A lithium-ion battery

Abstract

This invention proposes a lithium-ion battery, belonging to the field of battery technology. The positive electrode material is prepared from raw materials comprising the following parts by weight: 50-90 parts of lithium manganese iron phosphate; 5-25 parts of lithium nickel cobalt manganese oxide; and 5-25 parts of lithium manganese oxide. The lithium-ion battery positive electrode material proposed in this invention uses a scientific blend of lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, and lithium manganese oxide, with lithium manganese iron phosphate as the main component and lithium nickel cobalt manganese oxide and lithium manganese oxide as auxiliary components. The particles are deeply composited through ball milling, thereby transforming the double-plateau discharge curve of lithium manganese iron phosphate into a smooth and gentle curve. Using this material to prepare lithium-ion batteries results in lithium batteries with high energy density, good safety performance, good cycle life, and low cost.

Description

[0001] This application is a divisional application. The parent invention is entitled "A Lithium-ion Battery Positive Electrode Material, Positive Electrode Sheet and Lithium-ion Battery", with application number 202010960586.1 and application date 2020-09-14. Technical Field

[0002] This invention belongs to the field of battery technology, and particularly relates to a lithium-ion battery. Background Technology

[0003] As people's living standards continue to improve, the demand for batteries is constantly increasing, especially for reusable lithium-ion batteries.

[0004] Lithium manganese iron phosphate (LMP) is a commonly used cathode material for lithium-ion batteries. It is low in cost and environmentally friendly. Like lithium iron phosphate, it belongs to the olivine crystal form and has the same theoretical capacity and excellent safety performance. Its theoretical capacity is the same as that of lithium iron phosphate (170 mAh / g). Compared with graphite anode, it has two discharge platforms (3.85V and 3.35V). The high potential of 4.0V gives LMP the potential for high energy density. However, the voltage difference between the two platforms is nearly 0.5V. The high voltage difference can cause a huge impact on electrical equipment, which greatly limits the industrial application of LMP.

[0005] For example, CN106129365A discloses a high-safety lithium manganese iron phosphate battery, which mainly uses lithium nickel cobalt manganese oxide as the primary material and lithium manganese iron phosphate as an auxiliary material. A simple mechanical-physical mixing method is used to improve and enhance the thermal stability of the lithium nickel cobalt manganese oxide material, thereby improving its safety performance. However, this invention only uses lithium manganese iron phosphate as an auxiliary material, making it impossible to mass-produce lithium manganese iron phosphate for industrialization.

[0006] CN105449269A discloses a lithium-ion battery that combines lithium iron phosphate, lithium nickel cobalt manganese oxide, and lithium manganese iron phosphate to improve the battery's cycle performance, energy density, and safety performance. However, this invention still uses lithium manganese iron phosphate as an auxiliary material, and the voltage platforms of lithium nickel cobalt manganese oxide and lithium manganese iron phosphate are both higher than 3.6V, while the discharge platform of lithium iron phosphate is only 3.2V. The voltage platforms of the three materials are not well matched, which prevents the battery from fully realizing its optimal performance. Summary of the Invention

[0007] This invention proposes a lithium-ion battery cathode material, cathode sheet, and lithium-ion battery to solve the above-mentioned technical problems.

[0008] This invention proposes a lithium-ion battery cathode material, prepared from raw materials comprising the following parts by weight:

[0009] Lithium manganese iron phosphate 50-90 parts; lithium nickel cobalt manganese oxide 5-25 parts; lithium manganese oxide 5-25 parts;

[0010] The total number of samples included is 100 for lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, and lithium manganese oxide.

[0011] Further, the D50 of the lithium manganese iron phosphate is 0.7-1.5 μm; the D50 of the lithium nickel cobalt manganese oxide is 8.0-15.0 μm; and the D50 of the lithium manganese oxide is 8.0-15.0 μm.

[0012] Furthermore, the lithium manganese iron phosphate is LiMn. x Fe (1-x) PO4, where 0.5 ≤ x ≤ 0.8;

[0013] The lithium nickel cobalt manganese oxide is LiNi x Mn y Co (1-x-y) O2, where 0 < x < 1, 0 < y < 1, 0 < 1 - xy < 1;

[0014] The lithium manganese oxide is LiMn2O4.

[0015] The present invention also proposes a method for preparing a positive electrode material for lithium-ion batteries, comprising: mixing the above-mentioned raw materials lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, and lithium manganese oxide, placing them in a ball mill jar, adding zirconium balls, and then ball milling to obtain the positive electrode material.

[0016] Furthermore, the diameter of the zirconium balls is 10–20 mm, the ball-to-material mass ratio is 2:1–4:1, and the ball milling time is 20–40 min.

[0017] The present invention also proposes a positive electrode sheet, comprising a current collector and a positive electrode active material layer coated on the current collector, wherein the positive electrode active material layer comprises any of the above-mentioned positive electrode materials.

[0018] The present invention also proposes a lithium-ion battery, comprising: a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is the aforementioned positive electrode or includes any of the aforementioned positive electrode materials.

[0019] Furthermore, the membrane material is polyethylene, polypropylene, or a polypropylene-polyethylene-polypropylene three-layer composite membrane.

[0020] This invention has the following advantages:

[0021] (1) The lithium-ion battery cathode material proposed in this invention is made by scientifically compounding lithium manganese iron phosphate, lithium nickel cobalt manganese oxide and lithium manganese oxide. Lithium manganese iron phosphate is the main component and lithium nickel cobalt manganese oxide and lithium manganese oxide are auxiliary components. The particles are deeply compounded by ball milling, so that the double plateau of lithium manganese iron phosphate discharge becomes a smooth and stable curve. When used to prepare lithium-ion batteries, lithium batteries with high energy density, good safety performance, good cycle life and low cost can be obtained.

[0022] (2) In this invention, the particle size D50 of lithium manganese iron phosphate is 0.7 to 1.5 μm, and the particle size D50 of lithium nickel cobalt manganese oxide and lithium manganese oxide is 8 to 15 μm. The small-particle-size olivine crystal type lithium manganese iron phosphate can fill the gaps in the large-particle-size layered lithium nickel cobalt manganese oxide and spinel crystal type lithium manganese oxide materials. In this way, the dual-platform discharge problem of lithium manganese iron phosphate is solved, and the energy density, safety performance and cycle life of the battery are also improved. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0024] In the attached diagram:

[0025] Figure 1 The image shown is a scanning electron microscope (SEM) image of the composite material obtained in Example 1 of this invention.

[0026] Figure 2 This is a transmission electron microscope (TEM) image of the composite material obtained in Example 1 of the present invention;

[0027] Figure 3 The discharge curves are for Embodiment 3 and Comparative Examples 3 and 4 of the present invention.

[0028] Figure 4 This is the cycle curve of the battery in Embodiment 3 of the present invention. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0030] In existing technologies, the main component of commonly used lithium-ion battery cathode materials is lithium nickel cobalt manganese oxide, which has high energy density but poor safety performance and is expensive. Another commonly used cathode material component is lithium manganese iron phosphate, which is low in cost and environmentally friendly, and has the same theoretical capacity and excellent safety performance as lithium iron phosphate. However, due to its dual discharge plateau (the voltage difference between the two plateaus is nearly 0.5V), it can only be used as an auxiliary component in combination with lithium nickel cobalt manganese oxide, which severely limits its application.

[0031] The lithium-ion battery cathode material proposed in this invention comprehensively considers the performance and discharge platform of different cathode materials. It scientifically combines lithium manganese iron phosphate (discharge platform of 3.85V and 3.35V), lithium nickel cobalt manganese oxide (discharge platform of 3.65V), and lithium manganese oxide (discharge platform of 3.85V), with lithium manganese iron phosphate as the main component and lithium nickel cobalt manganese oxide and lithium manganese oxide as auxiliary components. By comprehensively considering the voltage difference and electrical performance of each component's platform, the resulting cathode material can effectively solve the dual-platform problem. When used to prepare lithium-ion batteries, lithium batteries with high energy density, good safety performance, good cycle life, and low cost can be obtained.

[0032] Specifically, one embodiment of the present invention provides a lithium-ion battery cathode material, which is prepared from raw materials comprising the following parts by weight:

[0033] Lithium manganese iron phosphate 50-90 parts; lithium nickel cobalt manganese oxide 5-25 parts; lithium manganese oxide 5-25 parts;

[0034] The total number of samples included is 100 for lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, and lithium manganese oxide.

[0035] In one embodiment of the present invention, the D50 of the lithium manganese iron phosphate is 0.7-1.5 μm; the D50 of the lithium nickel cobalt manganese oxide is 8.0-15.0 μm; and the D50 of the lithium manganese oxide is 8.0-15.0 μm.

[0036] In one embodiment of the present invention, the lithium manganese iron phosphate is LiMn. x Fe (1-x) PO4, where 0.5 ≤ x ≤ 0.8.

[0037] The lithium nickel cobalt manganese oxide is LiNi x Mn y Co (1-x-y) O2, where 0 < x < 1, 0 < y < 1, 0 < 1 - xy < 1; specifically, it can be NCM111, NCM523, NCM622, or NCM811.

[0038] The lithium manganese oxide is LiMn2O4.

[0039] Another embodiment of the present invention provides a method for preparing a positive electrode material for lithium-ion batteries, comprising: mixing the above-mentioned raw materials lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, and lithium manganese oxide, placing them in a ball mill jar, adding zirconium balls, and then ball milling to obtain the positive electrode material.

[0040] Specifically, the diameter of the zirconium balls is 10–20 mm. The ball-to-material mass ratio is 2:1–4:1. The ball milling time is 20–40 min. Preferably, the diameter of the zirconium balls is 15 mm. The ball-to-material mass ratio is 2:1. The ball milling time is 30 min.

[0041] An embodiment of the present invention also provides a positive electrode sheet, comprising a current collector and a positive electrode active material layer coated on the current collector, wherein the positive electrode active material layer comprises the aforementioned positive electrode material.

[0042] Specifically, the positive electrode active material layer is composed of raw materials comprising the following parts by weight:

[0043] 92-96 parts of positive electrode material;

[0044] 2-4 parts of positive electrode conductive agent;

[0045] 2-4 parts of positive electrode binder;

[0046] Preferred;

[0047] The positive electrode conductive agent is at least one of conductive carbon black, conductive graphite, carbon nanotubes, or graphene.

[0048] The positive electrode adhesive is at least one of Solvay PVDF 5130 and Arkema PVDF 900.

[0049] An embodiment of the present invention also provides a lithium-ion battery, comprising: a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is any of the above-mentioned positive electrode or includes any of the above-mentioned positive electrode materials.

[0050] Preferably, the negative electrode sheet includes a current collector and a negative electrode active material layer coated on the current collector, the negative electrode active material layer being composed of raw materials comprising the following parts by weight:

[0051] 94-96 parts of negative electrode material;

[0052] 1-2 parts of negative electrode conductive agent;

[0053] 3-4 parts of negative electrode binder.

[0054] More preferably, the negative electrode material is artificial graphite or natural graphite;

[0055] The negative electrode adhesive is at least one of styrene-butadiene rubber or sodium carboxymethyl cellulose.

[0056] Furthermore, the membrane material is polyethylene, polypropylene, or a polypropylene-polyethylene-polypropylene three-layer composite membrane.

[0057] The present invention will now be described in detail with reference to the embodiments.

[0058] Example 1 A lithium-ion battery cathode material and its preparation method

[0059] The cathode material includes:

[0060] The lithium manganese iron phosphate comprises 70 parts by weight, wherein the lithium manganese iron phosphate uses LiMn. 0.6 Fe 0.4 PO4;

[0061] The mass fraction of lithium nickel cobalt manganese oxide is 20 parts, wherein the lithium nickel cobalt manganese oxide is LiNi 0.5 Mn 0.3 Co 0.2 O2;

[0062] The mass fraction of lithium manganese oxide is 10 parts.

[0063] The three materials were mixed and placed in a 2L polyurethane ball mill jar. Zirconium balls with a diameter of 15mm were added, and the ball-to-material ratio was 2:1. The ball mill jar was placed in a ball mill with the frequency adjusted to 30HZ and the milling time was 30min to obtain the composite lithium manganese iron phosphate material for later use.

[0064] Its scanning electron microscope morphology image is shown below Figure 1 Transmission electron microscope morphology images are shown below. Figure 2 .

[0065] Example 2 A lithium-ion battery cathode material and its preparation method

[0066] The cathode material includes:

[0067] The lithium manganese iron phosphate comprises 80 parts by weight, wherein the lithium manganese iron phosphate is made from LiMn. 0.6 Fe 0.4 PO4;

[0068] The mass fraction of lithium nickel cobalt manganese oxide is 10 parts, wherein the lithium nickel cobalt manganese oxide is LiNi 0.5 Mn 0.3 Co 0.2 O2;

[0069] The mass fraction of lithium manganese oxide is 10 parts.

[0070] The three materials were mixed and placed in a 2L polyurethane ball mill jar. Zirconium balls with a diameter of 15mm were added, and the ball-to-material ratio was 2:1. The ball mill jar was placed in a ball mill with the frequency adjusted to 30HZ and the milling time was 30min to obtain the composite lithium manganese iron phosphate material for later use.

[0071] Example 3 A lithium-ion battery

[0072] A lithium-ion battery includes: a positive electrode, a negative electrode, a separator, and an electrolyte;

[0073] The positive electrode sheet includes a current collector and a positive electrode active material layer coated on the current collector; the positive electrode active material layer is composed of the following raw materials in parts by weight: 95 parts of the positive electrode material obtained in Example 1; 3 parts of the positive electrode conductive agent; 2 parts of the positive electrode binder (Sowes PVDF 5130);

[0074] The negative electrode sheet includes a current collector and a negative electrode active material layer coated on the current collector. The negative electrode active material layer is composed of the following raw materials in parts by weight: 95 parts of negative electrode material (artificial graphite); 1 part of negative electrode conductive agent; and 4 parts of negative electrode binder (styrene-butadiene rubber).

[0075] The diaphragm is made of polyethylene.

[0076] Example 4 A lithium-ion battery

[0077] Same as Example 3, except that the positive electrode material obtained in Example 2 is used.

[0078] Comparative Example 1 A lithium-ion battery cathode material and its preparation method

[0079] Similar to Example 1, except that the cathode material includes only lithium manganese iron phosphate, that is, the mass fraction of lithium manganese iron phosphate is 100 parts.

[0080] Comparative Example 2 A lithium-ion battery cathode material and its preparation method

[0081] Same as Example 1, except that lithium iron phosphate (discharge platform 3.2V) is used instead of lithium nickel cobalt manganese oxide for the positive electrode material, i.e., lithium manganese iron phosphate (LiMnFePO4). 0.6 Fe 0.4 The mass fraction of PO4 is 70 parts, the mass fraction of lithium iron phosphate is 20 parts, and the mass fraction of lithium manganese oxide is 10 parts.

[0082] Comparative Example 3 A lithium-ion battery

[0083] Same as Example 3, except that the cathode material obtained in Comparative Example 1 is used.

[0084] Comparative Example 4 A lithium-ion battery

[0085] Same as Example 4, except that the cathode material obtained in Comparative Example 2 is used.

[0086] Experimental Example 1

[0087] The electrical performance of the full cells obtained in Examples 3-4 and Comparative Examples 3-4 was tested, and the results are shown in Table 1.

[0088] Table 1

[0089]

[0090] Depend on Figure 3 It can be seen that the discharge curves of Comparative Examples 3 and 4 show obvious double plateaus, while the discharge curve of Example 3 is smoother and flatter than that of pure lithium manganese iron phosphate in Comparative Example 3, and no obvious double plateau curve is observed. Therefore, combining these three not only solves the double discharge plateau problem but also improves electrical performance testing and compaction density. If lithium manganese iron phosphate is only combined with one of lithium nickel cobalt manganese oxide or lithium manganese oxide, the limitations of either lithium nickel cobalt manganese oxide (such as its high cost and poor safety performance, and lithium manganese oxide's poor cycle performance and low capacity) will inevitably affect the overall performance of lithium manganese iron phosphate.

[0091] Furthermore, as shown in Table 1, the compaction density of the three cathode materials in Examples 3 and 4, after being compounded by ball milling in a certain proportion, was significantly improved. The compaction density of Example 3 reached 3.2 g / cm³. 3 .Depend on Figure 1 and Figure 2 It can also be seen that small-particle-size lithium manganese iron phosphate is coated and filled into large-particle-size ternary and lithium manganese oxide. The appropriate particle size distribution and ball milling composite process make the composite material have a higher volumetric energy density.

[0092] Furthermore, the 0.2C discharge specific capacity of Example 3 was 152.1 mAh / g, and the median voltage was 3.6864 V. The specific capacity of the material was higher than the theoretical specific capacity based on the proportional composite. Because the three materials were deeply composited through ball milling, the contact nodes between particles were more dense and uniform. Microscopically, Mn in the composite material had +2, +3, and +4 valence states. The synergistic effect of the composite material resulted in a better discharge plateau curve and higher energy density. Moreover, the battery of Example 3 maintained a capacity retention of 86.8% after 2000 cycles at 1C, and its cycle performance was far superior to that of lithium nickel cobalt manganese oxide and lithium manganese oxide. Figure 4 ).

[0093] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, comprising: The positive electrode sheet, the negative electrode sheet, the diaphragm and the electrolyte are characterized in that The positive electrode sheet comprises a current collector and a positive active material layer coated on the current collector, wherein the positive active material layer comprises a positive material; The positive material is prepared from raw materials comprising the following proportions by weight: 50-90 parts of lithium iron manganese phosphate, 5-25 parts of lithium nickel cobalt manganese oxide, and 5-25 parts of lithium manganate, wherein the total of lithium iron manganese phosphate, lithium nickel cobalt manganese oxide and lithium manganate is 100 parts; The D50 of the lithium iron manganese phosphate is 0.7-1.5 μm, the D50 of the lithium nickel cobalt manganese oxide is 8.0-15.0 μm, and the D50 of the lithium manganate is 8.0-15.0 μm; LiFe x PO4, wherein 0.5≤x≤0.8; the lithium nickel cobalt manganese oxide is LiNi x Mn y Co (1-x-y) O2, wherein 0 The positive electrode sheet, the negative electrode sheet, the diaphragm and the electrolyte are characterized in that Mn2O4. The preparation method of the positive material comprises: mixing the above-mentioned raw materials of lithium iron manganese phosphate, lithium nickel cobalt manganese oxide and lithium manganate, placing them in a ball mill tank, and then ball milling the mixture after adding zirconium balls to obtain the positive material.

2. The lithium ion battery according to claim 1, characterized in that The diameter of the zirconium balls is 10-20 mm, the ball-to-material mass ratio is 2:1-4:1, and the ball milling time is 20-40 min.

3. The lithium ion battery according to claim 1, characterized in that The diaphragm material is polyethylene, polypropylene or a polypropylene-polyethylene-polypropylene three-layer composite diaphragm.

Images