Lithium battery positive electrode material and preparation method thereof, and lithium battery using the positive electrode material

Abstract

The present invention discloses a cathode material for a lithium-ion battery. The cathode material is a lithium oxide, and the cathode material is composed of spherical secondary particles formed by primary particles of the lithium oxide. The average particle size of the primary particles is 100-200 nm, and a pore structure is distributed in the secondary particles, with the pore diameter being 1-2 μm. The chemical formula of the cathode material is Li 1+x M 1‑x O2, where x = 0.05-0.25, and M is one or more of Ni, Co, Mn, Al, Mg, Fe, Ti, Cr, Ga, Zn, V, Ge, and Sn. The cathode material for the lithium-ion battery in the present invention has high density, high activity, and high charge-discharge stress and strain. The present invention also provides a preparation method for the cathode material for the lithium-ion battery. This method not only increases the uniformity of the raw material mixture but also improves the activity of the cathode material, and macroscopically improves the cycle stability of the cathode material for the lithium-ion battery during the charge-discharge process.

Description

Technical Field

[0001] The present invention belongs to the field of lithium ion battery manufacturing, and specifically relates to a lithium ion battery positive electrode material and a method for preparing the positive electrode material, and also relates to a lithium ion battery using the positive electrode material as the battery positive electrode material. Background Art

[0002] Compared with traditional secondary batteries, lithium-ion batteries (referred to as "lithium batteries") have the advantages of high platform voltage (up to 3.2-3.7V), high energy density, and no memory effect. Therefore, they have been widely used in electronic products such as smart phones, cameras, and computers. Lithium-ion secondary batteries are not only used in the field of 3C products, but also widely used in industrial fields such as electric vehicles and uninterruptible power supplies. Lithium-ion batteries are mainly composed of a positive electrode of lithium alloy oxide, a liquid organic electrolyte or a solid electrolyte, and a negative electrode material. Among them, the positive electrode material is an important component of lithium-ion batteries, and its performance is the main factor affecting the quality of the battery. In the case that the gram capacity of the negative electrode of lithium-ion batteries in the existing technology is generally greater than 300mAh / g, how to improve the performance of the positive electrode material is an important research direction for improving the performance of lithium-ion batteries.

[0003] In the prior art, commercial lithium-ion batteries mainly use LiMO 2 As the positive electrode material, M is a metal ion such as Ni, Mn, Co, Al, etc., LiMO 2 It is a layered positive electrode material with extremely high theoretical capacity, which can meet the needs of high energy density lithium-ion batteries. Moreover, this type of material can be prepared by a simple solid-state sintering method, which is low-cost and simple in preparation process. 2 It has high capacity and stability, but is still not ideal in terms of environmental protection and economy. The most important influencing factors are as follows:

[0004] 1. LiMO prepared by solid phase sintering method 2 It is difficult to mix the raw materials of layered positive electrode materials completely and evenly during the sintering process, which leads to the segregation of metal ions in the raw materials and ion mixing. The mixed metal ions enter the lithium layer and hinder the transmission of lithium ions, thereby reducing the gram capacity of the positive electrode material.

[0005] 2. LiMO made by traditional solid phase sintering method 2 The secondary particles of the positive electrode material are relatively dense and have a low specific surface area. After being made into a battery, the contact area with the electrolyte is limited, resulting in low electrochemical reaction activity, further reducing the actual gram capacity.

[0006] 3. LiMO prepared by traditional methods 2During the charge and discharge cycle, the positive electrode material particles are insufficiently resistant to the stress and strain of charge and discharge, and cannot withstand the strong stress and strain caused by the deintercalation of lithium ions in the battery, and are prone to rupture. The broken particles cannot continuously transport lithium ions and electrons, which causes the internal resistance of the battery to increase and the battery capacity to decrease.

[0007] Although the above problems have been confirmed in many literatures, they have not been effectively improved in the actual research and development of lithium-ion battery positive electrode materials. The reason is that the current application bottleneck of lithium-ion batteries is still mainly focused on energy density. As long as the energy density is improved, the efficiency of lithium-ion batteries is improved. Theoretically, preparing positive electrode materials with denser particles can effectively improve the energy density. However, the denser the particles of the positive electrode material, the more obvious the above-mentioned problems of low specific surface area of ​​the particles and insufficient charge and discharge stress strain are, making it impossible for the development of lithium-ion positive electrode materials to make practical progress. Summary of the invention

[0008] In order to solve the deficiencies of the prior art, the present invention proposes another method for preparing positive electrode materials with different ideas. The same way as the prior art to improve the energy density of positive electrode materials for lithium-ion batteries, the present invention also adopts a solid phase sintering method to prepare positive electrode materials for lithium-ion batteries, so that the prepared positive electrode material particles have compactness and high energy density. On the other hand, starting from the preparation method, adding volatile organic acids and organic polymers before the solid phase sintering process not only increases the uniformity of raw material mixing, greatly reduces the possibility of metal ion segregation in the raw materials, and reduces the degree of ion mixing in the product. At the same time, the organic polymer leaves a uniform pore structure due to decomposition during the sintering process, which not only provides a channel for electrolyte infiltration to improve the activity of the positive electrode material, but also forms a buffer area for the positive electrode material to cope with stress and strain during the lithium ion deintercalation process, which macroscopically improves the cycle stability of the positive electrode material of the lithium-ion battery during the charging and discharging process.

[0009] The technical effects to be achieved by the present invention are achieved through the following solutions:

[0010] The lithium-ion battery positive electrode material provided in the present invention is lithium oxide, which is composed of spherical secondary particles composed of primary particles of lithium oxide, the average particle size of the primary particles is 100-200nm, and the secondary particles are distributed with pore structures, and the pore diameter is 1-2μm.

[0011] The lithium ion battery positive electrode material provided in the present invention has the chemical formula Li 1+x M 1-x O 2, wherein x=0.05-0.25, and M is one or more of Ni, Co, Mn, Al, Mg, Fe, Ti, Cr, Ga, Zn, V, Ge, and Sn.

[0012] Compared with the cathode materials in the prior art which have dense particles and thus theoretically have high energy density, the present invention adopts lithium oxide particles with a multi-porous structure as the cathode material. The cathode material not only provides a channel for electrolyte infiltration through the arrangement of the pore structure, thereby improving the activity of the cathode material, but also the pore structure forms a buffer area for the cathode material to cope with stress and strain during the lithium ion insertion and extraction process, thereby macroscopically improving the cycle stability of the cathode material of the lithium ion battery during the charge and discharge process.

[0013] The present invention also provides a method for preparing a positive electrode material for a lithium ion battery, comprising the following steps:

[0014] S01: Mix the metal salt and the lithium salt in a molar ratio of metal ion to lithium ion of 1:(1-1.3), add a volatile organic acid, wherein the amount of the volatile organic acid added is an amount capable of complexing all the metal salts in the raw materials with the metal ions in the lithium salt, and mix the three and grind them evenly;

[0015] In the sintering process of metal salts and lithium salts in the prior art, it is often impossible to obtain a completely uniform mixture through physical stirring or dispersion, resulting in the uniformity of the sintered product being limited by the effect of the dispersion process. In the present invention, a volatile organic acid is added during the mixing process of the two. The volatile organic acid can effectively complex the metal ions in the metal salt and the lithium ions in the lithium salt, so that the two can be more closely combined by intermolecular forces while being mechanically mixed, thereby achieving a good degree of mixing. Due to its volatility, the volatile organic acid will not cause residues in the raw materials and will not affect the composition of the raw materials.

[0016] Since volatile organic acids are volatile and leave no residue, the amount of volatile organic acids added does not need to be too limited. It is sufficient that the volatile organic acids can complex all metal salts in the raw materials and lithium ions in lithium salts. In actual use, excess addition is sufficient.

[0017] S02: The ground product in S01 is mixed with an organic polymer in an amount of 1-3 mL per gram of ground product and ground evenly;

[0018] Adding an organic polymer further makes the metal salt and the lithium salt mix evenly, enhances the uniformity of the raw material mixing, reduces the possibility of ion segregation, and reduces the degree of ion mixing in the product. More importantly, the organic polymer burns out under high temperature conditions during the subsequent sintering process, and the organic matter decomposes and produces gas during the burning process, thereby forming a pore structure in the microstructure of the positive electrode material in the present invention. Under this premise, it is necessary to select a suitable organic polymer. The organic polymer that produces too much gas during the burning process or produces ash residue cannot be used. In the present invention, it is preferred to use one or more compositions of polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 2000, polyethylene glycol 6000, and polyethylene glycol 12000.

[0019] S03: The ground product in S02 is pre-sintered at 300-500° C. for 4-10 hours.

[0020] S04: Sinter the pre-sintered product in S03 at 750-950° C. for 6-15 hours, and obtain the desired lithium-ion battery positive electrode material after cooling.

[0021] Compared with the prior art, the present invention enhances the uniformity of raw material mixing by adding volatile organic acid and liquid organic polymer during the synthesis process, reduces the possibility of ion segregation, reduces the degree of ion mixing in the product, and enhances the lithium ion transmission speed. At the same time, after the polymer is decomposed, a uniform pore structure is left. Such a porous structure can provide a channel for electrolyte infiltration on the one hand, enhance the electrochemical activity of the material, and on the other hand, buffer the stress and strain caused by the removal and embedding of lithium ions during the charge and discharge process, ensure the structural integrity, and thus stabilize the cycle performance of the positive electrode material.

[0022] The grinding time in S01 and S02 depends on the amount of raw materials, generally ranging from 0.5 to 10 hours. The more raw materials, the longer the grinding time. The purpose of grinding is to make the raw materials evenly mixed and the raw materials have uniform particle size. Similarly, the time of pre-sintering and sintering is adjusted according to the difficulty of decomposing the salts and the total amount of raw materials to be sintered. The more difficult the salts are to decompose and the larger the total amount of raw materials to be sintered, the longer the sintering time.

[0023] Furthermore, in S03, the pre-sintering temperature is 380-420°C; in S04, the sintering temperature is 800-850°C.

[0024] The present invention also provides a lithium ion battery using the above positive electrode material as the positive electrode material of the battery. Under the test condition of a cycle test voltage of 0.05-5C, the capacity retention rate of the lithium ion battery after 50 weeks of testing is greater than 94%, and the capacity retention rate after 100 weeks of testing is greater than 88%.

[0025] The present invention has the following advantages:

[0026] 1. The lithium-ion battery cathode material of the present invention has high density, high activity, and high charge and discharge stress strain.

[0027] 2. The preparation method of the positive electrode material for lithium-ion batteries in the present invention adds volatile organic acids and organic polymers before the solid-phase sintering process, which not only increases the uniformity of the mixing of raw materials, greatly reduces the possibility of metal ion segregation in the raw materials, and reduces the degree of ion mixing in the product, but also leaves a uniform pore structure due to decomposition during the sintering process of the organic polymer, which not only provides a channel for electrolyte infiltration and thus improves the activity of the positive electrode material, but also the pore structure forms a buffer area for the positive electrode material to cope with stress and strain during the lithium ion insertion and extraction process, thereby macroscopically improving the cycle stability of the positive electrode material of the lithium-ion battery during the charge and discharge process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The XRD scanning patterns of the positive electrode materials in Example 1 and Comparative Example 1 of the positive electrode material for lithium ion batteries of the present invention;

[0029] Figure 2 Field emission scanning electron microscope scanning spectra (S-4300 Shimadzu, 15 kV) of the positive electrode materials of lithium ion battery in Example 1 and Comparative Example 1 of the present invention, wherein ab is the particle morphology of the material in Comparative Example 1, and cf is the particle morphology of the material in Example 1;

[0030] Figure 3 The first week charge and discharge curves of the batteries made of the positive electrode materials in Example 1 and Comparative Example 1 of the lithium ion battery positive electrode material of the present invention;

[0031] Figure 4 The capacity differential curves corresponding to the first-week charge-discharge curves of the batteries made of the positive electrode materials in Example 1 and Comparative Example 1 of the lithium-ion battery positive electrode material of the present invention;

[0032] Figure 5 The cycle performance test curves of the batteries made of the positive electrode materials in Examples 1 and 5 of the lithium-ion battery positive electrode materials of the present invention and the positive electrode materials in Comparative Example 1 (test condition 0.2C);

[0033] Figure 6 The cycle performance test curves of the batteries made of the positive electrode materials in Examples 1 and 5 of the lithium-ion battery positive electrode materials of the present invention and the positive electrode materials in Comparative Example 1 (test condition 0.5C);

[0034] Figure 7 The cycle performance test results of the batteries made of the positive electrode materials in Examples 6 and 7 of the lithium-ion battery positive electrode materials of the present invention and the positive electrode materials in Comparative Example 1 (test condition 0.5C);

[0035] Figure 8 The cycle performance test results of the batteries made of the positive electrode materials in Examples 8 and 9 of the lithium-ion battery of the present invention and the positive electrode materials in Comparative Example 1 (test condition 0.5C);

[0036] Fig. 9 The cycle performance test results of the batteries made of the positive electrode materials in Examples 10, 11, 12 and Example 5 of the lithium ion battery positive electrode material of the present invention and the positive electrode materials in Comparative Example 1 (test condition 0.5C);

[0037] Fig.10 The microscopic morphology of the positive electrode material particles of the battery made of the positive electrode material in Example 1 and Comparative Example 1 of the lithium ion battery positive electrode material of the present invention after 50 cycles at 0.2C. DETAILED DESCRIPTION

[0038] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0039] The raw material components and raw material molar amounts / volumes of the lithium ion battery positive electrode material preparation process in the embodiment are as described in the following table:

[0040]

[0041]

[0042]

[0043] The preparation method of the positive electrode material in the embodiment is:

[0044] S01: Mix metal salt, lithium salt and volatile organic acid according to the ratio and grind for 5 hours;

[0045] S02: The ground product in S01 is mixed with an organic polymer and ground for 2 hours;

[0046] S03: pre-sintering the ground product in S02;

[0047] S04: Sintering the pre-sintered product in S03, and obtaining the desired positive electrode material for a lithium-ion battery after cooling.

[0048] The parameters in the specific preparation method are as follows:

[0049]

[0050] The prepared positive electrode material was made into a CR2016 button battery, wherein the positive electrode was a mixture of 80wt% positive electrode material, 10wt% pvdf, and 10wt% acetylene black, the counter electrode was a lithium sheet, the separator was Celgard 2500, and the electrolyte composition was 1M LiPF6 Dissolved in an organic solution with EC:DEC=1:1. Charge the fresh battery at 25℃ with a current of 0.2C until the voltage reaches 4.3 V, and discharge the charged battery with a current of 0.2C until the voltage reaches 2.8V. This discharge capacity is recorded as the first discharge capacity. The button battery was cycled for 50 and 100 weeks at 0.2C / 0.2C and 0.5C / 0.5C respectively. The test results are as follows:

[0051]

[0052] Figure 1 The XRD scanning patterns of the positive electrode materials in Example 1 and Comparative Example 1 are shown. The lattice structure of the material powder was analyzed using a Shimadzu XRD-6000 X-ray diffractometer (Cu-Kα radiation, λ = 1.5418 Å), with a scanning angle 2θ of 10-80° and a scanning speed of 1° / min. Figure 1 It can be seen that both materials have similar R-3m structures, but the different ratios of the two peak intensities (003) and (104) indicate different ion mixing. The higher the ratio of I(003) / I(104), the less ion mixing there is in the positive electrode material. Figure 1 It can be calculated that I(003) / I(104) in Example 1 (PA) is 1.346, while I(003) / I(104) in Comparative Example 1 (SS) is 1.207. This result shows that the material obtained in this example has a low degree of ion mixing and has a higher lithium ion transmission rate.

[0053] Figure 2 The field emission scanning electron microscope scanning spectra of the positive electrode materials in Example 1 and Comparative Example 1 are observed by field emission scanning electron microscope (S-4300 Shimadzu, 15 kV). Figure 2 Figures ab show that the material of comparative example 1 has dense secondary particles, and the size of its primary particles varies from 100 to 500 nm. Figure cf shows that the secondary particles of the material of Example 1 are composed of a large number of primary particles with uniform particle size (100-200 nm). There are many pore structures distributed on the secondary particles of Example 1, and the size of the pores is about 1-2 μm. These pores are formed by the decomposition of the polymer during the sintering process to generate gas.

[0054] Figure 3 and Figure 4The first week charge and discharge curves and the corresponding capacity differential curves of the batteries made of the positive electrode materials in Example 1 and Comparative Example 1 are respectively. The first week charge gram capacity of PA-LNO in Example 1 is 300 mAh / g, and the discharge gram capacity is 210 mAh / g, which are significantly higher than 234 mAh / g (charge gram capacity) and 184 mAh / g (discharge gram capacity) of SS-LNO in Comparative Example 1. Figure 4 It can be seen from the dq / dv curve that the intensity of the redox reaction of PA-LNO is significantly higher than that of SS-LNO. This is because the porous material has a large contact area with the electrolyte and has more electrochemical reaction sites, thus being able to exert a higher capacity.

[0055] Figure 5 and Figure 6 The cycle performance test curves of the batteries made of the positive electrode materials in Example 1 and Example 5 and Comparative Example 1 are respectively ( Figure 5 0.2C; Figure 6 0.5C), it can be seen from the figure that at two rates, the PA-LNO material of Example 1 shows excellent cycling performance compared to the SS-LNO of Comparative Example 1. This is because the dense SS-LNO material cannot withstand the stress and strain caused by the insertion and removal of lithium ions during the cycle, and structural collapse and particle destruction will occur ( Figure 8 ), resulting in capacity decay. In comparison, the PA-LNO porous material of Example 1 can well absorb the stress and strain caused by the insertion and extraction of Li ions during the cycle, ensuring excellent cycle stability. The porous material in Example 5 further stabilizes the structure of the positive electrode material due to the doping of Co and Al, so under the test condition of the cycle test voltage of 0.05-5C, the capacity retention rate after 50 weeks of testing is greater than 94%, and the capacity retention rate after 100 weeks of testing is greater than 88%.

[0056] Figure 7 The test results (0.5C) of the cycle performance of the batteries made of the positive electrode materials in Examples 6 and 7 and Comparative Example 1 show that Al doping improves the cycle performance of the PA-LNO material in the examples.

[0057] Figure 8 The test results (0.5C) of the cycle performance of the batteries made of the positive electrode materials in Examples 8 and 9 and Comparative Example 1 show that the doping of Co improves the cycle performance of the PA-LNO material.

[0058] Fig. 9 The cycle performance test results (0.5C) of the batteries made of the positive electrode materials in Examples 10, 11, 12, Example 5 and Comparative Example 1 show that the doping of Mg improves the cycle performance of the materials. It can be seen that LiNi 0.8Co 0.13 Al 0.05 Mg 0.02 O 2 The porous material can still exert a gram capacity of 157mAh / g after 100 cycles of 0.5C / 0.5C charge and discharge, and the capacity retention rate is as high as 98%.

[0059] The button cell cycled for 50 cycles at 0.2C was disassembled under a protective atmosphere to obtain the positive electrode sheet after the cycle. After cleaning and drying, the positive electrode powder was scraped off and the particle morphology was observed under a transmission electron microscope. Fig.10 That is, the microscopic morphology of the positive electrode material particles of the battery made of the positive electrode material in Example 1 and Comparative Example 1 after 50 cycles at 0.2C is a transmission electron microscope image. The SS-LNO material particles (a, b) of Comparative Example 1 can be seen to have obvious voids and a large number of cracks, and some particles have even broken. In comparison, although a small number of voids appear in the PA-LNO material particles (c, d) of Example 1, no microcracks appear, and the material particles remain intact. The material synthesized after adding the polymer auxiliary has a porous structure, which can well buffer the expansion and contraction of the lattice and the stress and strain of the grains during the charge and discharge process, inhibit the appearance of microcracks and voids in the particles, prevent the particles from breaking, and ensure the integrity of the material during the cycle, thereby maintaining good cycle stability.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention rather than to limit them. Although the embodiments of the present invention have been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the embodiments of the present invention can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a positive electrode material for a lithium ion battery, Features: The positive electrode material is lithium oxide, and the positive electrode material is composed of spherical secondary particles composed of primary particles of lithium oxide, the average particle size of the primary particles is 100-200nm, and the secondary particles are distributed with a pore structure, and the pore diameter is 1-2μm; It includes the following steps: S01: Mix the metal salt and the lithium salt in a molar ratio of metal ion to lithium ion of 1:(1-1.3), add a volatile organic acid, wherein the amount of the volatile organic acid added is an amount capable of complexing all the metal salts in the raw materials with the metal ions in the lithium salt, and mix the three and grind them evenly; S02: mixing the ground product in S01 with an organic polymer in an amount of 1-3 mL per gram of ground product, and grinding them uniformly; the organic polymer comprises one or more of polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 2000, polyethylene glycol 6000, and polyethylene glycol 12000; S03: pre-sintering the ground product in S02 at 300-500°C for 4-10 hours; S04: Sinter the pre-sintered product in S03 at 750-950° C. for 6-15 hours, and obtain the desired lithium-ion battery positive electrode material after cooling.

2. The method for preparing the positive electrode material for a lithium ion battery according to claim 1, Features: In S01, the metal salt includes one or more combinations of oxalates, acetates, nitrates, and sulfates of Ni, Co, Mn, Al, Mg, Fe, Ti, Cr, Ga, Zn, V, Ge, and Sn elements.

3. The method for preparing the positive electrode material for a lithium ion battery according to claim 1, Features: In S01, the lithium salt includes one or a combination of multiple of lithium oxalate, lithium acetate, lithium nitrate, lithium sulfate, lithium hydroxide, and lithium carbonate.

4. The method for preparing the positive electrode material for a lithium ion battery according to claim 1, Features: In S01, the volatile organic acid includes a combination of one or more of oxalic acid, tartaric acid, malic acid, citric acid, benzoic acid, salicylic acid, caffeic acid, acetic acid, propionic acid, butyric acid, valeric acid, and isovaleric acid.

5. The method for preparing the positive electrode material for a lithium ion battery according to claim 1, Features: In S03, the pre-sintering temperature is 380-420°C; in S04, the sintering temperature is 800-850°C.

6. A lithium ion battery, wherein the positive electrode material is prepared by the preparation method as claimed in claim 1.

7. The lithium ion battery according to claim 6, Features: Under the test condition of a cycle test voltage of 0.05-5C, the capacity retention rate of the lithium-ion battery after 50 weeks of testing is greater than 94%, and the capacity retention rate after 100 weeks of testing is greater than 88%.

Images