulting in an increase in the specific surface area of ​​the batch of carbon powder after the high-temperature carbonization step, the aforementioned result makes the batch of carbon powder easily wetted by the electrolyte when subsequently used as the negative electrode of a lithium-ion secondary battery, thereby affecting the battery performance. Therefore, the purpose of the modified carbonization step of the present invention is to utilize the softening point of asphalt so that the batch of carbon powder with added asphalt can reduce the viscosity of the asphalt during the heating process of step (E) when the temperature reaches the softening point of the asphalt. The asphalt with reduced viscosity can modify the tiny pores on the surface of the batch of carbon powder, thereby obtaining soft carbon modified with asphalt and with reduced specific surface area.

[0036] Preferably, in step (E), the predetermined amount is at least 4 parts by weight, based on a total weight of 100 parts by weight of the carbon powder, and the batch of carbon powder with added asphalt is heated to 1080°C to 1120°C at a third heating rate of 1.20°C / min to 1.25°C / min. In step (E) of the first embodiment of the present invention, the batch of carbon powder with added asphalt is heated to 1100°C at a third heating rate of 1.22°C / min, causing the batch of asphalt-modified soft carbon to become a batch of general soft carbon.

[0037] A second embodiment of the method for preparing the negative electrode carbon material of the present invention is substantially the same as the first embodiment, except that step (C) is different. Preferably, the D10 fraction in step (C) is between 2 μm and 6 μm. In step (C) of the second embodiment of the method for preparing the negative electrode carbon material of the present invention, carbon powder with D50 between 8 μm and 10 μm, D10 between 3 μm and 5 μm, and D90 between 16 μm and 18 μm is graded from the ground carbon-containing material, so that after step (E) is performed, the batch of pitch-modified soft carbon in the second embodiment becomes a batch of fast-charging soft carbon.

[0038] A third embodiment of the method for preparing the negative electrode carbon material of the present invention is substantially the same as the first embodiment, except that in step (D), the batch of carbon powder is heated to 1180°C to 1220°C; and in step (E), the batch of carbon powder with added asphalt is heated to 1180°C to 1220°C at a third heating rate of 0.92°C / min to 0.98°C / min, thereby making the batch of asphalt-modified soft carbon a batch of high-temperature lifespan soft carbon. In this third embodiment of the present invention, step (D) involves heating the batch of carbon powder to 1200°C, and step (E) involves heating the batch of carbon powder with added asphalt to 1200°C at a third heating rate of 0.95°C / min.

[0039] A fourth embodiment of the method for preparing the negative electrode carbon material of the present invention is substantially the same as the first embodiment, except that in step (D), the batch of carbon-containing powder is heated to 1030°C to 1070°C; and in step (E), the batch of carbon material powder with added asphalt is heated to 1030°C to 1070°C at a third heating rate of 1.12°C / min to 1.18°C / min, thereby making the batch of asphalt-modified soft carbon a batch of high-capacity soft carbon. In this fourth embodiment of the present invention, step (D) involves heating the batch of carbon-containing powder to 1050°C, and step (E) involves heating the batch of carbon material powder with added asphalt to 1050°C at a third heating rate of 1.16°C / min.

[0040] The process parameters for each embodiment of the method for manufacturing the negative electrode carbon material of the present invention are summarized in Table 1 below.

[0041] Table 1.

[0042]

[0043] See Figure 1A first embodiment of the lithium-ion secondary battery of the present invention includes a first casing 20, a negative electrode 21 disposed within the first casing 20 and containing a negative electrode carbon material (i.e., general soft carbon) prepared by the method of the first embodiment, a positive electrode 22 disposed within the first casing 20 and spaced apart from the negative electrode 21, an electrolyte 23 filled within the first casing 20, and a separator 24 disposed within the first casing 20 and between the positive electrode 22 and the negative electrode 21, thereby making the lithium-ion secondary battery of the first embodiment a general lithium-ion secondary battery 2. Further, the first casing 20 is composed of a negative electrode shell portion 201 located on the upper side and a positive electrode shell portion 202 located on the lower side, and the space within the first casing 20 is sealed between the negative electrode shell portion 201 and the positive electrode shell portion 202 by a sealing ring 25. The detailed manufacturing method of the negative electrode 21 of the general lithium-ion secondary battery 2 of the first embodiment of the present invention is described below.

[0044] First, the batch of general-type soft carbon was crushed using a crusher (not shown in the figure), and then sieved through a sieve (mesh size 38μm) to obtain a soft carbon anode material. Next, 9.1g of this soft carbon anode material, 0.5g of polyvinylidene fluoride (PVDF, manufactured by Kureha Chemical Industry Co., Ltd., trade name KF9200), and 0.4g of conductive carbon black (purchased from Timcal, trade name Super) were uniformly mixed. P), and 12g to 15g of N-methyl-2-porrolidone (NMP) are mixed to form a solution. The solution is then coated onto a copper foil with a thickness of 14μm and dried at 85°C for 0.5 hours to remove NMP and moisture, thereby forming the negative electrode 21 of the general lithium-ion secondary battery 2. The negative electrode 21 includes the copper foil and a conductive film formed on the copper foil with a thickness of 20μm to 22μm. The conductive film contains 91wt% of the soft carbon negative electrode material, 5wt% of polyvinylidene fluoride, and 4wt% of conductive carbon black, based on a total weight of 100wt%.

[0045] Assembly of a standard CR2032 half-cell (button cell)

[0046] The assembly of the general CR2032 half-cell of the first embodiment of the present invention involves assembling the aforementioned negative electrode, a lithium metal sheet serving as the positive electrode, an electrolyte, and a separator [manufacturer: Celgard, material: polypropylene (PP) and polyethylene (PE)] into a CR2032 button-type half-cell; wherein, based on a total weight of 100wt% of the electrolyte, the electrolyte contains 99wt% of a 1M LiPF6 solution and 1wt% of vinylene carbonate. The LiPF6 solution contains LiPF6, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), and the volume ratio of EC:EMC:DMC is 1:1:1.

[0047] Assembly of a standard 18650 full battery

[0048] The assembly of the general 18650 full cell in the first embodiment of this invention is carried out using a winding machine (not shown) to assemble a negative electrode, a positive electrode, an electrolyte, and a separator (brand: Celgard, material: PP and PE) into an 18650 full cell. Specifically, the positive electrode includes an aluminum foil as a conductive carrier and a conductive film formed on the surface of the aluminum foil. Based on a total weight of 100 wt%, the conductive film includes 91 wt% of the positive electrode components [containing lithium manganese oxide (LiMn2O4; abbreviated as LMn) and lithium nickel cobalt manganese oxide (LiNi).] 1 / 3 Mn 1 / 3 Co 1 / 3 The electrolyte contains 5 wt% of a binder (PVDF) and 4 wt% of a conductive agent (conductive carbon black, manufacturer: Timcal, trade name: Super P), with a total weight ratio of 30:70 for lithium manganese oxide and lithium nickel cobalt manganese oxide. The electrolyte comprises 99 wt% of a 1M LiPF6 solution and 1 wt% of vinylene carbonate. The LiPF6 solution contains LiPF6, EC, EMC, and DMC, with a volume ratio of EC:EMC:DMC of 1:1:1.

[0049] See Figure 2A second embodiment of the lithium-ion secondary battery 3 of the present invention includes a second outer casing 30, a negative electrode 31 disposed within the second outer casing 30 and containing a negative electrode carbon material prepared by any one of the methods of the second, third, and fourth embodiments, a positive electrode 32 disposed within the second outer casing 30 and spaced apart from the negative electrode 31, an electrolyte 33 filled within the second outer casing 30, and a separator 34 disposed within the second outer casing 30 and positioned between the positive electrode 32 and the negative electrode 31. The second outer casing 30 of the second embodiment is the same as the first outer casing 20 of the first embodiment, and is also composed of a negative electrode shell portion 301 located on the upper side and a positive electrode shell portion 302 located on the lower side. The space inside the second outer casing 30 is sealed between the negative electrode shell portion 301 and the positive electrode shell portion 302 by a sealing ring 35. In a second embodiment of the lithium-ion secondary battery of the present invention, the negative electrode 31 contains the negative electrode carbon material (i.e., fast-charging soft carbon) obtained by the manufacturing method of the second embodiment, thereby making the lithium-ion secondary battery 3 a fast-charging lithium-ion secondary battery.

[0050] Assembly of Fast-Charging CR2032 Half-Battery (Button Cell)

[0051] The assembly of the fast-charging CR2032 half-cell of the second embodiment of the present invention is generally the same as that of the general CR2032 half-cell of the first embodiment. The difference is that the soft carbon negative electrode material in the conductive film of the negative electrode is replaced by the fast-charging soft carbon obtained by the method of the second embodiment.

[0052] Assembly of the fast-charging 7799130 full battery>

[0053] The assembly of the fast-charging 7799130 full battery in the second embodiment of this invention utilizes the stacking machine to assemble a negative electrode, a positive electrode, an electrolyte, and a separator (manufacturer: Celgard, material: PP, thickness: 20μm) into a 7799130 full battery. Specifically, the batch of fast-charging soft carbon is crushed using the crusher, and then sieved through the screen to obtain a soft carbon negative electrode material. Next, 467.5g of the soft carbon anode material, 45g of PVDF (manufactured by Kureha Chemical Industry Co., Ltd., trade name KF9200), 20g of conductive agent (conductive carbon black, manufacturer: Timcal, trade name: Super P), 467.5g of mesophase graphite powder (purchased from China Steel Carbon Chemical Co., Ltd., trade name MGP), and 1233g to 1438g of NMP were uniformly mixed to form a mixture. The mixture was then coated onto a copper foil with a thickness of 14μm and dried at 85°C for 0.5 hours to remove NMP and moisture, thus forming the anode of the fast-charging 7799130 full battery. The anode includes the copper foil and a conductive film with a thickness of 100μm to 110μm formed on the copper foil. Based on a total weight of 100wt% for the conductive film of the negative electrode of the fast-charging 7799130 full battery, the conductive film comprises 93.5wt% of the negative electrode component [based on a total weight of 100wt% for the negative electrode component, which contains 50wt% of the soft carbon negative electrode material and 50wt% of MGP], 4.5wt% of the binder (type: PVDF), and 2wt% of the conductive carbon black. The positive electrode of the fast-charging 7799130 full battery comprises an aluminum foil serving as a conductive carrier, and a conductive film formed on the surface of the aluminum foil. Based on a total weight of 100wt% for the conductive film of the positive electrode of the fast-charging 7799130 full battery, the conductive film comprises 92.5wt% of lithium nickel cobalt manganese oxide (LNMC), 2.5wt% of the binder (type: PVDF), and 5wt% of the conductive aid (type: conductive carbon black, manufacturer: Timcal, trade name: Super P). Based on a total weight of 100 wt%, the electrolyte contains 99 wt% of a 1M LiPF6 solution and 1 wt% of vinylene carbonate. The LiPF6 solution contains LiPF6, EC, EMC, and diethylcarbonate (DEC), with a volume ratio of EC:EMC:DEC of 1:1:1.

[0054] See also Figure 2A third embodiment of the lithium-ion secondary battery 3 of the present invention is generally the same as the second embodiment, except that in the third embodiment of the lithium-ion secondary battery 3 of the present invention, the negative electrode 31 contains the negative electrode carbon material (i.e., high-temperature life soft carbon) obtained by the manufacturing method of the third embodiment, thereby making the lithium-ion secondary battery 3 a high-temperature life lithium-ion secondary battery.

[0055] Assembly of High-Temperature Life CR2032 Half-Cell (Button Cell)

[0056] The assembly of the high-temperature lifespan CR2032 half-cell of the third embodiment of the present invention is generally the same as that of the first embodiment. The difference is that the soft carbon anode material in the conductive film of the anode is replaced by the anode carbon material (i.e., high-temperature lifespan soft carbon) prepared by the method of the third embodiment.

[0057] Assembly of High-Temperature Lifetime 18650 Full Cells

[0058] The assembly of the high-temperature lifespan 18650 full cell in the third embodiment of the present invention is generally the same as that in the first embodiment. The difference is that the soft carbon anode material in the conductive film of the anode is replaced by the anode carbon material (i.e., high-temperature lifespan soft carbon) prepared by the method of the third embodiment.

[0059] See also Figure 2 A fourth embodiment of the lithium-ion secondary battery 3 of the present invention is generally the same as the second embodiment, except that in the fourth embodiment of the lithium-ion secondary battery 3 of the present invention, the negative electrode 31 contains the negative electrode carbon material (i.e., high-capacity soft carbon) obtained by the manufacturing method of the fourth embodiment, thereby making the lithium-ion secondary battery 3 a high-capacity lithium-ion secondary battery.

[0060] Assembly of High-Capacity CR2032 Half-Cell (Button Cell)

[0061] The assembly of the high-lifetime CR2032 half-cell in the fourth embodiment of the present invention is generally the same as that in the first embodiment. The difference is that the soft carbon anode material in the conductive film of the anode is replaced by the anode carbon material (i.e., high-capacity soft carbon) prepared by the method of the fourth embodiment.

[0062] Assembly of high-capacity 18650 full batteries

[0063] The assembly of the high-capacity 18650 full cell in the fourth embodiment of the present invention is generally the same as that in the first embodiment, except that the soft carbon anode material in the conductive film of the anode is replaced by the anode carbon material (i.e., high-capacity soft carbon) prepared by the method of the fourth embodiment.

[0064] Half-cell performance testing

[0065] Using a charge / discharge tester (manufacturer: Arbin, model: BT2043), the first-cycle charging capacity and first-cycle discharging capacity of the CR2032 half-cells of each embodiment were measured. The test conditions were: temperature 25°C, charge / discharge rate (C-rate) of 0.2C, charging cutoff voltage of 0V, and discharging cutoff voltage of 1.8V. The percentage of irreversible capacity in the first cycle of the CR2032 half-cells of each embodiment was calculated using the following formula: Percentage of irreversible capacity in the first cycle = (First-cycle charging capacity - First-cycle discharging capacity) ÷ First-cycle charging capacity × 100%.

[0066] <Full Battery Performance Testing>

[0067] The charging and discharging capabilities of the general-type full battery (18650) of the first embodiment and the fast-charging full battery (7799130) of the second embodiment were measured at 25°C using a charge / discharge machine (manufacturer: Maccor, model: Series 4000). The test cycle was 1 cycle, and the capacity retention rate was measured at charging rates of 0.2C, 0.5C, 1C, 3C and 5C, and the capacity retention rate was measured at discharging rates of 0.1C, 0.5C, 3C, 5C, 8C and 10C.

[0068] The room temperature cycle life and high temperature cycle life of the 18650 full cells were measured using a charge / discharge machine (manufacturer: Maccor, model: Series 4000). The room temperature cycle life and high temperature cycle life of each 18650 full cell were measured at 25°C and 45°C, respectively, with a charge / discharge rate of 2C. The room temperature cycle life and high temperature cycle life were recorded with a capacity retention rate of 82% or 90% as the baseline.

[0069] See Figure 3 The diagram shows the charge-discharge curves of the half-cells of the first and second embodiments of the present invention. According to... Figure 3 The displayed charge-discharge curves summarize the first-cycle charge-discharge characteristics of the first and second embodiments, as shown in Table 2 below.

[0070] Table 2.

[0071]

[0072] From Table 2 above. Figure 3As shown, under 0.2C charge / discharge conditions, the irreversible capacity percentage of the fast-charging lithium-ion secondary battery (half-cell) is 13.75% [(320-276)÷320×100%], while the irreversible capacity percentage of the general lithium-ion secondary battery (half-cell) is 14.10% [(312-268)÷312×100%]. Therefore, the irreversible capacity percentages of the fast-charging lithium-ion secondary battery (half-cell) and the general lithium-ion secondary battery (half-cell) are similar, and the discharge capacity of the fast-charging lithium-ion secondary battery (half-cell) is 3% higher than that of the general lithium-ion secondary battery (half-cell) after conversion {[(276-268) / 268]×100%} and rounding.

[0073] See Figure 4 The image shows the capacity retention rates of a general-type lithium-ion secondary battery (full cell) according to the first embodiment of the present invention and a fast-charging lithium-ion secondary battery (full cell) according to the second embodiment at different charging rates. Figure 4 As shown, under 3C fast charging conditions, the capacity retention rate of this fast-charging lithium-ion secondary battery, after conversion [(88-83.5) / 83.5×100%=5.39%], is more than 5% higher than that of the general lithium-ion secondary battery. Furthermore, under 5C fast charging conditions, the capacity retention rate of this fast-charging lithium-ion secondary battery, after conversion [(84-76) / 76×100%=10.53%], is more than 10% higher than that of the general lithium-ion secondary battery.

[0074] See Figure 5 The image shows the capacity retention rates of a general-type lithium-ion secondary battery (full cell) according to the first embodiment of the present invention and a fast-charging lithium-ion secondary battery (full cell) according to the second embodiment at different discharge rates. Figure 5 As shown, under fast discharge conditions of 3C, 5C, 8C, and 10C, the percentage increase in capacity retention rate of the fast-charging lithium-ion secondary battery (full cell) compared to that of the general lithium-ion secondary battery (full cell), after conversion, are [(94-87) / 87×100%=8.05%], [(93.6-85.6) / 85.6×100%=9.35%], [(93.6-85.6) / 85.6×100%=9.35%], and [(92-85) / 85×100%=8.24%]. Therefore, under fast discharge conditions from 3C to 10C, the capacity retention rate of the fast-charging lithium-ion secondary battery (full cell) is increased by more than 8% compared to that of the general lithium-ion secondary battery (full cell).

[0075] Depend on Figure 4 and Figure 5 Analysis shows that in the grinding and grading step (C) of the method for preparing the negative electrode carbon material of the second embodiment of the present invention, the D50 is reduced from 10μm to 12μm in the first embodiment to 8μm to 10μm, and the D10 is reduced from 6μm to 8μm in the first embodiment to 3μm to 5μm. This can increase the specific surface area of ​​the batch of carbon-containing powder in step (C). Therefore, in the modification and carbonization step (E) of the method for preparing the negative electrode carbon material of the second embodiment, the amount of pitch that has reached its softening point and whose viscosity has decreased can be increased to fill the batch of carbon material powder, thereby reducing the specific surface area of ​​the fast-charging soft carbon obtained by the method of the second embodiment. The aforementioned results facilitate the formation of a stable solid electrolyte interface (SEI) film after the fast-charging soft carbon is processed, assembled into the fast-charging lithium-ion secondary battery (full cell), and activated. This improves the capacity retention rate of the fast-charging lithium-ion secondary battery (full cell) of the second embodiment during fast charging and fast discharging, thereby increasing the fast charging and fast discharging capabilities of the fast-charging lithium-ion secondary battery (full cell).

[0076] See Figure 6 The diagram shows the charge-discharge curves of the half-cells of the first and third embodiments of the present invention. According to... Figure 6 The displayed charge-discharge curves summarize the first-cycle charge-discharge characteristics of the first and third embodiments, as shown in Table 3 below.

[0077] Table 3.

[0078]

[0079] From Table 3 above, and Figure 6 As shown, under 0.2C charge and discharge conditions, the discharge capacity of this high-temperature life lithium-ion secondary battery (half-cell) is reduced by 15.9% relative to the irreversible capacity of this general lithium-ion secondary battery (half-cell) after conversion {[(44-37) / 44]×100%}.

[0080] See Figure 7 The display shows the room temperature cycle life test results of the general-type lithium-ion secondary battery (full cell) of the first embodiment of the present invention and the high-temperature life type lithium-ion secondary battery (full cell) of the third embodiment. Figure 7 As shown, under the cycle testing conditions of 2C fast charging, 2C fast discharging, 25°C and 4.2V to 2.4V, the cycle life of this high-temperature life lithium-ion secondary battery (full cell) is about 2000 cycles, which is greater than the cycle life of the general lithium-ion secondary battery (full cell) (about 1700 cycles).

[0081] See Figure 8 The display shows the high-temperature cycle life test results of the general-type lithium-ion secondary battery (full cell) of the first embodiment of the present invention and the high-temperature life type lithium-ion secondary battery (full cell) of the third embodiment. Figure 8 As shown, under the cycle testing conditions of 2C fast charging, 2C fast discharging, 45℃ and 4.2V to 2.4V, the cycle life of this high-temperature life lithium-ion secondary battery (full battery) with a capacity retention rate of 82% is calculated to be [(900 / 400)=2.25], which is at least 2.25 times that of the general lithium-ion secondary battery (full battery) with a capacity retention rate of 82%.

[0082] Depend on Figure 7 and Figure 8 Analysis shows that in the modification and carbonization step (E) of the preparation method of the negative electrode carbon material (i.e., high-temperature lifespan soft carbon) of the third embodiment of the present invention, the third heating rate is reduced from 1.22℃ / min in the first embodiment to 0.95℃ / min, and the modification and carbonization temperature is increased from 1100℃ in the first embodiment to 1200℃. This helps the asphalt to form a more stable carbon structure coating on the surface of the batch of carbon material powder during the modification and carbonization step (E). The aforementioned results are beneficial for the high-temperature lifespan soft carbon to form a more stable SEI film after processing and assembling into the high-temperature lifespan lithium-ion secondary battery (full cell) and completing activation. It is less likely to cause the formation of a new SEI film or the increase in the thickness of the original SEI film due to the destruction of the SEI film structure during long-term cycle life testing, which would lead to an increase in internal resistance and a decline in battery capacity, resulting in a worse cycle life. Therefore, the high-temperature cycle life of the high-temperature lifespan lithium-ion secondary battery (full cell) of the third embodiment can be improved during fast charging and fast discharging.

[0083] See Figure 9 The diagram shows the charge-discharge curves of the half-cells of the first and fourth embodiments of the present invention. According to... Figure 9 The displayed charge-discharge curves summarize the first-cycle charge-discharge characteristics of the first embodiment and the fourth embodiment, as shown in Table 4 below.

[0084] Table 4.

[0085]

[0086] From Table 4 above, and... Figure 9As shown, under 0.2C charge / discharge conditions, the irreversible capacity percentage of the high-capacity lithium-ion secondary battery (half-cell) is 15.54% [(341-288)÷341×100%], while the irreversible capacity percentage of the general lithium-ion secondary battery is 14.10% as mentioned above. Therefore, the irreversible capacity percentages of the high-capacity lithium-ion secondary battery (half-cell) and the general lithium-ion secondary battery (half-cell) are similar, and the discharge capacity of the high-capacity lithium-ion secondary battery (half-cell) is more than 7% higher than that of the general lithium-ion secondary battery (half-cell) after conversion {[(288-268) / 268]×100%}.

[0087] Depend on Figure 9 Analysis shows that in the preparation method of the negative electrode carbon material (i.e., high-capacity soft carbon) of the fourth embodiment of the present invention, in the modification carbonization step (E), the third heating rate is slightly reduced from 1.22℃ / min in the first embodiment to 1.16℃ / min, and the modification carbonization temperature is slightly reduced from 1100℃ in the first embodiment to 1050℃. This can change the carbon structure density of the batch of high-capacity soft carbon during the modification carbonization step (E); that is, the batch of high-capacity soft carbon has sp... 2 Hybrid orbital structure and a smaller portion of sp 3 Hybrid orbital structure, thus in sp 2 Hybrid orbital domain and sp 3 The hybrid orbitals provide extra space. It is worth noting that the aforementioned results facilitate the processing and assembly of this batch of high-capacity soft carbon into a high-capacity lithium-ion secondary battery (full cell) and its activation. This allows lithium ions to be inserted into / extracted from the soft carbon negative electrode material of the negative electrode conductive film through the aforementioned extra space, thereby increasing the capacity to hold lithium ions. Therefore, the discharge capacity of the high-capacity lithium-ion secondary battery (full cell) of this fourth embodiment can be improved.

[0088] See Figure 10 The display shows the room temperature cycle life test results of the general-type lithium-ion secondary battery (full cell) of the first embodiment of the present invention and the high-capacity lithium-ion secondary battery (full cell) of the fourth embodiment. Figure 10 As shown, under the cycle testing conditions of 2C fast charging, 2C fast discharging, 25°C and 4.2V to 2.4V, the high-capacity lithium-ion secondary battery (full battery) has a cycle life of approximately 1250 cycles with a capacity retention of 90% than the general lithium-ion secondary battery (full battery) with a capacity retention of 90% (only about 700 cycles).

[0089] See Figure 11The results show the high-temperature cycle life test results of the general-type lithium-ion secondary battery (full cell) of the first embodiment of the present invention and the high-capacity lithium-ion secondary battery (full cell) of the fourth embodiment. Figure 11 As shown, under the cycle testing conditions of 2C fast charging, 2C fast discharging, 45℃ and 4.2V to 2.4V, the cycle life of this high-capacity lithium-ion secondary battery (full battery) with a capacity retention rate of 82% is calculated to be [(900 / 560)=1.60], which is at least 1.5 times that of the general lithium-ion secondary battery (full battery) with a capacity retention rate of 82%.

[0090] In summary, the method for preparing the negative electrode carbon material of the present invention and its lithium-ion secondary battery, through the grinding and grading in step (C) to adjust the particle size distribution of the carbon powder (D50 and D10), and in conjunction with the third heating rate between 0.90°C / min and 1.25°C / min and the heating temperature range of 1030°C to 1220°C in step (E), can change the characteristics of the batch of asphalt-modified soft carbon obtained in step (E), thereby improving the rapid charge-discharge capability and cycle life of the batch of asphalt-modified soft carbon after being assembled into a lithium-ion secondary battery. Therefore, the purpose of the present invention can indeed be achieved.

[0091] The above description is merely an embodiment of the present invention and should not be construed as limiting the scope of the present invention. Any simple equivalent changes and modifications made in accordance with the claims and description of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a negative electrode carbon material, characterized in that: It is applicable to lithium-ion secondary batteries and includes the following steps in sequence: Step (A) involves heating a batch of heavy oil to turn it into a batch of raw coke; Step (B) involves heating the batch of raw coke to 850°C to 900°C at a first heating rate of 3°C to 5°C to 5°C and holding it at that temperature for at least 4 hours to make it a batch of carbon-containing material. Step (C) is to grind the batch of carbon-containing materials and classify a batch of carbon-containing powder with D50 between 8 μm and 12 μm and D10 between 1 μm and 8 μm from the ground carbon-containing materials. Step (D) involves heating the batch of carbon-containing powder to 1030°C to 1220°C at a second heating rate of 3°C / min to 10°C / min and holding it at that temperature for at least 4 hours, thereby forming a batch of carbon material powder; and Step (E) involves adding a predetermined amount of asphalt to the batch of carbon powder, then heating the batch of carbon powder with added asphalt to 1030°C to 1220°C at a third heating rate of 0.90°C / min to 1.25°C / min and holding it at that temperature for at least 5 hours, so that it becomes a batch of asphalt-modified soft carbon.

2. The method for preparing the negative electrode carbon material according to claim 1, characterized in that: In step (C), carbon powder with D50 between 10 μm and 12 μm and D10 between 6 μm and 8 μm is separated from the ground carbon-containing material. In step (D), the batch of carbon-containing powder is heated to 1080°C to 1120°C; and In step (E), the predetermined amount is at least 4 parts by weight, based on a total weight of 100 parts by weight of the carbon powder, and the batch of carbon powder with added asphalt is heated to 1080°C to 1120°C at a third heating rate of 1.20°C / min to 1.25°C / min, so that the batch of asphalt-modified soft carbon becomes a batch of general soft carbon.

3. The method for preparing the negative electrode carbon material according to claim 1, characterized in that: In step (C), carbon powder with D50 between 8 μm and 10 μm and D10 between 2 μm and 6 μm is separated from the ground carbon material. In step (D), the batch of carbon-containing powder is heated to 1080°C to 1120°C; and In step (E), the predetermined amount is at least 4 parts by weight, based on a total weight of 100 parts by weight of the carbon material powder, and the batch of carbon material powder with added asphalt is heated to 1080°C to 1120°C at a third heating rate of 1.20°C / min to 1.25°C / min, so that the batch of asphalt-modified soft carbon becomes a batch of fast-charging soft carbon.

4. The method for preparing the negative electrode carbon material according to claim 1, characterized in that: In step (C), carbon powder with D50 between 10 μm and 12 μm and D10 between 6 μm and 8 μm is separated from the ground carbon-containing material. In step (D), the batch of carbon-containing powder is heated to 1180°C to 1220°C; and In step (E), the predetermined amount is at least 4 parts by weight, based on a total weight of 100 parts by weight of the carbon powder, and the batch of carbon powder with added asphalt is heated to 1180°C to 1220°C at a third heating rate of 0.92°C / min to 0.98°C / min, so that the batch of asphalt-modified soft carbon becomes a batch of high-temperature life soft carbon.

5. The method for preparing the negative electrode carbon material according to claim 1, characterized in that: In step (C), carbon powder with D50 between 10 μm and 12 μm and D10 between 6 μm and 8 μm is separated from the ground carbon-containing material. In step (D), the batch of carbon-containing powder is heated to 1030°C to 1070°C; and In step (E), the predetermined amount is at least 4 parts by weight, based on a total weight of 100 parts by weight of carbon powder, and the batch of carbon powder with added asphalt is heated to 1030°C to 1070°C at a third heating rate of 1.12°C / min to 1.18°C / min, so that the batch of asphalt-modified soft carbon becomes a batch of high-capacity soft carbon.

Images